The complement system

HylS', a fragment of truncated hyaluronidase of Streptococcus suis, contributes to immune evasion by interaction with host complement factor C3b

Pathogenic bacteria have evolved many strategies to evade surveillance and attack by complements. Streptococcus suis is an important zoonotic pathogen that infects humans and pigs. Hyaluronidase (HylA) has been reported to be a potential virulence factor of S. suis. However, in this study, it was discovered that the genomic region encoding HylA of the virulent S. suis strain SC19 and other ST1 strains was truncated into four fragments when aligned with a strain containing intact HylA and possessing hyaluronidase activity. As a result, SC19 had no hyaluronidase activity, but one truncated HylA fragment, designated as HylS,' directly interacted with complement C3b, as confirmed by western ligand blotting, pull-down, and ELISA assays. The deposition of C3b and membrane attack complex (MAC) formation on the surface of a HylS'-deleted mutant (ΔhylS') was significantly increased compared to wild-type SC19. In human sera and whole blood, ΔhylS' survival was significantly reduced compared to that in SC19. The resistance of ΔhylS' to macrophages and human polymorphonuclear neutrophil PMNs also decreased. In a mouse infection model, ΔhylS' showed reduced lethality and lower bacterial load in the organs compared to that of SC19. We conclude that the truncated hyaluronidase HylS' fragment contributes to complement evasion and the pathogenesis of S. suis.

The role and treatment potential of the complement pathway in chronic pain

The role of the complement system in pain syndromes has garnered attention on the back of preclinical and clinical evidence supporting its potential as a target for new analgesic pharmacotherapies. Of the components that make up the complement system, component 5a (C5a) and component 3a (C3a) are most strongly and consistently associated with pain. Receptors for C5a are widely found in immune resident cells (microglia, astrocytes, sensory neuron-associated macrophages (sNAMs)) in the central nervous system (CNS) as well as hematogenous immune cells (mast cells, macrophages, T-lymphocytes, etc.). When active, as is often observed in chronic pain conditions, these cells produce various inflammatory mediators including pro-inflammatory cytokines. These events can trigger nervous tissue inflammation (neuroinflammation) which coexists with and potentially maintains peripheral and central sensitization. C5a has a likely critical role in initiating this process highlighting its potential as a promising non-opioid target for treating pain. This review summarises the most up-to-date research on the role of the complement system in pain with emphasis on the C5 pathway in peripheral tissue, dorsal root ganglia (DRG) and the CNS, and explores advances in complement-targeted drug development and sex differences. A perspective on the optimal application of different C5a inhibitors for different types (e.g., neuropathic, post-surgical and chemotherapy-induced pain, osteoarthritis pain) and stages (e.g., acute, subacute, chronic) of pain is also provided to help guide future clinical trials. PERSPECTIVE: This review highlights the role and mechanisms of complement components and their receptors in physiological and pathological pain. The potential of complement-targeted therapeutics for the treatment of chronic pain is also explored with a focus on C5a inhibitors to help guide future clinical trials.

Impact of the Graphene Production Methods Sonication and Microfluidization on In Vitro and In Vivo Toxicity, Macrophage Response, and Complement Activation

Graphene, a material composed of a two-dimensional lattice of carbon atoms, has due to its many unique properties a wide array of potential applications in the biomedical field. One of the most common production methods is exfoliation through sonication, which is simple but has low yields. Another approach, using microfluidization, has shown promise through its scalability for commercial production. Regardless of their production method, materials made for biomedical applications need to be tested for biocompatibility. Here, we investigated the differences in toxicity, macrophage response, and complement activation of similar-sized graphene flakes produced through sonication and microfluidization, using in vitro cell assays and in vivo assays on zebrafish larvae. In vitro toxicity testing showed that sonicated graphene had a high toxicity, with an EC50 of 100 μg mL-1 for endothelial cells and 60 μg mL-1 for carcinoma cells. In contrast, microfluidized graphene did not reach EC50 at any of the tested concentrations. The potency to activate the complement system in whole blood was 10-fold higher for sonicated than for microfluidized graphene. In zebrafish larvae, graphene of either production method was found to mainly agglomerate in the caudal hematopoietic tissue; however, no acute toxic effects were found. Sonicated graphene led to an increase in macrophage count and a macrophage migration to the ventral tail area, while microfluidized graphene led to a transient reduction in macrophage count and fewer cells in the ventral trail area. The observed reduction in macrophages and change in macrophage distribution following exposure to microfluidized graphene was less pronounced compared to sonicated graphene and contributed to masking of the fluorescent signal rather than cytotoxic effects. Summarized, we observed higher toxicity, macrophage response, and complement activation with graphene produced through sonication, which could be due to oxygen-containing functional groups introduced to the edge of the carbon lattice by this production method. These findings indicate that microfluidization produces graphene more suitable for biomedical applications.

Host heterogeneity in humoral bactericidal activity can be complement independent

Background

Humoral bactericidal activity was first recognized nearly a century ago. However, the extent of inter-individual heterogeneity and the mechanisms underlying such heterogeneity beyond antibody or complement systems have not been well studied.

Methods

The plasma bactericidal activity of five healthy volunteers were tested against 30 strains of Gram-negative uropathogens, Klebsiella pneumoniae and Escherichia coli, associated with bloodstream infections. IgG and IgM titers specific to K. pneumoniae strains KP13883 and KPB1 were measured by ELISA, and complement inhibitor was used to measure the contribution of complement-induced killing. Furthermore, MALDI-TOF mass spectrometry was conducted to determine the metabolomic components of plasma with bactericidal properties in 25 healthy individuals using Bayesian inference of Pearson correlation between peak intensity and colony counts of surviving bacteria.

Results

Plasma bactericidal activity varied widely between individuals against various bacterial strains. While individual plasma with higher IgM titers specific to K. pneumoniae strain KP13883 showed more efficient killing of the strain, both IgM and IgG titers for K. pneumoniae strain KPB1 did not correlate well with the killing activity. Complement inhibition assays elucidated that the complement-mediated killing was not responsible for the inter-individual heterogeneity in either isolate. Subsequently, using MALDI-TOF mass spectrometry on plasmas of 25 healthy individuals, we identified several small molecules including gangliosides, pediocins, or saponins as candidates that showed negative correlation between peak intensities and colony forming units of the test bacteria.

Conclusion

This is the first study to demonstrate the inter-individual heterogeneity of constitutive innate humoral bactericidal function quantitatively and that the heterogeneity can be independent of antibody or the complement system.

Management dilemma: managing bipolar affective disorder in a patient with hereditary angioedema

Hereditary angioedema (HAE) is a rare autosomal dominant disorder caused by the deficiency or dysfunction of C1 esterase inhibitors. We present a case of a female in her 50s with HAE and bipolar affective disorder (BPAD). She has experienced severe depressive and manic episodes with significant disruption to her life. She has also had potentially life-threatening episodes of recurrent angioedema with severe facial and body swelling and post-pharyngeal symptoms.She presented to us with a depressive episode with suicidal ideation. Her angioedema was flared by both psychological stressors and psychotropic medications. Choosing the correct mood stabiliser without triggering angioedema was a major challenge in her treatment. Also, psychosocial interventions and frequent liaison with her immunology team were necessary to provide her with optimum care in the community. Here, we discuss the challenges we faced and how we overcame them in managing this rare presentation of coexisting BPAD and HAE.

Controlling Candida: immune regulation of commensal fungi in the gut

The intestinal microbiome harbors fungi that pose a significant risk to human health as opportunistic pathogens and drivers of inflammation. Inflammatory and autoimmune diseases are associated with dysbiotic fungal communities and the expansion of potentially pathogenic fungi. The gut is also the main reservoir for disseminated fungal infections. Immune interactions are critical for preventing commensal fungi from becoming pathogenic. Significant strides have been made in defining innate and adaptive immune pathways that regulate intestinal fungi, and these discoveries have coincided with advancements in our understanding of the fungal molecular pathways and effectors involved in both commensal colonization and pathogenesis within the gut. In this review, we will discuss immune interactions important for regulating commensal fungi, with a focus on how specific cell types and effectors interact with fungi to limit their colonization or pathogenic potential. This will include how innate and adaptive immune pathways target fungi and orchestrate antifungal immune responses, in addition to how secreted immune effectors, such as mucus and antimicrobial peptides, regulate fungal colonization and inhibit pathogenic potential. These immune interactions will be framed around our current understanding of the fungal effectors and pathways regulating colonization and pathogenesis within this niche. Finally, we highlight important unexplored mechanisms by which the immune system regulates commensal fungi in the gut.

Elevated C1s/C1-INH in serum and plasma of myasthenia gravis patients

Myasthenia Gravis (MG) is an autoimmune neuromuscular disorder where acetylcholine receptor (AChR) antibodies induce membrane attack complex formation at the muscle membrane. The C1-inhibitor (C1-INH) regulates the classical pathway and is a promising marker in other autoimmune disorders. Treatment options for AChR antibody MG include complement inhibitors; nevertheless, the early pathway activation in MG remains unclear. Serum and plasma C1s-C1-INH levels were higher in MG patients than in matched healthy controls, supporting early classical pathway activation in most MG patients. These findings allow prospective validation studies of activated C1s as a putative treatment target and potential accompanying biomarker in MG.

Ketamine's mechanism of action with an emphasis on neuroimmune regulation: can the complement system complement ketamine's antidepressant effects?

Over 300 million people worldwide suffer from major depressive disorder (MDD). Unfortunately, only 30-40% of patients with MDD achieve complete remission after conventional monoamine antidepressant therapy. In recent years, ketamine has revolutionized the treatment of MDD, with its rapid antidepressant effects manifesting within a few hours as opposed to weeks with conventional antidepressants. Many research endeavors have sought to identify ketamine's mechanism of action in mood disorders; while many studies have focused on ketamine's role in glutamatergic modulation, several studies have implicated its role in regulating neuroinflammation. The complement system is an important component of the innate immune response vital for synaptic plasticity. The complement system has been implicated in the pathophysiology of depression, and studies have shown increases in complement component 3 (C3) expression in the prefrontal cortex of suicidal individuals with depression. Given the role of the complement system in depression, ketamine and the complement system's abilities to modulate glutamatergic transmission, and our current understanding of ketamine's anti-inflammatory properties, there is reason to suspect a common link between the complement system and ketamine's mechanism of action. This review will summarize ketamine's anti- inflammatory roles in the periphery and central nervous system, with an emphasis on complement system regulation.

The Promise of Complement Therapeutics in Solid Organ Transplantation

Transplantation is the ideal therapy for end-stage organ failure, but outcomes for all transplant organs are suboptimal, underscoring the need to develop novel approaches to improve graft survival and function. The complement system, traditionally considered a component of innate immunity, is now known to broadly control inflammation and crucially contribute to induction and function of adaptive T-cell and B-cell immune responses, including those induced by alloantigens. Interest of pharmaceutical industries in complement therapeutics for nontransplant indications and the understanding that the complement system contributes to solid organ transplantation injury through multiple mechanisms raise the possibility that targeting specific complement components could improve transplant outcomes and patient health. Here, we provide an overview of complement biology and review the roles and mechanisms through which the complement system is pathogenically linked to solid organ transplant injury. We then discuss how this knowledge has been translated into novel therapeutic strategies to improve organ transplant outcomes and identify areas for future investigation. Although the clinical application of complement-targeted therapies in transplantation remains in its infancy, the increasing availability of new agents in this arena provides a rich environment for potentially transformative translational transplant research.

In silico analysis and functional characterization of a leucine-rich repeat protein of Leptospira interrogans

Pathogenic spirochetes of the genus Leptospira are the causative agent of leptospirosis, a widely disseminated zoonosis that affects humans and animals. The ability of leptospires to quickly cross host barriers causing infection is not yet fully understood. Thus, understanding the mechanisms of pathogenicity is important to combat leptospiral infection. Outer membrane proteins are interesting targets to study as they are able to interact with host molecules. Proteins containing leucine-rich repeat (LRR) domains are characterized by the presence of multiple regions containing leucine residues and they have putative functions related to host-pathogen interactions. Hence, the present study aimed to clone and express the recombinant protein encoded by the LIC11098 gene, an LRR protein of L. interrogans serovar Copenhageni. In silico analyses predicted that the target protein is conserved among pathogenic strains of Leptospira, having a signal peptide and multiple LRR domains. The DNA sequence encoding the LRR protein was cloned in frame into the pAE vector, expressed without mutations in Escherichia coli and purified by His-tag chromatography. Circular dichroism (CD) spectrum showed that the recombinant protein was predominantly composed of β-sheets. A dose-dependent interaction was observed with cellular and plasma fibronectins, laminin and the complement system component C9, suggesting a possible role of the protein encoded by LIC11098 gene at the initial stages of infection.

Pharmacokinetics, pharmacodynamics, safety, and tolerability of a single-dose riliprubart, an anti-C1s humanized monoclonal antibody in East-Asian adults: results from a Phase 1, randomized, open-label trial

OBJECTIVES

This Phase 1 trial was planned to investigate the pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability of a single dose of riliprubart in healthy East-Asian adult participants.

METHODS

A single-center, parallel-group, randomized, open-label, single-dose study was performed to evaluate the PK, PD, safety, and tolerability of riliprubart (50 mg/kg intravenous [IV] or 600 mg subcutaneous [SC]) in 37 healthy East-Asian (Chinese, Japanese, and Korean) participants.

RESULTS

Riliprubart was slowly absorbed after SC administration (median tmax: 7.01-10.48 days) and showed a long half-life after IV or SC administration (mean: 9.52-11.0 weeks), with a bioavailability of 74.6% after SC administration. The PD profiles, which are evaluated by classical complement pathway activity or CH50, were similar and largely overlapped across East-Asian participants after a single IV or SC dose. Riliprubart was safe and well tolerated in participants following a single IV or SC dose.

CONCLUSIONS

Riliprubart was safe and well tolerated and demonstrated favorable PK and PD profiles in healthy East-Asian participants following a single IV or SC dose. These results are comparable to first-in-human study results from non-East-Asian participants and support the same dosing regimen of riliprubart for global simultaneous clinical development.

CLINICAL TRIAL REGISTRATION

This trial is registered at https://cris.nih.go.kr (identifier: KCT0006571).

Delayed Cerebral Ischemia After Aneurysmal Subarachnoid Hemorrhage: The Role of the Complement and Innate Immune System

Specific inflammatory pathways are important in the development of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage. Understanding the specific pathways of inflammation may be critical for finding new treatments. Evidence is accumulating that innate inflammatory cells and proteins play a more important role than cells of the adaptive inflammatory system. In this work, we review the evidence from clinical and preclinical data regarding which cells of the immune system play a role in DCI with particular emphasis on the bone-marrow-derived cells monocytes and neutrophils and the brain parenchymal microglia. In addition, we will review the evidence that complement proteins, a non-cellular part of the innate immune system, play a role in the development of DCI.

Advancements in Imaging and Therapeutic Options for Dry Age-Related Macular Degeneration and Geographic Atrophy

Age-related macular degeneration (AMD) is a leading cause of vision loss in the elderly, with dry AMD (d-AMD) leading to geographic atrophy (GA) and significant visual impairment. Multimodal imaging plays a crucial role in d-AMD diagnosis and management, allowing for detailed classification of patient phenotypes and aiding in treatment planning and prognosis determination. Treatment approaches for d-AMD have recently witnessed profound change with the development of specific drugs targeting the complement cascade, with the first anticomplement agents recently approved for GA treatment. Additionally, emerging strategies such as gene therapy and laser treatments may offer potential benefits, though further research is needed to fully establish their efficacy. However, the lack of effective therapies capable of restoring damaged retinal cells remains a major challenge. In the future, genetic treatments aimed at preventing the progression of d-AMD may emerge as a powerful approach. Currently, however, their development is still in the early stages.

Effects of drug-induced liver injury on the in vivo fate of liposomes

Liposomes represent one of the most extensively studied nano-carriers due to their potential in targeted drug delivery. However, the complex in vivo fate, particularly under pathological conditions, presents challenges for clinical translation of liposomal therapeutics. Liver serves as the most important organ for liposome accumulation and metabolism. Unfortunately, the fate of liposomes under pathological liver conditions has been significantly overlooked. This study aimed to investigate the in vivo pharmacokinetic profile and biodistribution profile of liposomes under drug-induced liver injury (DILI) conditions. Two classic DILI animal models, i.e. acetaminophen-induced acute liver injury (AILI) and triptolide-induced subacute liver injury (TILI), were established to observe the effect of pathological liver conditions on the in vivo performance of liposomes. The study revealed significant changes in the in vivo fate of liposomes following DILI, including prolonged blood circulation and enhanced hepatic accumulation of liposomes. Changes in the composition of plasma proteins and mononuclear phagocyte system (MPS)-related cell subpopulations collectively led to the altered in vivo fate of liposomes under liver injury conditions. Despite liver injury, macrophages remained the primary cells responsible for liposomes uptake in liver, with the recruited monocyte-derived macrophages exhibiting enhanced ability to phagocytose liposomes under pathological conditions. These findings indicated that high capture of liposomes by the recruited hepatic macrophages not only offered potential solutions for targeted delivery, but also warned the clinical application of patients under pathological liver conditions.

The role of MASP1 in the complement system and expression characteristics in response to GCRV infection in grass carp

The grass carp (Ctenopharyngodon idella) constitutes a significant economic resource within the aquaculture sector of our nation, yet it has been chronically afflicted by the Grass Carp Reovirus (GCRV) disease. The complement system, a vital component of fish's innate immunity, plays a crucial role in combating viral infections. This research investigates the potential role of MASP1, a key molecule in the lectin pathway of the complement system, in the GCRV infection in grass carp. An analysis of the molecular characteristics of MASP1 in grass carp revealed that its identity and similarity percentages range from 35.10 to 91.00 % and 35.30-91.00 %, respectively, in comparison to other species. Phylogenetically, MASP1 in C. idella aligns closely with species such as Danio rerio, Cyprinus carpio, and Carassius carassius, exhibiting chromosomal collinearity with the zebrafish. Subsequent tissue analysis in both healthy and GCRV-infected grass carp indicated that MASP1's basal expression was predominantly in the liver. Post-GCRV infection, MASP1 expression in various tissues exhibited temporal variations: peaking in the liver on day 5, spleen on day 7, and kidney on day 14. Furthermore, employing Complement Component 3 (C3) as a benchmark for complement system activation, it was observed that MASP1 could activate and cleave C3 to C3b. MASP1 also demonstrated an inhibitory effect on GCRV replication (compared with the control group, VP2 and VP7 decreased by 6.82-fold and 4.37-fold) and enhanced the expression of antiviral genes, namely IRF3, IRF7 and IFN1 (compared with the control group, increased 2.25-fold, 45.38-fold and 22.37-fold, respectively). In vivo protein injection experiments substantiated MASP1's influence on the relative mRNA expression levels of C3 in various tissues and its protein expression in serum. This study also verified that C3 could modulate the expression of antiviral genes such as IFN1 and IRF3.

Potential role of CTSS in AMDImmune modulatory and anti-angiogenic effects of cathepsin S knockdown in ARPE-19 cells

We aimed to determine the role of cathepsin S (CTSS) in modulating oxidative stress-induced immune and inflammatory reactions and angiogenesis in age-related macular degeneration. Human retinal pigment epithelium cells line ARPE-19 (immature) were maintained and treated with H2O2. The expression of CTSS, inflammatory cytokines, and complement factors induced by oxidative stress was compared between cells incubated without (control) and with CTSS knockdown (using small interfering ribonucleic acid; siRNA). To evaluate the role of CTSS in angiogenesis, we assayed tube formation using human umbilical vein endothelial cells and conditioned medium from ARPE-19 cells. We also used a mouse model of laser-induced choroidal neovascularization. CTSS levels were higher in ARPE-19 cells treated with H2O2 than in control cells. Oxidative stress-induced CTSS resulted in significantly elevated transcription of nuclear factor kappa B-dependent inflammatory cytokines, complement factors C3a and C5a, membrane attack complex (C5b-9), and C3a and C5a receptors. siRNA-mediated knockdown of CTSS reduced the number of inflammatory signals. Furthermore, oxidative stress-induced CTSS regulated the expression of peroxisome proliferator-activated receptor γ and vascular endothelial growth factor A/Akt serine/threonine kinase family signaling, which led to angiogenesis. Tube formation assays and mouse models of choroidal neovascularization revealed that CTSS knockdown ameliorated angiogenesis in vitro and in vivo. The present findings suggest that CTSS modulates the complement pathway, inflammatory reactions, and neovascularization, and that CTSS knockdown induces potent immunomodulatory effects. Hence, it could be a promising target for the prevention and treatment of early- and late-stage age-related macular degeneration.

Serum susceptibility of Escherichia coli and its association with patient clinical outcomes

The innate immune system eliminates bloodstream pathogens such as Escherichia coli in part through complement protein deposition and subsequent bacterial death (i.e., "serum killing"). Some E. coli strains have developed mechanisms to resist serum killing, though the extent of variation in serum killing among bloodstream infection (BSI) isolates and the clinical impact of this variation is not well understood. To address this issue, we developed a novel assay that uses flow cytometry to perform high throughput serum bactericidal assays (SBAs) with E. coli BSI isolates (n = 183) to define the proportion of surviving bacteria after exposure to serum. We further determined whether E. coli resistance to serum killing is associated with clinical outcomes (e.g., in-hospital attributable mortality, in-hospital total mortality, septic shock) and bacterial genotype in the corresponding patients with E. coli BSI. Our novel flow cytometry-based SBA performed similarly to a traditional SBA, though with significantly decreased hands-on bench work. Among E. coli BSI isolates, the mean proportion that survived exposure to 25% serum was 0.68 (Standard deviation 0.02, range 0.57-0.93). We did not identify associations between E. coli resistance to serum killing and clinical outcomes in our adjusted models. Together, this study describes a novel flow cytometry-based approach to the bacterial SBA that allowed for high-throughput testing of E. coli BSI isolates and identified high variability in resistance to serum killing among a large set of BSI isolates.

Preliminary study of BF/C2 on immune mechanism of grass carp against GCRV infection

BF/C2 is a crucial molecule in the coagulation complement cascade pathway and plays a significant role in the immune response of grass carp through the classical, alternative, and lectin pathways during GCRV infection. In vivo experiments demonstrated that the mRNA expression levels of BF/C2 (A, B) in grass carp positively correlated with GCRV viral replication at various stages of infection. Excessive inflammation leading to death coincided with peak levels of BF/C2 (A, B) mRNA expression and GCRV viral replication. Correspondingly, BF/C2 (A, B) recombinant protein, CIK cells and GCRV co-incubation experiments yielded similar findings. Therefore, 3 h (incubation period) and 9 h (death period) were selected as critical points for this study. Transcriptome sequencing analysis revealed significant differences in the expression of BF/C2A and BF/C2B during different stages of CIK infection with GCRV and compared to the blank control group (PBS). Specifically, the BF/C2A_3 and BF/C2A_9 groups exhibited 2729 and 2228 differentially expressed genes (DEGs), respectively, with 1436 upregulated and 1293 downregulated in the former, and 1324 upregulated and 904 downregulated in the latter. The BF/C2B_3 and BF/C2B_9 groups showed 2303 and 1547 DEGs, respectively, with 1368 upregulated and 935 downregulated in the former, and 818 upregulated and 729 downregulated in the latter. KEGG functional enrichment analysis of these DEGs identified shared pathways between BF/C2A and PBS groups at 3 and 9 h, including the C-type lectin receptor signaling pathway, protein processing in the endoplasmic reticulum, Toll-like receptor signaling pathway, Salmonella infection, apoptosis, tight junction, and adipocytokine signaling pathway. Additionally, the BF/C2B groups at 3 and 9 h shared pathways related to protein processing in the endoplasmic reticulum, glycolysis/gluconeogenesis, and biosynthesis of amino acids. The mRNA levels of these DEGs were validated in cellular models, confirming consistency with the sequencing results. In addition, the mRNA expression levels of these candidate genes (mapk1, il1b, rela, nfkbiab, akt3a, hyou1, hsp90b1, dnajc3a et al.) in the head kidney, kidney, liver and spleen of grass carp immune tissue were significantly different from those of the control group by BF/C2 (A, B) protein injection in vivo. These candidate genes play an important role in the response of BF/C2 (A, B) to GCRV infection and it also further confirmed that BF/C2 (A, B) of grass carp plays an important role in coping with GCRV infection.

A multiomic atlas of the aging hippocampus reveals molecular changes in response to environmental enrichment

Aging involves the deterioration of organismal function, leading to the emergence of multiple pathologies. Environmental stimuli, including lifestyle, can influence the trajectory of this process and may be used as tools in the pursuit of healthy aging. To evaluate the role of epigenetic mechanisms in this context, we have generated bulk tissue and single cell multi-omic maps of the male mouse dorsal hippocampus in young and old animals exposed to environmental stimulation in the form of enriched environments. We present a molecular atlas of the aging process, highlighting two distinct axes, related to inflammation and to the dysregulation of mRNA metabolism, at the functional RNA and protein level. Additionally, we report the alteration of heterochromatin domains, including the loss of bivalent chromatin and the uncovering of a heterochromatin-switch phenomenon whereby constitutive heterochromatin loss is partially mitigated through gains in facultative heterochromatin. Notably, we observed the multi-omic reversal of a great number of aging-associated alterations in the context of environmental enrichment, which was particularly linked to glial and oligodendrocyte pathways. In conclusion, our work describes the epigenomic landscape of environmental stimulation in the context of aging and reveals how lifestyle intervention can lead to the multi-layered reversal of aging-associated decline.

Recruitment of Vitronectin by Bacterial Pathogens: A Comprehensive Overview

The key factor that enables pathogenic bacteria to establish successful infections lies largely in their ability to escape the host's immune response and adhere to host surfaces. Vitronectin (Vn) is a multidomain glycoprotein ubiquitously present in blood and the extracellular matrix of several tissues, where it plays important roles as a regulator of membrane attack complex (MAC) formation and as a mediator of cell adhesion. Vn has emerged as an intriguing target for several microorganisms. Vn binding by bacterial receptors confers protection from lysis resulting from MAC deposition. Furthermore, through its Arg-Gly-Asp (RGD) motif, Vn can bind several host cell integrins. Therefore, Vn recruited to the bacterial cell functions as a molecular bridge between bacteria and host surfaces, where it triggers several host signaling events that could promote bacterial internalization. Each bacterium uses different receptors that recognize specific Vn domains. In this review, we update the current knowledge of Vn receptors of major bacterial pathogens, emphasizing the role they may play in the host upon Vn binding. Focusing on the structural properties of bacterial proteins, we provide details on the residues involved in their interaction with Vn. Furthermore, we discuss the possible involvement of Vn adsorption on biomaterials in promoting bacterial adhesion on abiotic surfaces and infection.

Plasma complement and coagulation proteins as prognostic factors of negative symptoms: An analysis of the NAPLS 2 and 3 studies

INTRODUCTION

Negative symptoms impact the quality of life of individuals with psychosis and current treatment options for negative symptoms have limited effectiveness. Previous studies have demonstrated that complement and coagulation pathway protein levels are related to later psychotic experiences, psychotic disorder, and functioning. However, the prognostic relationship between complement and coagulation proteins and negative symptoms is poorly characterised.

METHODS

In the North American Prodrome Longitudinal Studies 2 and 3, negative symptoms in 431 individuals at clinical high-risk for psychosis (mean age: 18.2, SD 3.6; 42.5 % female) were measured at multiple visits over 2 years using the Scale of Psychosis-Risk Symptoms. Plasma proteins were quantified at baseline using mass spectrometry. Four factors were derived to represent levels of proteins involved in the activation or regulation of the complement or coagulation systems. The relationships between standardised protein group factors and serial measurements of negative symptoms over time were modelled using generalised least squares regression. Analyses were adjusted for baseline candidate prognostic factors: negative symptoms, positive symptoms, functioning, depressive symptoms, suicidal ideation, cannabis use, tobacco use, antipsychotic use, antidepressant use, age, and sex.

RESULTS

Clinical and demographic prognostic factors of follow-up negative symptoms included negative, positive, and depressive symptoms, functioning, and age. Adjusting for all candidate prognostic factors, the complement regulators group and the coagulation regulators group were identified as prognostic factors of follow-up negative symptoms (β: 0.501, 95 % CI: 0.160, 0.842; β: 0.430, 95 % CI: 0.080, 0.780 respectively. The relationship between complement regulator levels and negative symptoms was also observed in NAPLS2 alone (β: 0.501, 95 % CI: -0.037, 1.039) and NAPLS3 alone, additionally adjusting for BMI (β: 0.442, 95 % CI: 0.127, 0.757).

CONCLUSION

The results indicate that plasma complement and coagulation regulator levels are prognostic factors of negative symptoms, independent of clinical and demographic prognostic factors. These results suggest complement and coagulation regulator levels could have potential utility in informing treatment decisions for negative symptoms in individuals at risk.

Association of Complement Factors With Disability Progression in Primary Progressive Multiple Sclerosis

BACKGROUND AND OBJECTIVES

The complement system is known to play a role in multiple sclerosis (MS) pathogenesis. However, its contribution to disease progression remains elusive. The study investigated the role of the complement system in disability progression of patients with primary progressive MS (PPMS).

METHODS

Sixty-eight patients with PPMS from 12 European MS centers were included in the study. Serum and CSF levels of a panel of complement components (CCs) were measured by multiplex enzyme-linked immunosorbent assay at a baseline time point (i.e., sampling). Mean (SD) follow-up time from baseline was 9.6 (4.8) years. Only one patient (1.5%) was treated during follow-up. Univariable and multivariable logistic regressions adjusted for age, sex, and albumin quotient were performed to assess the association between baseline CC levels and disability progression in short term (2 years), medium term (6 years), and long term (at the time of the last follow-up).

RESULTS

In short term, CC played little or no role in disability progression. In medium term, an elevated serum C3a/C3 ratio was associated with a higher risk of disability progression (adjusted OR 2.30; 95% CI 1.17-6.03; p = 0.040). By contrast, increased CSF C1q levels were associated with a trend toward reduced risk of disability progression (adjusted OR 0.43; 95% CI 0.17-0.98; p = 0.054). Similarly, in long term, an elevated serum C3a/C3 ratio was associated with higher risk of disability progression (adjusted OR 1.81; 95% CI 1.09-3.40; p = 0.037), and increased CSF C1q levels predicted lower disability progression (adjusted OR 0.41; 95% CI 0.17-0.86; p = 0.025).

DISCUSSION

Proteins involved in the activation of early complement cascades play a role in disability progression as risk (elevated serum C3a/C3 ratio) or protective (elevated CSF C1q) factors after 6 or more years of follow-up in patients with PPMS. The protective effects associated with C1q levels in CSF may be related to its neuroprotective and anti-inflammatory properties.

Common virulence factors between Histoplasma and Paracoccidioides: Recognition of Hsp60 and Enolase by CR3 and plasmin receptors in host cells

Over the last two decades, the incidence of Invasive Fungal Infections (IFIs) globally has risen, posing a considerable challenge despite available antifungal therapies. Addressing this, the World Health Organization (WHO) prioritized research on specific fungi, notably Histoplasma spp. and Paracoccidioides spp. These dimorphic fungi have a mycelial life cycle in soil and a yeast phase associated with tissues of mammalian hosts. Inhalation of conidia and mycelial fragments initiates the infection, crucially transforming into the yeast form within the host, influenced by factors like temperature, host immunity, and hormonal status. Survival and multiplication within alveolar macrophages are crucial for disease progression, where innate immune responses play a pivotal role in overcoming physical barriers. The transition to pathogenic yeast, triggered by increased temperature, involves yeast phase-specific gene expression, closely linked to infection establishment and pathogenicity. Cell adhesion mechanisms during host-pathogen interactions are intricately linked to fungal virulence, which is critical for tissue colonization and disease development. Yeast replication within macrophages leads to their rupture, aiding pathogen dissemination. Immune cells, especially macrophages, dendritic cells, and neutrophils, are key players during infection control, with macrophages crucial for defense, tissue integrity, and pathogen elimination. Recognition of common virulence molecules such as heat- shock protein-60 (Hsp60) and enolase by pattern recognition receptors (PRRs), mainly via the complement receptor 3 (CR3) and plasmin receptor pathways, respectively, could be pivotal in host-pathogen interactions for Histoplasma spp. and Paracoccidioides spp., influencing adhesion, phagocytosis, and inflammatory regulation. This review provides a comprehensive overview of the dynamic of these two IFIs between host and pathogen. Further research into these fungi's virulence factors promises insights into pathogenic mechanisms, potentially guiding the development of effective treatment strategies.

Effect of an endothelial regulatory module on plasma proteomics in exercising horses

Elite performing exercise requires an intricate modulation of the blood pressure to support the working muscles with oxygen. We have previously identified a genomic regulatory module that associates with differences in blood pressures of importance for elite performance in racehorses. This study aimed to determine the effect of the regulatory module on the protein repertoire. We sampled plasma from 12 Coldblooded trotters divided into two endothelial regulatory module haplotype groups, a sub-elite performing haplotype (SPH) and an elite performing haplotype (EPH), each at rest and exercise. The haplotype groups and their interaction were interrogated in two analyses, i) individual paired ratio analysis for identifying differentially abundant proteins of exercise (DAPE) and interaction (DAPI) between haplotype and exercise, and ii) unpaired ratio analysis for identifying differentially abundant protein of haplotype (DAPH). The proteomics analyses revealed a widespread change in plasma protein content during exercise, with a decreased tendency in protein abundance that is mainly related to lung function, tissue fluids, metabolism, calcium ion pathway and cellular energy metabolism. Furthermore, we provide the first investigation of the proteome variation due to the interaction between exercise and related blood pressure haplotypes, which this difference was related to a faster switch to the lipoprotein and lipid metabolism during exercise for EPH. The molecular signatures identified in the present study contribute to an improved understanding of exercise-related blood pressure regulation.

Is the Complement System Dysregulated in Preeclampsia Comorbid with HIV Infection?

South Africa is the epicentre of the global HIV pandemic, with 13.9% of its population infected. Preeclampsia (PE), a hypertensive disorder of pregnancy, is often comorbid with HIV infection, leading to multi-organ dysfunction and convulsions. The exact pathophysiology of preeclampsia is triggered by an altered maternal immune response or defective development of maternal tolerance to the semi-allogenic foetus via the complement system. The complement system plays a vital role in the innate immune system, generating inflammation, mediating the clearance of microbes and injured tissue materials, and a mediator of adaptive immunity. Moreover, the complement system has a dual effect, of protecting the host against HIV infection and enhancing HIV infectivity. An upregulation of regulatory proteins has been implicated as an adaptive phenomenon in response to elevated complement-mediated cell lysis in HIV infection, further aggravated by preeclamptic complement activation. In light of the high prevalence of HIV infection and preeclampsia in South Africa, this review discusses the association of complement proteins and their role in the synergy of HIV infection and preeclampsia in South Africa. It aims to identify women at elevated risk, leading to early diagnosis and better management with targeted drug therapy, thereby improving the understanding of immunological dysregulation.

Challenges and Pitfalls of Research Designs Involving Magnesium-Based Biomaterials: An Overview

Magnesium-based biomaterials hold remarkable promise for various clinical applications, offering advantages such as reduced stress-shielding and enhanced bone strengthening and vascular remodeling compared to traditional materials. However, ensuring the quality of preclinical research is crucial for the development of these implants. To achieve implant success, an understanding of the cellular responses post-implantation, proper model selection, and good study design are crucial. There are several challenges to reaching a safe and effective translation of laboratory findings into clinical practice. The utilization of Mg-based biomedical devices eliminates the need for biomaterial removal surgery post-healing and mitigates adverse effects associated with permanent biomaterial implantation. However, the high corrosion rate of Mg-based implants poses challenges such as unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. The biocompatibility and degradability of materials based on magnesium have been studied by many researchers in vitro; however, evaluations addressing the impact of the material in vivo still need to be improved. Several animal models, including rats, rabbits, dogs, and pigs, have been explored to assess the potential of magnesium-based materials. Moreover, strategies such as alloying and coating have been identified to enhance the degradation rate of magnesium-based materials in vivo to transform these challenges into opportunities. This review aims to explore the utilization of Mg implants across various biomedical applications within cellular (in vitro) and animal (in vivo) models.

Urinary complement biomarkers in immune-mediated kidney diseases

The complement system, an important part of the innate system, is known to play a central role in many immune mediated kidney diseases. All parts of the complement system including the classical, alternative, and mannose-binding lectin pathways have been implicated in complement-mediated kidney injury. Although complement components are thought to be mainly synthesized in the liver and activated in the circulation, emerging data suggest that complement is synthesized and activated inside the kidney leading to direct injury. Urinary complement biomarkers are likely a better reflection of inflammation within the kidneys as compared to traditional serum complement biomarkers which may be influenced by systemic inflammation. In addition, urinary complement biomarkers have the advantage of being non-invasive and easily accessible. With the rise of therapies targeting the complement pathways, there is a critical need to better understand the role of complement in kidney diseases and to develop reliable and non-invasive biomarkers to assess disease activity, predict treatment response and guide therapeutic interventions. In this review, we summarized the current knowledge on urinary complement biomarkers of kidney diseases due to immune complex deposition (lupus nephritis, primary membranous nephropathy, IgA nephropathy) and due to activation of the alternative pathway (C3 glomerulopathy, thrombotic microangiography, ANCA-associated vasculitis). We also address the limitations of current research and propose future directions for the discovery of urinary complement biomarkers.

Immunopathogenesis of multiple sclerosis: molecular and cellular mechanisms and new immunotherapeutic approaches

BACKGROUND

Multiple sclerosis (MS) is a central nervous system (CNS) demyelinating autoimmune disease with increasing global prevalence. It predominantly affects females, especially those of European descent. The interplay between environmental factors and genetic predisposition plays a crucial role in MS etiopathogenesis.

METHODS

We searched recent relevant literature on reputable databases, which include, PubMed, Embase, Web of Science, Scopus, and ScienceDirect using the following keywords: multiple sclerosis, pathogenesis, autoimmunity, demyelination, therapy, and immunotherapy.

RESULTS

Various animal models have been employed to investigate the MS etiopathogenesis and therapeutics. Autoreactive T cells within the CNS recruit myeloid cells through chemokine expression, leading to the secretion of inflammatory cytokines driving the MS pathogenesis, resulting in demyelination, gliosis, and axonal loss. Key players include T cell lymphocytes (CD4+ and CD8+), B cells, and neutrophils. Signaling dysregulation in inflammatory pathways and the immunogenetic basis of MS are essential considerations for any successful therapy to MS. Data indicates that B cells and neutrophils also have significant roles in MS, despite the common belief that T cells are essential. High neutrophil-to-lymphocyte ratios correlate with MS severity, indicating their contribution to disease progression. Dysregulated signaling pathways further exacerbate MS progression.

CONCLUSION

MS remains incurable, but disease-modifying therapies, monoclonal antibodies, and immunomodulatory drugs offer hope for patients. Research on the immunogenetics and immunoregulatory functions of gut microbiota is continuing to provide light on possible treatment avenues. Understanding the complex interplay between genetic predisposition, environmental factors, and immune dysregulation is critical for developing effective treatments for MS.

Dietary ethylenediamine dihydroiodide mitigated Escherichia coli O78-induced immune and intestinal damage of ducks via suppression of NF-κB signal

This study investigated the effect of Ethylenediamine dihydroiodide (EDDI) on growth performance, immune function and intestinal health of meat ducks challenged with Avian pathogenic Escherichia coli (APEC). A total of 360 one-day-old Cherry Valley ducks with similar body weight were randomly allocated to 6 treatments (6 floor cages, 10 birds/cage). A 3 × 2 factor design was used with 3 dietary iodine levels (0, 8, 16 mg/kg in the form EDDI and whether APEC was challenged or not at 7-day-old ducks. The feeding period lasted for 20 d. The results showed that the addition of EDDI reduced APEC-induced decrease of the 20-d weight loss of meat ducks (P < 0.05), and alleviated the inflammatory response of liver tissue induced by APEC challenge in meat ducks. In terms of immune function, EDDI supplementation reduced the immune organ index and increased the immune cell count of meat ducks, reduced the level of endotoxins in the serum of meat ducks (P < 0.05), as well as inhibited the expression levels of liver and spleen inflammatory factors and TLR signaling pathway related genes induced by APEC (P < 0.05). In terms of intestinal health, EDDI inhibited APEC-induced decreases in ZO-3 genes expression and increases in IL-1β and TNF-α expression, increased relative abundance of beneficial bacteria in the cecum and content of metabolites. Pearson correlation analysis showed that there was a significant correlation between liver inflammatory factors and TLR4 signaling pathway genes, and there might be a significant correlation between intestinal microbial flora and other physiological indexes of meat ducks, which indicated that EDDI could reduce the damage to immune function and intestinal health caused by APEC challenge through regulating the structure of intestinal flora. Collectively, our findings suggest that the EDDI can promote growth performance, improve immune function and the intestinal barrier in APEC-challenged meat ducks, which may be related to the suppression of NF-κB signal.

Identification of the C1qDC gene family in grass carp (Ctenopharyngodon idellus) and the response of C1qA, C1qB, and C1qC to GCRV infection in vivo and in vitro

Proteins from the C1q domain-containing (C1qDC) family recognize self-, non-self-, and altered-self ligands and serves as an initiator molecule for the classical complement pathway as well as recognizing immune complexes. In this study, C1qDC gene family members were identified and analyzed in grass carp (Ctenopharyngodon idellus). Members of the C1q subfamily were cloned, and their response to infection with the grass carp virus was investigated. In the grass carp genome, 54 C1qDC genes and 67 isoforms have been identified. Most were located on chromosome 3, with 52 shared zebrafish homologies. Seven substantially differentially expressed C1qDC family genes were identified in the transcriptomes of cytokine-induced killer (CIK) cells infected with grass carp reovirus (GCRV), all of which exhibited sustained upregulation. The opening reading frames of grass carp C1qA, C1qB, and C1qC, belonging to the C1q subfamily, were determined to be 738, 732, and 735 base pairs, encoding 245, 243, and 244 amino acids with molecular weights of 25.81 kDa, 25.63 kDa and 26.16 kDa, respectively. Three genes were detected in the nine collected tissues, and their expression patterns were similar, with the highest expression levels observed in the spleen. In vivo after GCRV infection showed expression trends of C1qA, C1qB, and C1qC in the liver, spleen, and kidney. An N-type pattern in the liver and kidney was characterized by an initial increase followed by a decrease, with the highest expression occurring during the recovering period, and a V-type pattern in the spleen with the lowest expression levels during the death period. In vitro, after GCRV infection showed expression trends of C1qA, C1qB, and C1qC, and this gradually increased within the first 24 h, with a notable increase observed at the 24 h time point. After CIK cells incubation with purified recombinant proteins, rC1qA, rC1qB, and rC1qC for 3 h, followed by GCRV inoculation, the GCRV replication indicated that rC1qC exerted a substantial inhibitory effect on viral replication in CIK cells after 24 h of GCRV inoculation. These findings offer valuable insights into the structure, evolution, and function of the C1qDC family genes and provide a foundational understanding of the immune function of C1q in grass carp.

Humoral immunosuppression of exposure to polycyclic aromatic hydrocarbons and the roles of oxidative stress and inflammation

Previous studies have indicated adverse health effects of exposure to polycyclic aromatic hydrocarbons (PAHs), but evidence on the association between PAH exposure and immunity is scarce and its underlying mechanism is largely unknown. This study assessed human exposure to PAHs by determining the concentrations of PAHs in serum and their metabolites in paired urine. The oxidative stress and inflammation levels were evaluated by urinary DNA damage biomarker 8-hydroxydeoxyguanosine, white blood cell counts and C-reaction protein. We investigated the relationship between PAH exposure and seven immunological components, and explored the indirect roles of oxidative stress and inflammation by mediation and moderation analysis. Multivariate regression analysis revealed that 1-hydroxynaphthalene and 2-hydroxyfluorene were negatively associated with immunoglobulin A, and 3-hydroxyphenanthrene was negatively correlated with complement component 3. Restricted cubic spline analysis demonstrated nonlinear relationships between some individual PAHs or their metabolites with immunological components. Bayesian kernel machine regression and quantile g-computation revealed significant associations of higher PAH exposure with decreased immunoglobulin G and kappa light chain levels. Phenanthrene was the compound that contributed the most to reduced immunoglobulin G. Mediation analysis demonstrated significant indirect effects of 8-hydroxydeoxyguanosine and white blood cell counts on the association between higher PAH exposure and decreased immunological components. Moderation analysis revealed that PAH exposure and decreased immunological components are significantly associated with higher levels of C-reaction protein and white blood cell counts. The results demonstrated significant immunosuppression of PAH exposure and highlighted the indirect roles of oxidative stress and inflammation. Interventions to reduce systemic inflammation may mitigate the adverse immune effects of PAH exposure.

Adjunctive treatments for pneumococcal meningitis: a systematic review of experimental animal models

New treatments are needed to improve the prognosis of pneumococcal meningitis. We performed a systematic review on adjunctive treatments in animal models of pneumococcal meningitis in order to identify treatments with the most potential to progress to clinical trials. Studies testing therapy adjunctive to antibiotics in animal models of pneumococcal meningitis were included. A literature search was performed using Medline, Embase and Scopus for studies published from 1990 up to 17 February 2023. Two investigators screened studies for inclusion and independently extracted data. Treatment effect was assessed on the clinical parameters disease severity, hearing loss and cognitive impairment and the biological parameters inflammation, brain injury and bacterial load. Adjunctive treatments were evaluated by their effect on these outcomes and the quality, number and size of studies that investigated the treatments. Risk of bias was assessed with the SYRCLE risk of bias tool. A total of 58 of 2462 identified studies were included, which used 2703 experimental animals. Disease modelling was performed in rats (29 studies), rabbits (13 studies), mice (12 studies), gerbils (3 studies) or both rats and mice (1 study). Meningitis was induced by injection of Streptococcus pneumoniae into the subarachnoid space. Randomization of experimental groups was performed in 37 of 58 studies (64%) and 12 studies (12%) were investigator-blinded. Overall, 54 treatment regimens using 46 adjunctive drugs were evaluated: most commonly dexamethasone (16 studies), daptomycin (5 studies), complement component 5 (C5; 3 studies) antibody and Mn(III)tetrakis(4-benzoicacid)porphyrin chloride (MnTBAP; 3 studies). The most frequently evaluated outcome parameters were inflammation [32 studies (55%)] and brain injury [32 studies (55%)], followed by disease severity [30 studies (52%)], hearing loss [24 studies (41%)], bacterial load [18 studies (31%)] and cognitive impairment [9 studies (16%)]. Adjunctive therapy that improved clinical outcomes in multiple studies was dexamethasone (6 studies), C5 antibodies (3 studies) and daptomycin (3 studies). HMGB1 inhibitors, matrix metalloproteinase inhibitors, neurotrophins, antioxidants and paquinimod also improved clinical parameters but only in single or small studies. Evaluating the treatment effect of adjunctive therapy was complicated by study heterogeneity regarding the animal models used and outcomes reported. In conclusion, 24 of 54 treatment regimens (44%) tested improved clinically relevant outcomes in experimental pneumococcal meningitis but few were tested in multiple well-designed studies. The most promising new adjunctive treatments are with C5 antibodies or daptomycin, suggesting that these drugs could be tested in clinical trials.

Re-visiting humoral constitutive antibacterial heterogeneity in bloodstream infections

Although cellular immunity has garnered much attention in the era of single-cell technologies, humoral innate immunity has receded in priority due to its presumed limited roles. Hence, despite the long-recognised bactericidal activity of serum-a functional characteristic of constitutive humoral immunity-much remains unclear regarding mechanisms underlying its inter-individual heterogeneity and clinical implications in bloodstream infections. Recent work suggests that the immediate antimicrobial effect of humoral innate immunity contributes to suppression of the excessive inflammatory responses to infection by reducing the amount of pathogen-associated molecular patterns. In this Personal View, we propose the need to re-explore factors underlying the inter-individual heterogeneity in serum antibacterial competence as a new approach to better understand humoral innate immunity and revisit the clinical use of measuring serum antibacterial activity in the management of bacterial bloodstream infections. Given the current emphasis on subtyping sepsis, a serum bactericidal assay might prove useful in defining a distinct sepsis endotype, to enable more personalised management.

What is the role of complement in bystander hemolysis? Old concept, new insights

INTRODUCTION

Bystander hemolysis occurs when antigen-negative red blood cells (RBCs) are lysed by the complement system. Many clinical entities including passenger lymphocyte syndrome, hyperhemolysis following blood transfusion, and paroxysmal nocturnal hemoglobinuria are complicated by bystander hemolysis.

AREAS COVERED

The review provides data about the role of the complement system in the pathogenesis of bystander hemolysis. Moreover, future perspectives on the understanding and management of this syndrome are described.

EXPERT OPINION

Complement system can be activated via classical, alternative, and lectin pathways. Classical pathway activation is mediated by antigen-antibody (autoantibodies and alloantibodies against autologous RBCs, infectious agents) complexes. Alternative pathway initiation is triggered by heme, RBC microvesicles, and endothelial injury that is a result of intravascular hemolysis. Thus, C5b is formed, binds with C6-C9 compomers, and MAC (C5b-9) is formulated in bystander RBCs membranes, leading to cell lysis. Intravascular hemolysis, results in activation of the alternative pathway, establishing a vicious cycle between complement activation and bystander hemolysis. C5 inhibitors have been used effectively in patients with hyperhemolysis syndrome and other entities characterized by bystander hemolysis.

External quality assurance program for diagnostic complement laboratories: evaluation of the results of the past seven years

Introduction

The complement external quality assurance (EQA) program was first organized in 2010 by a group of researchers working in diagnostic complement laboratories. Starting in 2016, INSTAND e.V., a German, non-profit interdisciplinary scientific medical society dedicated to providing expert EQA programs for medical laboratories, started organizing the EQAs for complement diagnostic laboratories together with the same group of experienced scientists and doctors who also work as EQA experts. The aim of the current work is to provide descriptive analysis of the past seven years' complement EQA results and evaluate timeline changes in proficiency testing.

Methods

Each year, in March and October, blinded samples (normal, pathological) were sent to the participating diagnostic laboratories, where complement parameters were evaluated exactly as in daily routine samples. Since no reference method/target values exist for these parameters, and participants used different units for measurement, the reported results were compared to the stable mean (Algorithm A) of the participants using the same method/measurement units. A reported result was qualified as "passed" if it fell into the 30-50% evaluation/target range around the mean of reported results (depending on the given parameter).

Results

While the number of participating laboratories has increased in the past years (from around 120 to 347), the number of complement laboratories providing multiple determinations remained mostly unchanged (around 30 worldwide). C3, C4, C1-inhibitor antigen and activity determinations provided the best proficiency results, with >90% passing quotas in the past years, independent of the applied method. Determination of the functional activity of the three activation pathways was good in general, but results showed large variance, especially with the pathological samples. Complement factor C1q and regulators FH and FI are determined by only a few laboratories, with variable outcomes (in general in the 85-90% pass range). Activation products sC5b-9 and Bb were determined in 30 and 10 laboratories, respectively, with typical passing quotas in the 70-90% range, without a clear tendency over the past years.

Conclusion

With these accumulated data from the past seven years, it is now possible to assess sample-, method-, and evaluation related aspects to further improve proficiency testing and protocolize diagnostic complement determinations.

Free PEG Suppresses Anaphylaxis to PEGylated Nanomedicine in Swine

Covalent conjugation of poly(ethylene glycol) (PEG) is frequently employed to enhance the pharmacokinetics and biodistribution of various protein and nanoparticle therapeutics. Unfortunately, some PEGylated drugs can induce elevated levels of antibodies that can bind PEG, i.e., anti-PEG antibodies (APA), in some patients. APA in turn can reduce the efficacy and increase the risks of allergic reactions, including anaphylaxis. There is currently no intervention available in the clinic that specifically mitigates allergic reactions to PEGylated drugs without the use of broad immunosuppression. We previously showed that infusion of high molecular weight free PEG could safely and effectively suppress the induction of APA in mice and restore prolonged circulation of various PEGylated therapeutics. Here, we explored the effectiveness of free PEG as a prophylaxis against anaphylaxis induced by PEG-specific allergic reactions in swine. Injection of PEG-liposomes (PL) resulted in anaphylactoid shock (pseudoanaphylaxis) within 1-3 min in both naïve and PL-sensitized swine. In contrast, repeated injection of free PEG alone did not result in allergic reactions, and injection of free PEG effectively suppressed allergic reactions to PL, including in previously PL-sensitized swine. These results strongly support the further investigation of free PEG for reducing APA and allergic responses to PEGylated therapeutics.

In a novel autoimmune and high-pressure glaucoma model a complex immune response is induced

Background

The neurodegenerative processes leading to glaucoma are complex. In addition to elevated intraocular pressure (IOP), an involvement of immunological mechanisms is most likely. In the new multifactorial glaucoma model, a combination of high IOP and optic nerve antigen (ONA) immunization leads to an enhanced loss of retinal ganglion cells accompanied by a higher number of microglia/macrophages in the inner retina. Here, we aimed to evaluate the immune response in this new model, especially the complement activation and the number of T-cells, for the first time. Further, the microglia/macrophage response was examined in more detail.

Methods

Six-week-old wildtype (WT+ONA) and βB1-connective tissue growth factor high-pressure mice (CTGF+ONA) were immunized with 1 mg ONA. A wildtype control (WT) and a CTGF group (CTGF) received NaCl instead. Six weeks after immunization, retinae from all four groups were processed for immunohistology, RT-qPCR, and flow cytometry, while serum was used for microarray analyses.

Results

We noticed elevated numbers of C1q+ cells (classical complement pathway) in CTGF and CTGF+ONA retinae as well as an upregulation of C1qa, C1qb, and C1qc mRNA levels in these groups. While the complement C3 was only increased in CTGF and CTGF+ONA retinae, enhanced numbers of the terminal membrane attack complex were noted in all three glaucoma groups. Flow cytometry and RT-qPCR analyses revealed an enhancement of different microglia/macrophages markers, including CD11b, especially in CTGF and CTGF+ONA retinae. Interestingly, increased retinal mRNA as well as serum levels of the tumor necrosis factor α were found throughout the different glaucoma groups. Lastly, more T-cells could be observed in the ganglion cell layer of the new CTGF+ONA model.

Conclusion

These results emphasize an involvement of the complement system, microglia/macrophages, and T-cells in glaucomatous disease. Moreover, in the new multifactorial glaucoma model, increased IOP in combination with autoimmune processes seem to enforce an additional T-cell response, leading to a more persistent pathology. Hence, this new model mimics the pathomechanisms occurring in human glaucoma more accurately and could therefore be a helpful tool to find new therapeutic approaches for patients in the future.

Cancer cells and viruses share common glycoepitopes: exciting opportunities toward combined treatments

Aberrant glycosylation patterns of glycoproteins and glycolipids have long been recognized as one the major hallmarks of cancer cells that has led to numerous glycoconjugate vaccine attempts. These abnormal glycosylation profiles mostly originate from the lack of key glycosyltransferases activities, mutations, over expressions, or modifications of the requisite chaperone for functional folding. Due to their relative structural simplicity, O-linked glycans of the altered mucin family of glycoproteins have been particularly attractive in the design of tumor associated carbohydrate-based vaccines. Several such glycoconjugate vaccine formulations have generated potent monoclonal anti-carbohydrate antibodies useful as diagnostic and immunotherapies in the fight against cancer. Paradoxically, glycoproteins related to enveloped viruses also express analogous N- and O-linked glycosylation patterns. However, due to the fact that viruses are not equipped with the appropriate glycosyl enzyme machinery, they need to hijack that of the infected host cells. Although the resulting N-linked glycans are very similar to those of normal cells, some of their O-linked glycan patterns often share the common structural simplicity to those identified on tumor cells. Consequently, given that both cancer cells and viral glycoproteins share both common N- and O-linked glycoepitopes, glycoconjugate vaccines could be highly attractive to generate potent immune responses to target both conditions.

The role of the complement system in disc degeneration and Modic changes

Disc degeneration and vertebral endplate bone marrow lesions called Modic changes are prevalent spinal pathologies found in chronic low back pain patients. Their pathomechanisms are complex and not fully understood. Recent studies have revealed that complement system proteins and interactors are dysregulated in disc degeneration and Modic changes. The complement system is part of the innate immune system and plays a critical role in tissue homeostasis. However, its dysregulation has also been associated with various pathological conditions such as rheumatoid arthritis and osteoarthritis. Here, we review the evidence for the involvement of the complement system in intervertebral disc degeneration and Modic changes. We found that only a handful of studies reported on complement factors in Modic changes and disc degeneration. Therefore, the level of evidence for the involvement of the complement system is currently low. Nevertheless, the complement system is tightly intertwined with processes known to occur during disc degeneration and Modic changes, such as increased cell death, autoantibody production, bacterial defense processes, neutrophil activation, and osteoclast formation, indicating a contribution of the complement system to these spinal pathologies. Based on these mechanisms, we propose a model how the complement system could contribute to the vicious cycle of tissue damage and chronic inflammation in disc degeneration and Modic changes. With this review, we aim to highlight a currently understudied but potentially important inflammatory pathomechanism of disc degeneration and Modic changes that may be a novel therapeutic target.

Complement C1s deficiency in a male Caucasian patient with systemic lupus erythematosus: a case report

Deficiencies of the early complement components of the classical pathway (CP) are well-documented in association with systemic lupus erythematosus (SLE) or SLE-like syndromes and severe pyogenic infections. Among these, complete C1s deficiency has been reported in nine cases so far. Here, we describe a 34-year-old male patient who presented with severe, recurrent infections since childhood, including meningitides with pneumococci and meningococci, erysipelas, subcutaneous abscess, and recurrent infections of the upper airways. The patient also exhibited adult-onset SLE, meeting 7/11 of the ACR criteria and 34 of the 2019 EULAR/ACR classification criteria, along with class IV-G (A) proliferative lupus nephritis (LN). A screening of the complement cascade showed immeasurably low CH50, while the alternative pathway (AP) function was normal. Subsequent determination of complement components revealed undetectable C1s with low levels of C1r and C1q, normal C3, and slightly elevated C4 and C2 concentrations. The patient had no anti-C1q antibodies. Renal biopsy showed class IV-G (A) LN with complement C1q positivity along the glomerular basement membranes (GBMs) and weak deposition of IgG, IgM, and complement C3 and C4 in the mesangium and GBM. In an ELISA-based functional assay determining C4d deposition, the patient's absent complement activity was fully restored by adding C1s. The genome of the patient was analyzed by whole genome sequencing showing two truncating variants in the C1S gene. One mutation was located at nucleotide 514 in exon 5, caused by a nucleotide substitution from G to T, resulting in a nonsense mutation from Gly172 (p.Gly172*). The other mutation was located at nucleotide 750 in exon 7, where C was replaced by a G, resulting in a nonsense mutation from Tyr250 (p.Tyr250*). Both mutations create a premature stop codon and have not previously been reported in the literature. These genetic findings, combined with the absence of C1s in the circulation, strongly suggest a compound heterozygote C1s deficiency in our patient, without additional defect within the complement cascade. As in a previous C1s deficiency case, the patient responded well to rituximab. The present case highlights unanswered questions regarding the CP's role in SLE etiopathogenesis.

Emerging role of complement in COVID-19 and other respiratory virus diseases

The complement system, a key component of innate immunity, provides the first line of defense against bacterial infection; however, the COVID-19 pandemic has revealed that it may also engender severe complications in the context of viral respiratory disease. Here, we review the mechanisms of complement activation and regulation and explore their roles in both protecting against infection and exacerbating disease. We discuss emerging evidence related to complement-targeted therapeutics in COVID-19 and compare the role of the complement in other respiratory viral diseases like influenza and respiratory syncytial virus. We review recent mechanistic studies and animal models that can be used for further investigation. Novel knockout studies are proposed to better understand the nuances of the activation of the complement system in respiratory viral diseases.

The greatest contribution to medical science is the transformation from studying symptoms to studying their causes-the unrelenting legacy of Robert Koch and Louis Pasteur-and a causality perspective to approach a definition of SLE

The basic initiative related to this study is derived from the fact that systemic lupus erythematosus (SLE) is a unique and fertile system science subject. We are, however, still far from understanding its nature. It may be fair to indicate that we are spending more time and resources on studying the complexity of classified SLE than studying the validity of classification criteria. This study represents a theoretical analysis of current instinctual SLE classification criteria based on "the causality principle." The discussion has its basis on the radical scientific traditions introduced by Robert Koch and Louis Pasteur. They announced significant changes in our thinking of disease etiology through the implementation of the modern version of "the causality principle." They influenced all aspects of today's medical concepts and research: the transformation of medical science from studies of symptoms to study their causes, relevant for monosymptomatic diseases as for syndromes. Their studies focused on bacteria as causes of infectious diseases and on how the immune system adapts to control and prevent contagious spreading. This is the most significant paradigm shift in the modern history of medicine and resulted in radical changes in our view of the immune system. They described acquired post-infection immunity and active immunization by antigen-specific vaccines. The paradigm "transformation" has a great theoretical impact also on current studies of autoimmune diseases like SLE: symptoms and their cause(s). In this study, the evolution of SLE classification and diagnostic criteria is discussed from "the causality principle" perspective, and if contemporary SLE classification criteria are as useful as believed today for SLE research. This skepticism is based on the fact that classification criteria are not selected based on cogent causal strategies. The SLE classification criteria do not harmonize with Koch's and Pasteur's causality principle paradigms and not with Witebsky's Koch-derived postulates for autoimmune and infectious diseases. It is not established whether the classification criteria can separate SLE as a "one disease entity" from "SLE-like non-SLE disorders"-the latter in terms of SLE imitations. This is discussed here in terms of weight, rank, and impact of the classification criteria: Do they all originate from "one basic causal etiology"? Probably not.

Defining Nephritic Factors as Diverse Drivers of Systemic Complement Dysregulation in C3 Glomerulopathy

Introduction

C3 glomerulopathy (C3G) is an ultrarare renal disease characterized by deposition of complement component C3 in the glomerular basement membrane (GBM). Rare and novel genetic variation in complement genes and autoantibodies to complement proteins are commonly identified in the C3G population and thought to drive the underlying complement dysregulation that results in renal damage. However, disease heterogeneity and rarity make accurately defining characteristics of the C3G population difficult.

Methods

Here, we present a retrospective analysis of the Molecular Otolaryngology and Renal Research Laboratories C3G cohort. This study integrated complement biomarker testing and in vitro tests of autoantibody function to achieve the following 3 primary goals: (i) define disease profiles of C3G based on disease drivers, complement biomarkers, and age; (ii) determine the relationship between in vitro autoantibody tests and in vivo complement dysregulation; and (iii) evaluate the association between autoantibody function and disease progression.

Results

The largest disease profiles of C3G included patients with autoantibodies to complement proteins (48%) and patients for whom no genetic and/or acquired drivers of disease could be identified (43%). The correlation between the stabilization of convertases by complement autoantibodies as measured by in vitro modified hemolytic assays and systemic biomarkers that reflect in vivo complement dysregulation was remarkably strong. In patients positive for autoantibodies, the degree of stabilization capacity predicted worse renal function.

Conclusion

This study implicates complement autoantibodies as robust drivers of systemic complement dysregulation in approximately 50% of C3G but also highlights the need for continued discovery-based research to identify novel drivers of disease.

The Role of the Complement in Clear Cell Renal Carcinoma (ccRCC)-What Future Prospects Are There for Its Use in Clinical Practice?

In recent years, the first-line available therapeutic options for metastatic renal cell carcinoma (mRCC) have radically changed with the introduction into clinical practice of new immune checkpoint inhibitor (ICI)-based combinations. Many efforts are focusing on identifying novel prognostic and predictive markers in this setting. The complement system (CS) plays a central role in promoting the growth and progression of mRCC. In particular, mRCC has been defined as an "aggressive complement tumor", which encompasses a group of malignancies with poor prognosie and highly expressed complement components. Several preclinical and retrospective studies have demonstrated the negative prognostic role of the complement in mRCC; however, there is little evidence on its possible role as a predictor of the response to ICIs. The purpose of this review is to explore more deeply the physio-pathological role of the complement in the development of RCC and its possible future use in clinical practice as a prognostic and predictive factor.

Complement System Deficiencies in Elite Athletes

BACKGROUND

Although regular physical activity improves immune competency and reduces the prevalence of inflammatory diseases, strenuous training in elite athletes is associated with an increased susceptibility to infectious complications. Therefore, the objective of our study was to assess the routinely examined parameters of the complement system in elite athletes. The study was carried out in a cohort of elite athletes (n = 134) and healthy control subjects (n = 110). In all subjects, besides a routine laboratory check-up, serum concentrations of the C3 and C4 complement components, mannose-binding lectin (MBL), as well as activation of all three complement pathways were determined.

RESULTS

Compared to healthy controls, lower C3 and C4 complement component concentrations were observed in elite athletes (0.96 ± 0.1 vs. 1.08 ± 0.2 mg/L, and 0.18 ± 0.1 vs. 0.25 ± 0.1 mg/L, respectively, p < 0.05); with much higher frequency rates of C3 and C4 deficiencies in athletes (31.3 vs. 14.5%, and 6 vs. 0%, p < 0.05). Simultaneously, athletes had much higher frequency rates of deficiencies of activation of classical and alternative complement pathways; while, deficiency of activation of the lectin pathway was similar in both cohorts.

CONCLUSIONS

We confirmed a high frequency of defects in the complement system in elite athletes. Lower concentrations of C3 and C4 complement components, with high frequencies of deficiencies of the classical and alternative complement activation pathways were the most prevalent disorder of the complement system in elite athletes. Further studies are needed to uncover the functional impacts of these observations upon the susceptibility to infectious diseases.

Persistent complement dysregulation with signs of thromboinflammation in active Long Covid

Long Covid is a debilitating condition of unknown etiology. We performed multimodal proteomics analyses of blood serum from COVID-19 patients followed up to 12 months after confirmed severe acute respiratory syndrome coronavirus 2 infection. Analysis of >6500 proteins in 268 longitudinal samples revealed dysregulated activation of the complement system, an innate immune protection and homeostasis mechanism, in individuals experiencing Long Covid. Thus, active Long Covid was characterized by terminal complement system dysregulation and ongoing activation of the alternative and classical complement pathways, the latter associated with increased antibody titers against several herpesviruses possibly stimulating this pathway. Moreover, markers of hemolysis, tissue injury, platelet activation, and monocyte-platelet aggregates were increased in Long Covid. Machine learning confirmed complement and thromboinflammatory proteins as top biomarkers, warranting diagnostic and therapeutic interrogation of these systems.

Microbial evasion of the complement system: a continuous and evolving story

The complement system is a fundamental part of the innate immune system that plays a key role in the battle of the human body against invading pathogens. Through its three pathways, represented by the classical, alternative, and lectin pathways, the complement system forms a tightly regulated network of soluble proteins, membrane-expressed receptors, and regulators with versatile protective and killing mechanisms. However, ingenious pathogens have developed strategies over the years to protect themselves from this complex part of the immune system. This review briefly discusses the sequence of the complement activation pathways. Then, we present a comprehensive updated overview of how the major four pathogenic groups, namely, bacteria, viruses, fungi, and parasites, control, modulate, and block the complement attacks at different steps of the complement cascade. We shed more light on the ability of those pathogens to deploy more than one mechanism to tackle the complement system in their path to establish infection within the human host.

The complement cascade in lung injury and disease

BACKGROUND

The complement system is an important arm of immune defense bringing innate and adaptive immunity. Although originally regarded as a major complementary defense mechanism against pathogens, continuously emerging evidence has uncovered a central role of this complex system in several diseases including lung pathologies.

MAIN BODY

Complement factors such as anaphylatoxins C3a and C5a, their receptors C3aR, C5aR and C5aR2 as well as complement inhibitory proteins CD55, CD46 and CD59 have been implicated in pathologies such as the acute respiratory distress syndrome, pneumonia, chronic obstructive pulmonary disease, asthma, interstitial lung diseases, and lung cancer. However, the exact mechanisms by which complement factors induce these diseases remain unclear. Several complement-targeting monoclonal antibodies are reported to treat lung diseases.

CONCLUSIONS

The complement system contributes to the progression of the acute and chronic lung diseases. Better understanding of the underlying mechanisms will provide groundwork to develop new strategy to target complement factors for treatment of lung diseases.

The use of shotgun label-free quantitative proteomic mass spectrometry to evaluate the inflammatory response in aqueous humor from horses with uveitis compared to ophthalmologically healthy horses

OBJECTIVE

The objective of this study was to use shotgun label-free tandem mass spectrometry (LF-MS/MS) to evaluate aqueous humor (AH) from horses with uveitis (UH) compared to ophthalmologically healthy horses (HH).

ANIMALS STUDIED

Twelve horses diagnosed with uveitis based on ophthalmic examination and six ophthalmologically healthy horses (postmortem) purchased for teaching purposes.

PROCEDURES

All horses received a complete ophthalmic examination and physical exam. Aqueous paracentesis was performed on all horses and AH total protein concentrations were measured with nanodrop (TPn) and refractometry (TPr). AH samples were analyzed with shotgun LF-MS/MS and proteomic data were compared between groups using Wilcoxon rank-sum test.

RESULTS

A total of 147 proteins were detected, 11 proteins had higher abundance in UH, and 38 proteins had lower abundance in UH. Proteins with higher abundance included apolipoprotein E, alpha-2-macroglobulin (A2M), alpha-2-HS-glycoprotein, prothrombin, fibrinogen, complement component 4 (C4), joining chain for IgA and IgM, afamin, and amine oxidase. There were positive correlations between TPn (p = .003) and TPr (p = .0001) compared to flare scores.

CONCLUSION

Differential abundance of A2M, prothrombin, fibrinogen, and C4 indicate upregulation of the complement and coagulation cascade in equine uveitis. Proinflammatory cytokines and the complement cascade have potential as therapeutic targets for equine uveitis.

The Role of Innate Immunity in Osteoarthritis and the Connotation of "Immune-joint" Axis: A Narrative Review

Osteoarthritis (OA) is a degenerative disease that results in constriction of the joint space due to the gradual deterioration of cartilage, alterations in subchondral bone, and synovial membrane. Recently, scientists have found that OA involves lesions in the whole joint, in addition to joint wear and tear and cartilage damage. Osteoarthritis is often accompanied by a subclinical form of synovitis, which is a chronic, relatively low-grade inflammatory response mainly mediated by the innate immune system. The "immune-joint" axis refers to an interaction of an innate immune response with joint inflammation and the whole joint range. Previous studies have underestimated the role of the immune-joint axis in OA, and there is no related research. For this reason, this review aimed to evaluate the existing evidence on the influence of innate immune mechanisms on the pathogenesis of OA. The innate immune system is the body's first line of defense. When the innate immune system is triggered, it instantly activates the downstream inflammatory signal pathway, causing an inflammatory response, while also promoting immune cells to invade joint synovial tissue and accelerate the progression of OA. We have proposed the concept of the "immune-joint" axis and explored it from two aspects of Traditional Chinese Medicine (TCM) theory and modern medical research, such as the innate immunity and OA, macrophages and OA, complement and OA, and other cells and OA, to enrich the scientific connotation of the "immune-joint" axis.