The C1q and gC1qR axis as a novel checkpoint inhibitor in cancer

Understanding at the molecular level of the cell biology of tumors has led to significant treatment advances in the past. Despite such advances however, development of therapy resistance and tumor recurrence are still unresolved major challenges. This therefore underscores the need to identify novel tumor targets and develop corresponding therapies to supplement existing biologic and cytotoxic approaches so that a deeper and more sustained treatment responses could be achieved. The complement system is emerging as a potential novel target for cancer therapy. Data accumulated to date show that complement proteins, and in particular C1q and its receptors cC1qR/CR and gC1qR/p33/HABP1, are overexpressed in most cancer cells and together are involved not only in shaping the inflammatory tumor microenvironment, but also in the regulation of angiogenesis, metastasis, and cell proliferation. In addition to the soluble form of C1q that is found in plasma, the C1q molecule is also found anchored on the cell membrane of monocytes, macrophages, dendritic cells, and cancer cells, via a 22aa long leader peptide found only in the A-chain. This orientation leaves its 6 globular heads exposed outwardly and thus available for high affinity binding to a wide range of molecular ligands that enhance tumor cell survival, migration, and proliferation. Similarly, the gC1qR molecule is not only overexpressed in most cancer types but is also released into the microenvironment where it has been shown to be associated with cancer cell proliferation and metastasis by activation of the complement and kinin systems. Co-culture of either T cells or cancer cells with purified C1q or anti-gC1qR has been shown to induce an anti-proliferative response. It is therefore postulated that in the tumor microenvironment, the interaction between C1q expressing cancer cells and gC1qR bearing cytotoxic T cells results in T cell suppression in a manner akin to the PD-L1 and PD-1 interaction.

Crystal structure of Trichinella spiralis calreticulin and the structural basis of its complement evasion mechanism involving C1q

Helminths produce calreticulin (CRT) to immunomodulate the host immune system as a survival strategy. However, the structure of helminth-derived CRT and the structural basis of the immune evasion process remains unclarified. Previous study found that the tissue-dwelling helminth Trichinella spiralis produces calreticulin (TsCRT), which binds C1q to inhibit activation of the complement classical pathway. Here, we used x-ray crystallography to resolve the structure of truncated TsCRT (TsCRTΔ), the first structure of helminth-derived CRT. TsCRTΔ was observed to share the same binding region on C1q with IgG based on the structure and molecular docking, which explains the inhibitory effect of TsCRT on C1q-IgG-initiated classical complement activation. Based on the key residues in TsCRTΔ involved in the binding activity to C1q, a 24 amino acid peptide called PTsCRT was constructed that displayed strong C1q-binding activity and inhibited C1q-IgG-initiated classical complement activation. This study is the first to elucidate the structural basis of the role of TsCRT in immune evasion, providing an approach to develop helminth-derived bifunctional peptides as vaccine target to prevent parasite infections or as a therapeutic agent to treat complement-related autoimmune diseases.

Fc-engineered antibodies with immune effector functions completely abolished

Elimination of the binding of immunoglobulin Fc to Fc gamma receptors (FcγR) is highly desirable for the avoidance of unwanted inflammatory responses to therapeutic antibodies and fusion proteins. Many different approaches have been described in the literature but none of them completely eliminates binding to all of the Fcγ receptors. Here we describe a set of novel variants having specific amino acid substitutions in the Fc region at L234 and L235 combined with the substitution G236R. They show no detectable binding to Fcγ receptors or to C1q, are inactive in functional cell-based assays and do not elicit inflammatory cytokine responses. Meanwhile, binding to FcRn, manufacturability, stability and potential for immunogenicity are unaffected. These variants have the potential to improve the safety and efficacy of therapeutic antibodies and Fc fusion proteins.

Development and Characterization of a Multiplex Assay to Quantify Complement-Fixing Antibodies against Dengue Virus

Antibodies capable of activating the complement system (CS) when bound with antigen are referred to as "complement-fixing antibodies" and are involved in protection against Flaviviruses. A complement-fixing antibody test has been used in the past to measure the ability of dengue virus (DENV)-specific serum antibodies to activate the CS. As originally developed, the test is time-consuming, cumbersome, and has limited sensitivity for DENV diagnosis. Here, we developed and characterized a novel multiplex anti-DENV complement-fixing assay based on the Luminex platform to quantitate serum antibodies against all four serotypes (DENV1-4) that activate the CS based on their ability to fix the complement component 1q (C1q). The assay demonstrated good reproducibility and showed equivalent performance to a DENV microneutralization assay that has been used to determine DENV serostatus. In non-human primates, antibodies produced in response to primary DENV1-4 infection induced C1q fixation on homologous and heterologous serotypes. Inter-serotype cross-reactivity was associated with homology of the envelope protein. Interestingly, the antibodies produced following vaccination against Zika virus fixed C1q on DENV. The anti-DENV complement fixing antibody assay represents an alternative approach to determine the quality of functional antibodies produced following DENV natural infection or vaccination and a biomarker for dengue serostatus, while providing insights about immunological cross-reactivity among different Flaviviruses.

Amyloid beta acts synergistically as a pro-inflammatory cytokine

The amyloid beta (Aβ) peptide is believed to play a central role in Alzheimer's disease (AD), the most common age-related neurodegenerative disorder. However, the natural, evolutionarily selected functions of Aβ are incompletely understood. Here, we report that nanomolar concentrations of Aβ act synergistically with known cytokines to promote pro-inflammatory activation in primary human astrocytes (a cell type increasingly implicated in brain aging and AD). Using transcriptomics (RNA-seq), we show that Aβ can directly substitute for the complement component C1q in a cytokine cocktail previously shown to induce astrocyte immune activation. Furthermore, we show that astrocytes synergistically activated by Aβ have a transcriptional signature similar to neurotoxic "A1" astrocytes known to accumulate with age and in AD. Interestingly, we find that this biological action of Aβ at low concentrations is distinct from the transcriptome changes induced by the high/supraphysiological doses of Aβ often used in in vitro studies. Collectively, our results suggest an important, cytokine-like function for Aβ and a novel mechanism by which it may directly contribute to the neuroinflammation associated with brain aging and AD.

A 56-Year-Old Man With Emphysema, Rash, and Arthralgia

CASE PRESENTATION

A 56-year-old man presented to the pulmonary clinic with dyspnea and hypoxemia on exertion. He was an avid biker and skier who had noticed a significant decrease in high-level physical activity over the past 3 years. He reported dyspnea, desaturations at altitudes higher than 9,000 feet, dry cough, tachycardia, and palpitations with exercise. Review of systems was also notable for gluten-intolerance, Raynaud's phenomenon, recurrent skin lesions and joint swelling, pain, and stiffness in the areas overlying the jaw, wrists, knees, and ankles (after capsaicin exposure). He denied fever, chills, anorexia, weight loss, hair loss, ocular symptoms, jaw claudication, chest pain, or lower extremity swelling. He had a five pack-year smoking history, no history of prematurity, childhood asthma, recurrent infections, or environmental and occupational exposure. Based on pulmonary function tests from an outside provider, he had received a diagnosis of exercise-induced asthma and had been prescribed an albuterol inhaler to use on an as-needed basis, which failed to improve his symptoms. He was later prescribed a mometasone-formoterol inhaler, still with no symptomatic improvement.

Retinal Ganglion Cell Axon Regeneration Requires Complement and Myeloid Cell Activity within the Optic Nerve

Axon regenerative failure in the mature CNS contributes to functional deficits following many traumatic injuries, ischemic injuries, and neurodegenerative diseases. The complement cascade of the innate immune system responds to pathogen threat through inflammatory cell activation, pathogen opsonization, and pathogen lysis, and complement is also involved in CNS development, neuroplasticity, injury, and disease. Here, we investigated the involvement of the classical complement cascade and microglia/monocytes in CNS repair using the mouse optic nerve injury (ONI) model, in which axons arising from retinal ganglion cells (RGCs) are disrupted. We report that central complement C3 protein and mRNA, classical complement C1q protein and mRNA, and microglia/monocyte phagocytic complement receptor CR3 all increase in response to ONI, especially within the optic nerve itself. Importantly, genetic deletion of C1q, C3, or CR3 attenuates RGC axon regeneration induced by several distinct methods, with minimal effects on RGC survival. Local injections of C1q function-blocking antibody revealed that complement acts primarily within the optic nerve, not retina, to support regeneration. Moreover, C1q opsonizes and CR3+ microglia/monocytes phagocytose growth-inhibitory myelin debris after ONI, a likely mechanism through which complement and myeloid cells support axon regeneration. Collectively, these results indicate that local optic nerve complement-myeloid phagocytic signaling is required for CNS axon regrowth, emphasizing the axonal compartment and highlighting a beneficial neuroimmune role for complement and microglia/monocytes in CNS repair.SIGNIFICANCE STATEMENT Despite the importance of achieving axon regeneration after CNS injury and the inevitability of inflammation after such injury, the contributions of complement and microglia to CNS axon regeneration are largely unknown. Whereas inflammation is commonly thought to exacerbate the effects of CNS injury, we find that complement proteins C1q and C3 and microglia/monocyte phagocytic complement receptor CR3 are each required for retinal ganglion cell axon regeneration through the injured mouse optic nerve. Also, whereas studies of optic nerve regeneration generally focus on the retina, we show that the regeneration-relevant role of complement and microglia/monocytes likely involves myelin phagocytosis within the optic nerve. Thus, our results point to the importance of the innate immune response for CNS repair.

Characterisation and functional role of a novel C1qDC protein from a colonial ascidian

As an invertebrate, the compound ascidian Botryllus schlosseri faces nonself only with innate immunity. In this species, we already identified the key components of the lectin and alternative complement activation pathways. In the present work, by mining the transcriptome, we identified a single transcript codifying for a protein, member of the C1q-domain-containing protein family, with a signal peptide followed by two globular C1q (gC1q) domains. It shares a similar domain organisation with C1q/TNF-related proteins 4, the only vertebrate protein family with two gC1q domains. Our gC1q domain-containing protein, called BsC1qDC, is actively transcribed by immunocytes. The transcription is modulated during the Botryllus blastogenetic cycle and is upregulated following the injection of Bacillus clausii cells in the circulation. Furthermore, the injection of bsc1qdc iRNA in the vasculature results in decreased transcription of the gene and a significant impairment of phagocytosis and degranulation, suggesting the involvement of this molecule in immune responses.

The Spectrum of C4d Deposition in Renal Biopsies of Lupus Nephritis Patients

Objectives

This study aimed to determine the prevalence and localization of complement factor C4d in renal biopsies from patients with lupus nephritis (LN), as well as its associations with the disease's clinico-pathological features. The correlation between arteriolar C4d deposition and renal microvascular lesions (RVLs) was further analyzed.

Methods

A total of 325 biopsy-proven LN patients were enrolled, and their clinico-pathological data were collected. C4d staining of renal biopsies was performed by immunohistochemistry. The associations between C4d deposition and the clinico-pathological features were further analyzed.

Results

C4d deposition was present in most (98.8%) renal specimens in our cohort. These deposits were localized in the glomeruli (98.2%), tubular basement membrane (TBM) (43.7%), arterioles (31.4%), and peritubular capillary (33.8%). Patients with TBM C4d staining had higher disease activity (measured with the Systemic Lupus Erythematous Disease Activity Index) and higher National Institutes of Health pathological activity and chronicity indices (all P < 0.01). Patients with arteriolar C4d deposition were more likely to develop RVLs (91.2%) compared to those with no arteriolar C4d deposition (78.0%; P = 0.004), especially with two or more types of RVLs (P < 0.001). During the mean follow-up of 55.8 months, arteriolar C4d was related to worse renal outcomes [hazard ration (HR): 2.074, 95% confidence interval (CI) 1.056-4.075, P = 0.034]. Multivariate Cox hazard analysis showed that co-deposition of arteriolar C4d and C3c was an independent risk factor (HR: 3.681, 95% CI 1.519-8.921, P = 0.004) for predicting renal outcomes.

Conclusions

C4d deposition was common in renal tissues from LN patients. TBM C4d deposition was related to the disease activity, and arteriolar C4d deposition was associated with RVLs and worse renal outcomes.

Serum IgG2 antibody multicomposition in systemic lupus erythematosus and lupus nephritis (Part 1): cross-sectional analysis

OBJECTIVES

Serum anti-dsDNA and anti-nucleosome IgGs have been proposed as signatures for SLE and LN in limited numbers of patients. We sought to show higher sensitivity and specificity of the same antibodies with the IgG2 isotype and included IgG2 antibodies vs specific intracellular antigens in the analysis.

METHODS

A total of 1052 SLE patients with (n = 479) and without (n = 573) LN, recruited at different times from the beginning of symptoms, were included in the study. Patients with primary APS (PAPS, n = 24), RA (RA, n = 24) and UCTD (UCTD, n = 96) were analysed for comparison. Anti-nucleosome (dsDNA, Histone2A, Histone3), anti-intracellular antigens (ENO1), anti-annexin A1 and anti-C1q IgG2 were determined by non-commercial techniques.

RESULTS

The presence in the serum of the IgG2 panel was highly discriminatory for SLE/LN vs healthy subjects. Serum levels of anti-dsDNA and anti-C1q IgG2 were more sensitive than those of IgGs (Farr radioimmunoassay/commercial assays) in identifying SLE patients at low-medium increments. Of more importance, serum positivity for anti-ENO1 and anti-H2A IgG2 discriminated between LN and SLE (ROC T0-12 months), and high levels at T0-1 month were detected in 63% and 67%, respectively, of LN, vs 3% and 3%, respectively, of SLE patients; serum positivity for each of these was correlated with high SLEDAI values. Minor differences existed between LN/SLE and the other rheumatologic conditions.

CONCLUSION

Nephritogenic IgG2 antibodies represent a specific signature of SLE/LN, with a few overlaps with other rheumatologic conditions. High levels of anti-ENO1 and anti-H2A IgG2 correlated with SLE activity indexes and were discriminatory between SLE patients limited to the renal complication and other SLE patients.

TRIAL REGISTRATION

The Zeus study was registered at https://clinicaltrials.gov, NCT02403115.

Inflammatory and Oxidative Pathways Are New Drug Targets in Multiple Episode Schizophrenia and Leaky Gut, Klebsiella pneumoniae, and C1q Immune Complexes Are Additional Drug Targets in First Episode Schizophrenia

Breakdown of paracellular and vascular pathways and activated neuroimmune and oxidative pathways was established in (deficit) schizophrenia. The aim of this study was to delineate (a) the differences in these pathways between stable-phase, first (FES) and multiple (MES) episode schizophrenia and (b) the pathways that determine the behavioral-cognitive-physical-psychosocial (BCPS) deterioration in FES/MES. This study included 21 FES and 58 FES patients and 40 healthy controls and measured indicants of serum C1q circulating immune complexes (CIC), leaky gut, immune activation, and oxidative stress toxicity (OSTOX). We constructed a BCPS-worsening index by extracting a latent vector from symptomatic, neurocognitive, and quality of life data. FES was associated with higher IgA CIC-C1q, IgA directed to cadherin, catenin, and plasmalemma vesicle-associated protein, and IgA/IgM to Gram-negative bacteria as compared with FES and controls. In FES patients, the BCPS-worsening score was predicted (48.7%) by IgA to Klebsiella pneumoniae and lowered paraoxonase 1 activity. In MES patients, the BCPS-worsening score was explained (42.7%) by increased tumor necrosis factor-α, OSTOX, and number of episodes. In schizophrenia, 34.0% of the variance in the BCPS-worsening score was explained by IgA to K. pneumoniae, OSTOX, and number of episodes. Increased IgA to K. pneumoniae was the single best predictor of residual psychotic symptoms in FES and MES. This study delineated different mechanistic processes in FES, including breakdown of adherens junctions, bacterial translocation, and IgA CIC-C1q formation, and MES, including immune and oxidative neurotoxic pathways. FES and MES comprise different staging subtypes, i.e., FES and MES with and without worsening.

Serum IgG2 antibody multi-composition in systemic lupus erythematosus and in lupus nephritis (Part 2): prospective study

OBJECTIVES

Circulating anti-ENO1 and anti-H2A IgG2 have been identified as specific signatures of LN in a cross-over approach. We sought to show whether the same antibodies identify selected population of patients with LN with potentially different clinical outcomes.

METHODS

Here we report the prospective analysis over 36 months of circulating IgG2 levels in patients with newly diagnosed LN (n=91) and SLE (n=31) and in other patients with SLE recruited within 2 years from diagnosis (n=99). Anti-podocyte (ENO1), anti-nucleosome (DNA, histone 2 A, histone 3) and anti-circulating proteins (C1q, AnnexinA1-ANXA1) IgG2 antibodies were determined by home-made techniques.

RESULTS

LN patients were the main focus of the study. Anti-ENO1, anti-H2A and anti-ANXA1 IgG2 decreased in parallel to proteinuria and normalized within 12 months in the majority of patients while anti-dsDNA IgG2 remained high over the 36 months. Anti-ENO1 and anti-H2A had the highest association with proteinuria (Heat Map) and identified the highest number of patients with high proteinuria (68% and 71% respectively) and/or with reduced estimated glomerula filtration rate (eGFR) (58% for both antibodies) compared with 23% and 17% of anti-dsDNA (agreement analysis). Anti-ENO1 positive LN patients had higher proteinuria than negative patients at T0 and presented the maximal decrement within 12 months.

CONCLUSIONS

Anti-ENO1, anti-H2A and anti-ANXA1 antibodies were associated with high proteinuria in LN patients and Anti-ENO1 also presented the maximal reduction within 12 months that paralleled the decrease of proteinuria. Anti-dsDNA were not associated with renal outcome parameters. New IgG2 antibody signatures should be utilized as tracers of personalized therapies in LN.

TRIAL REGISTRATION

The Zeus study was registered at https://clinicaltrials.gov (study number: NCT02403115).

Antibodies Against the NH2-Terminus of the GluA Subunits Affect the AMPA-Evoked Releasing Activity: The Role of Complement

Antibodies recognizing the amino-terminal domain of receptor subunit proteins modify the receptor efficiency to controlling transmitter release in isolated nerve endings (e.g., synaptosomes) indirectly confirming their presence in these particles but also allowing to speculate on their subunit composition. Western blot analysis and confocal microscopy unveiled the presence of the GluA1, GluA2, GluA3, and GluA4 receptor subunits in cortical synaptosomes. Functional studies confirmed the presence of presynaptic release-regulating AMPA autoreceptors in these terminals, whose activation releases [3H]D-aspartate ([3H]D-Asp, here used as a marker of glutamate) in a NBQX-dependent manner. The AMPA autoreceptors traffic in a constitutive manner, since entrapping synaptosomes with the pep2-SVKI peptide (which interferes with the GluA2-GRIP1/PICK1 interaction) amplified the AMPA-evoked releasing activity, while the inactive pep2-SVKE peptide was devoid of activity. Incubation of synaptosomes with antibodies recognizing the NH2 terminus of the GluA2 and the GluA3 subunits increased, although to a different extent, the GluA2 and 3 densities in synaptosomal membranes, also amplifying the AMPA-evoked glutamate release in a NBQX-dependent fashion. We then analyzed the releasing activity of complement (1:300) from both treated and untreated synaptosomes and found that the complement-induced overflow occurred in a DL-t-BOA-sensitive, NBQX-insensitive fashion. We hypothesized that anti-GluA/GluA complexes in neuronal membranes could trigger the classic pathway of activation of the complement, modifying its releasing activity. Accordingly, the complement-evoked release of [3H]D-Asp from antiGluA2 and anti-GluA3 antibody treated synaptosomes was significantly increased when compared to untreated terminals and facilitation was prevented by omitting the C1q component of the immunocomplex. Antibodies recognizing the NH2 terminus of the GluA1 or the GluA4 subunits failed to affect both the AMPA and the complement-evoked tritium overflow. Our results suggest the presence of GluA2/GluA3-containing release-regulating AMPA autoreceptors in cortical synaptosomes. Incubation of synaptosomes with commercial anti-GluA2 or anti-GluA3 antibodies amplifies the AMPA-evoked exocytosis of glutamate through a complement-independent pathway, involving an excessive insertion of AMPA autoreceptors in plasma membranes but also affects the complement-dependent releasing activity, by promoting the classic pathway of activation of the immunocomplex. Both events could be relevant to the development of autoimmune diseases typified by an overproduction of anti-GluA subunits.

Neurotoxic microglia promote TDP-43 proteinopathy in progranulin deficiency

Aberrant aggregation of the RNA-binding protein TDP-43 in neurons is a hallmark of frontotemporal lobar degeneration caused by haploinsufficiency in the gene encoding progranulin1,2. However, the mechanism leading to TDP-43 proteinopathy remains unclear. Here we use single-nucleus RNA sequencing to show that progranulin deficiency promotes microglial transition from a homeostatic to a disease-specific state that causes endolysosomal dysfunction and neurodegeneration in mice. These defects persist even when Grn-/- microglia are cultured ex vivo. In addition, single-nucleus RNA sequencing reveals selective loss of excitatory neurons at disease end-stage, which is characterized by prominent nuclear and cytoplasmic TDP-43 granules and nuclear pore defects. Remarkably, conditioned media from Grn-/- microglia are sufficient to promote TDP-43 granule formation, nuclear pore defects and cell death in excitatory neurons via the complement activation pathway. Consistent with these results, deletion of the genes encoding C1qa and C3 mitigates microglial toxicity and rescues TDP-43 proteinopathy and neurodegeneration. These results uncover previously unappreciated contributions of chronic microglial toxicity to TDP-43 proteinopathy during neurodegeneration.

Development of the clinical candidate PBD-C06, a humanized pGlu3-Aβ-specific antibody against Alzheimer's disease with reduced complement activation

In clinical trials with early Alzheimer's patients, administration of anti-amyloid antibodies reduced amyloid deposits, suggesting that immunotherapies may be promising disease-modifying interventions against Alzheimer's disease (AD). Specific forms of amyloid beta (Aβ) peptides, for example post-translationally modified Aβ peptides with a pyroglutamate at the N-terminus (pGlu3, pE3), are attractive antibody targets, due to pGlu3-Aβ's neo-epitope character and its propensity to form neurotoxic oligomeric aggregates. We have generated a novel anti-pGlu3-Aβ antibody, PBD-C06, which is based on a murine precursor antibody that binds with high specificity to pGlu3-Aβ monomers, oligomers and fibrils, including mixed aggregates of unmodified Aβ and pGlu3-Aβ peptides. PBD-C06 was generated by first grafting the murine antigen binding sequences onto suitable human variable light and heavy chains. Subsequently, the humanized antibody was de-immunized and site-specific mutations were introduced to restore original target binding, to eliminate complement activation and to improve protein stability. PBD-C06 binds with the same specificity and avidity as its murine precursor antibody and elimination of C1q binding did not compromise Fcγ-receptor binding or in vitro phagocytosis. Thus, PBD-C06 was specifically designed to target neurotoxic aggregates and to avoid complement-mediated inflammatory responses, in order to lower the risk for vasogenic edemas in the clinic.

Complement C1q subunit molecules from Xenopus laevis possess conserved function in C1q-immunoglobulin interaction

Complement component 1q (C1q), together with C1r and C1s to form C1, recognize and bind immune complex to initiate the classical complement pathway. In this study, C1q subunit molecules (XlC1qA, XlC1qB, XlC1qC) were cloned and analyzed from Xenopus laevis (X. laevis). The open reading frame (ORF) of XlC1qA is 819 bp of nucleotide sequence encoding 272 amino acids, the ORF of XlC1qB is 711 bp encoding 236 aa, and the XlC1qC is consists of 732 bp encoding 243 aa. The deduced amino acid sequences contain a collagen-like region (CLR), Gly-X-Y repeats in the N-terminus and a C1q family domain at the C-terminus. Phylogenetic analysis revealed that the XlC1qs are clustered with the amphibian clade. Expression analysis indicated that the XlC1qs exhibited constitutive expression in all examined tissues, with the highest expression in liver. Additionally, XlC1q could interact with heat-aggregated mouse IgG and IgM, Xenopus IgM and Nile tilapia IgM, respectively, indicating the functional conservation of XlC1q binding to immunoglobulins. Further, XlC1qs can inhibit C1q-dependent hemolysis of sensitized sheep red blood cells with concentration-dependent manner. These data collectively suggest that the function of C1qs in X. laevis may be conserved in interaction with immunoglobulins, as that of mammals and teleosts.

A C1qDC (CgC1qDC-6) with a collagen-like domain mediates hemocyte phagocytosis and migration in oysters

Most of the bivalve C1q domain containing proteins (C1qDCs) are either only composed of the globular head domain, or contain an N-terminal coiled-coil domain, presumed to cover a role in oligomerization. On the other hand, collagen regions, widespread in vertebrate C1qDCs, are very uncommon in bivalves. In the present study, a C1qDC with a collagen-like domain (designated CgC1qDC-6) was identified from the Pacific oyster Crassostrea gigas and its possible involvement in immune responses was also characterized. The coding sequence of CgC1qDC-6 was of 756 bp, encoding a peptide of 251 amino acids with an N-terminal signal peptide, a central collagen-like domain, and a C-terminal ghC1q domain. CgC1qDC-6 was clustered with the C1qDCs from several mollusks in the phylogenetic tree. CgC1qDC-6 was detected at both mRNA and protein levels in all tested tissues including hepatopancreas, gonad, gill, mantle, adductor muscle, and hemocytes. The recombinant CgC1qDC-6 protein (rCgC1qDC-6) exhibited binding activity to various pathogen-associated molecular patterns (PAMPs) including LPS, PGN, mannose and Poly I:C, and microorganisms including Gram-negative bacteria (Escherichia coli and Vibrio splendidus), Gram-positive bacteria (Micrococcus luteus and Staphylococcus aureus), and fungus (Pichia pastoris). The phagocytic rates of oyster hemocytes towards V. splendidus pre-incubation with rCgC1qDC-6 were significantly enhanced (p < 0.05). In the chemotaxis assay, rCgC1qDC-6 could mediate the migration of oyster hemocytes in a dose-dependent manner, which exhibited a positive chemotactic effect at low concentration (<10 nM). These results collectively indicated that CgC1qDC-6 could serve as a pattern recognition receptor and mediate the hemocyte phagocytosis and migration to eliminate the invading pathogens.

Hemolymph C1qDC promotes the phagocytosis of oyster Crassostrea gigas hemocytes by interacting with the membrane receptor β-integrin

Phagocytosis constitutes a conserved cellular process for multicellular animals to ingest or engulf other cells or particles, which is facilitated by the use of opsonins to bind foreign particles and interact with cell surface receptors. The invertebrate secreted C1q domain-containing proteins (C1qDCs) have been reported to exhibit opsonic activity, while the detailed mechanisms of opsonization still remain unclear. In the present study, a C1qDC (designated as CgC1qDC-5) with opsonic activity was identified from the hemolymph of oyster Crassostrea gigas. CgC1qDC-5 exhibited the ability to bind pathogen-associated molecular patterns (PAMPs) of lipopolysaccharides (LPS) and Lipid A. It could also bind and agglutinate Gram-negative bacteria Escherichia coli, Vibrio splendidus and Vibrio anguillarum, whereas the agglutinating activity could be inhibited by LPS. In addition, CgC1qDC-5 could enhance the phagocytosis of hemocytes toward E. coli, V. splendidus, and V. anguillarum. GST pull-down and surface plasmon resonance assays in vitro revealed that CgC1qDC-5 could interact with β-integrin (CgIntegrin). In vivo, CgC1qDC-5 was observed to bind hemocytes and co-localized with CgIntegrin on the cell membrane of hemocytes. Antibody-mediated blockage of CgIntegrin hindered the CgC1qDC-5-enhanced hemocytic phagocytosis. CgIntegrin also exhibited the ability to bind the Gram-negative bacteria E. coli, V. splendidus, V. anguillarum and Vibrio parahaemolyticus, and PAMP of LPS, but not Lipid A. A phagocytosis assay demonstrated that CgIntegrin could directly mediate phagocytosis toward bacteria as a phagocytic receptor. These results collectively suggested that CgC1qDC-5 could serve as an opsonin to recognize and bind bacteria, and subsequently interact with CgIntegrin on the hemocyte surface to enhance the CgIntegrin-mediated phagocytosis in oyster.

Investigation of Anti-HLA Antibodies of Highly Sensitized Patients by Single Antigen Bead and C1q Tests

PURPOSE

The single antigen bead (SAB) test contributes to conventional cellular and solid phase crossmatch tests in renal transplantation. However, the determination of anti-HLA antibodies of the patients may not reflect the pathologic features of these antibodies. Highly sensitized patients produce antibodies against a number of HLAs; therefore, their transplantation chance decreases. In this study, we aimed to evaluate SAB and C1q test results of highly sensitized patients.

METHOD

In this study, 33 end-stage renal failure patients with >80% panel reactive antibody were included. Of the patients, 58% (n = 19) were female, and 42% (n = 14) were male. The mean age was 46.2 ± 12.4. All of the serum samples were inactivated by heat before use. SAB and C1q tests were performed according to the manufacturer's instructions.

RESULTS

We obtained statistically significant results between the positive bead counts and raw mean fluorescence intensity (MFI) values of 2 tests (P < .01 for class I and II). There was a statistically significant difference between the 2 tests in terms HLA-A, -C, -DR, and -DP MFI values, whereas HLA-B and -DQ MFI values were similar for the 2 tests.

CONCLUSION

The difference of raw MFI values between the 2 tests may be due to the fact that the C1q test detects only IgG1 and IgG3 antibodies, whereas the SAB test can detect all IgG subtypes. We considered that anti-HLA-B and -DQ antibodies have high complement-fixing features; these antibodies should be investigated selectively due to the similarity of anti-HLA-B and -DQ antibody MFI values in the 2 tests.

Identification of a novel C1q complement component in razor clam Sinonovacula constricta and its role in antibacterial activity

The serum complement component C1q mediates a variety of immune regulatory functions. Herein, we identified a globular head C1q (ghC1q) gene in razor clam Sinonovacula constricta. The complete Sc-ghC1q gene was 872 bp long included an 81 bp 5'-untranslated region (UTR), a 95 bp 3'-UTR with a poly(A) tail, and an open reading frame (ORF) of 696 bp. The mRNA expression of Sc-ghC1q was upregulated in hepatopancreas and hemocytes. After Staphylococcus aureus or Vibrio anguillarum challenge, Sc-ghC1q mRNA transcript abundance was significantly upregulated in hemolymph. Recombinant Sc-ghC1q protein could bind lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and it could agglutinate both Gram-positive and Gram-negative bacteria. Additionally, flow cytometry revealed that Sc-ghC1q strongly promoted phagocytosis in hemocytes. Together, these results demonstrated that Sc-ghC1q played an important role in innate immunity in S. constricta.

A novel C1q domain containing protein in black rockfish (Sebastes schlegelii) serves as a pattern recognition receptor with immunoregulatory properties and possesses binding activity to heat-aggregated IgG

C1q-domain-containing (C1qDC) proteins, which are involved in a series of immune responses, are important pattern recognition receptors in innate immunity in vertebrates and invertebrates. Functional studies of C1qDC proteins in vertebrates are scarce. In the present study, a C1qDC protein (SsC1qDC) from the teleost black rockfish (Sebastes schlegelii) was identified and examined at expression and functional levels. The open reading frame of SsC1qDC is 636 bp, and the predicted amino acid sequence of SsC1qDC shares 62%-69% overall identity with the C1qDC proteins of several fish species. SsC1qDC possesses conserved C1qDC features, including a signal sequence and a C1q domain. SsC1qDC was expressed in different tissues and its expression was up-regulated by bacterial and viral infection. Recombinant SsC1qDC (rSsC1qDC) exhibited apparent binding activities against PAMPs including LPS and PGN. rSsC1qDC had antibacterial activity against Vibrio parahaemolyticus, and was able to enhance the phagocytic activity of macrophages towards Vibrio anguillarum. rSsC1qDC interacted with human heat-aggregated IgG. Furthermore, in the presence of rSsC1qDC, fish exhibited enhanced resistance against bacterial infection. Collectively, these results indicated that SsC1qDC serves as a pattern recognition receptor and plays a vital role in the defense system of black rockfish.

Characterization and functional analysis of a novel gC1qR in the swimming crab Portunus trituberculatus

The receptor for the globular head of complement component C1q, gC1qR, is a multifunctional and multiligand binding protein with a crucial role in host defense. In the present study, a full-length cDNA sequence of a gC1qR homolog (PtgC1qR) in Portunus trituberculatus was identified. PtgC1qR was a 268-amino-acid polypeptide with a conserved MAM33 domain and a mitochondrial targeting sequence in the first 56 amino acids. The transcripts of PtgC1qR were detected in all examined tissues with the highest level detected in the hepatopancreas. Compared with other early embryonic stages, PtgC1qR was highly expressed in the fertilized eggs and embryos at the cleavage stage, which suggest PtgC1qR may be a maternal gene. The transcripts of PtgC1qR in hemocytes exhibited time-dependent response expression pattern after challenged with bacteria (Vibrio alginolyticus, Micrococcus luteus) and fungi (Pichia pastoris). Moreover, the recombinant PtgC1qR (rPtgC1qR) exhibited strong antibacterial activity and microbial-binding activity, suggesting its crucial role in immune defense and recognition. Further phenoloxidase (PO) assay showed that rPtgC1qR could suppress the crab PO activity in vitro in a dose-dependent manner, and it could result in nearly 100% inhibition of PO activity under the concentration of 11.65 μM. Knockdown of PtgC1qR could significantly enhance the expression of serine protease related genes (PtSP1-3 and PtSPH), proPO-associated genes (PtproPO and PtPPAF) and C3-like genes (Ptα2M1 and PtTEP). However, the phagocytosis related genes (PtMyosin, PtRab5 and PtArp) and Ptα2M2 were significantly down-regulated in the PtgC1qR silenced crabs. These findings together demonstrate that PtgC1qR might function in crab immune response via its antibacterial activity, immune recognition or regulating the proPO system, complement pathway and phagocytosis.

A novel globular C1q domain containing protein (C1qDC-7) from Crassostrea gigas acts as pattern recognition receptor with broad recognition spectrum

The globular C1q domain containing (C1qDC) proteins are a family of versatile pattern recognition receptors (PRRs) to bind various ligands by their globular C1q (gC1q) domain. In the present study, a novel globular C1qDC (CgC1qDC-7) was characterized from Pacific oyster Crassostrea gigas. The open reading frame of CgC1qDC-7 was of 555 bp, encoding a polypeptide of 185 amino acids. Phylogenetic analysis indicated that CgC1qDC-7 shared high homology with C1qDCs from Crassostrea virginica, Mytilus galloprovincialis, and Mizuhopecten yessoensis. The mRNA transcripts of CgC1qDC-7 were widely expressed in all the tested tissues including mantle, gonad, gills, adductor muscle, hemocytes, hepatopancreas and labial palps, with the highest expression level in hemocytes and gills. The recombinant protein of CgC1qDC-7 (rCgC1qDC-7) exhibited binding activity towards Gram-negative bacteria (Vibrio splendidus, V. anguillarum, Escherichia coli, V. alginolyticus, and Aeromonas hydrophila), Gram-positive bacteria (Micrococcus luteus and Staphylococcus aureus) and fungi (Pichia pastoris and Yarrowia lipolytica), and displayed strongest binding affinity towards Gram-negative bacteria V. splendidus and V. anguillarum. It also exhibited affinity to vital pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharide (LPS), peptidoglycan (PGN), mannan (MAN) and Poly (I:C) with high affinity towards LPS and PGN, and low affinity to MAN and Poly (I:C). These results collectively indicated that CgC1qDC-7 was a novel PRR in C. gigas with high binding affinity towards LPS and PGN as well as Gram-negative bacteria.

Analysis of Anti-C1q Autoantibodies by Western Blot

Anti-C1q autoantibodies may be found in many conditions, most commonly in systemic lupus erythematosus (SLE) and hypocomplementemic urticarial vasculitis syndrome (HUVS), and are diagnostic markers as well as disease activity markers in lupus nephritis. Sera from patients with SLE and HUVS show partly distinct autoantibody reactivities to separated protein chains B and C of the first component of complement, C1q. These different binding specificities can be detected by Western blot analysis of the autoantibodies under reducing conditions. Results may help clinicians to differentiate between SLE and HUVS.

Modulation of Human Complement System by Antimicrobial Peptide Arenicin-1 from Arenicola marina

Antimicrobial peptides from marine invertebrates are known not only to act like cytotoxic agents, but they also can display some additional activities in mammalian organisms. In particular, these peptides can modulate the complement system as was described for tachyplesin, a peptide from the horseshoe crab. In this work, we investigated the influence on complement activation of the antimicrobial peptide arenicin-1 from the marine polychaete Arenicola marina. To study effects of arenicin on complement activation in human blood serum, we used hemolytic assays of two types, with antibody sensitized sheep erythrocytes and rabbit erythrocytes. Complement activation was also assessed, by the level of C3a production that was measured by ELISA. We found that the effect of arenicin depends on its concentration. At relatively low concentrations the peptide stimulates complement activation and lysis of target erythrocytes, whereas at higher concentrations arenicin acts as a complement inhibitor. A hypothetical mechanism of peptide action is proposed, suggesting its interaction with two complement proteins, C1q and C3. The results lead to the possibility of the development of new approaches for therapy of diseases connected with complement dysregulation, using peptide regulators derived from natural antimicrobial peptides of invertebrates.

The complement component 1 q (C1q) in Nile tilapia (Oreochromis niloticus): Functional characterization in host defense against bacterial infection and effect on cytokine response in macrophages

Complement component 1q (C1q) is the initial protein of the classical complement pathway and plays an important role in immune response against bacterial infection. In this study, the full-length of C1q subcomponent A, B and C chain genes (C1qA, C1qB and C1qC) were identified and characterized from Nile tilapia (Oreochromis niloticus). Molecular characterization of these three C1q subcomponents (OnC1qs) harbored conserved amino acids through analyses of multiple sequence alignment and phylogenetic tree, which were homologous to other teleost species. Expression analysis revealed that the OnC1qs were highly expressed in liver. After the in vivo challenges of Streptococcus agalactiae and LPS, the mRNA expressions of OnC1qs were significantly up-regulated in liver. Meanwhile, the concentration variation of OnC1qs at the protein level from tilapia serum after challenge with S. agalactiae were measured by a competitive-inhibition ELISA. In addition, the up-regulation expressions of OnC1qs were also demonstrated in head kidney adherent leukocytes and the cell culture medium in vitro stimulation with S. agalactiae, Aeromonas hydrophila and LPS, respectively. Moreover, the recombinant OnC1qs enhanced expression of cytokines IL-6, IL-8 and IL-10 in head kidney adherent leukocytes, and were able to bind both heat-aggregated mouse IgG and IgM. Taken together, the results of this study indicated that OnC1qs might be involved in host defense against bacterial infection in Nile tilapia.

C1q-Mediated Complement Activation and C3 Opsonization Trigger Recognition of Stealth Poly(2-methyl-2-oxazoline)-Coated Silica Nanoparticles by Human Phagocytes

Poly(2-methyl-2-oxazoline) (PMOXA) is an alternative promising polymer to poly(ethylene glycol) (PEG) for design and engineering of macrophage-evading nanoparticles (NPs). Although PMOXA-engineered NPs have shown comparable pharmacokinetics and in vivo performance to PEGylated stealth NPs in the murine model, its interaction with elements of the human innate immune system has not been studied. From a translational angle, we studied the interaction of fully characterized PMOXA-coated vinyltriethoxysilane-derived organically modified silica NPs (PMOXA-coated NPs) of approximately 100 nm in diameter with human complement system, blood leukocytes, and macrophages and compared their performance with PEGylated and uncoated NP counterparts. Through detailed immunological and proteomic profiling, we show that PMOXA-coated NPs extensively trigger complement activation in human sera exclusively through the classical pathway. Complement activation is initiated by the sensing molecule C1q, where C1q binds with high affinity ( K_d = 11 ± 1 nM) to NP surfaces independent of immunoglobulin binding. C1q-mediated complement activation accelerates PMOXA opsonization with the third complement protein (C3) through the amplification loop of the alternative pathway. This promoted NP recognition by human blood leukocytes and monocyte-derived macrophages. The macrophage capture of PMOXA-coated NPs correlates with sera donor variability in complement activation and opsonization but not with other major corona proteins, including clusterin and a wide range of apolipoproteins. In contrast to these observations, PMOXA-coated NPs poorly activated the murine complement system and were marginally recognized by mouse macrophages. These studies provide important insights into compatibility of engineered NPs with elements of the human innate immune system for translational steps.

C1q and Mannose-Binding Lectin Interact with CR1 in the Same Region on CCP24-25 Modules

Complement receptor type 1 (CR1) is a multi modular membrane receptor composed of 30 homologous complement control protein modules (CCP) organized in four different functional regions called long homologous repeats (LHR A, B, C, and D). CR1 is a receptor for complement-opsonins C3b and C4b and specifically interacts through pairs of CCP modules located in LHR A, B, and C. Defense collagens such as mannose-binding lectin (MBL), ficolin-2, and C1q also act as opsonins and are involved in immune clearance through binding to the LHR-D region of CR1. Our previous results using deletion variants of CR1 mapped the interaction site for MBL and ficolin-2 on CCP24-25. The present work aimed at deciphering the interaction of C1q with CR1 using new CR1 variants concentrated around CCP24-25. CR1 bimodular fragment CCP24-25 and CR1 CCP22-30 deleted from CCP24-25 produced in eukaryotic cells enabled to highlight that the interaction site for both MBL and C1q is located on the same pair of modules CCP24-25. C1q binding to CR1 shares with MBL a main common interaction site on the collagen stalks but also subsidiary sites most probably located on C1q globular heads, contrarily to MBL.

Cut-off values of immunological tests to identify patients at high risk of severe lupus nephritis

Cut-off values for anti-dsDNA, anti-nucleosome and anti-C1q antibodies tests and for complementmediated hemolytic activity (CH50) were explored to identify patients with high risk of developing severe lupus nephritis (LN). Forty-one patients with confirmed systemic lupus erythematosus (SLE) were identified; their levels for the three antibodies and complement had been measured on a same serum sample. These patients were classified based on the presence of renal involvem ent; sixteen had active proliferative LN. With the cut-off values accepted in the laboratory for SLE diagnosis (anti-dsDNA > 100 UI/ml, anti-nucleosome > 50 U/ml or CH50 < 190 UCH50%) no significant differences were found between patients with and without LN. Anti-C1q > 40 U/ml showed a statistically significant association with LN and had 80% of specificity. Cut-off values for LN identified by Receiver Operating Characteristic curves (ROC) were higher for anti-dsDNA (> 455 IU/ml) and antinucleosome (>107 U/ml), lower for CH50 (< 150 UCH50%) and, for anti-C1q (> 41 U/ml) coincided with the cut-off values accepted for SLE. Anti-C1q > 134 U/ml had a 92% of specificity, 56% of sensibility and was associated with a fifteen-fold increased risk of LN. The simultaneous presence of anti-nucleosome > 107 U/ml and anti-C1q > 134 U/ml was associated with a 27-fold higher probability for LN. According to these results, the cut-off values used to detect SLE activity could be inadequate to identify patients at high risk of severe LN.

IgG Endopeptidase in Highly Sensitized Patients Undergoing Transplantation

BACKGROUND

Donor-specific antibodies create an immunologic barrier to transplantation. Current therapies to modify donor-specific antibodies are limited and ineffective in the most highly HLA-sensitized patients. The IgG-degrading enzyme derived from Streptococcus pyogenes (IdeS), an endopeptidase, cleaves human IgG into F(ab')₂ and Fc fragments inhibiting complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity, which suggests that IdeS might be useful for desensitization. We report on the combined experience of two independently performed open-label, phase 1-2 trials (conducted in Sweden and the United States) that assessed the efficacy of IdeS with regard to desensitization and transplantation of a kidney from an HLA-incompatible donor.

METHODS

We administered IdeS to 25 highly HLA-sensitized patients (11 patients in Uppsala or Stockholm, Sweden, and 14 in Los Angeles) before the transplantation of a kidney from an HLA-incompatible donor. Frequent monitoring for adverse events, outcomes, donor-specific antibodies, and renal function was performed, as were renal biopsies. Immunosuppression after transplantation consisted of tacrolimus, mycophenolate mofetil, and glucocorticoids. Patients in the U.S. study also received intravenous immune globulin and rituximab after transplantation to prevent antibody rebound.

RESULTS

Recipients in the U.S. study had a significantly longer cold ischemia time (the time elapsed between procurement of the organ and transplantation), a significantly higher rate of delayed graft function, and significantly higher levels of class I donor-specific antibodies than those in the Swedish study. A total of 38 serious adverse events occurred in 15 patients (5 events were adjudicated as being possibly related to IdeS). At transplantation, total IgG and HLA antibodies were eliminated. A total of 24 of 25 patients had perfusion of allografts after transplantation. Antibody-mediated rejection occurred in 10 patients (7 patients in the U.S. study and 3 in the Swedish study) at 2 weeks to 5 months after transplantation; all these patients had a response to treatment. One graft loss, mediated by non-HLA IgM and IgA antibodies, occurred.

CONCLUSIONS

IdeS reduced or eliminated donor-specific antibodies and permitted HLA-incompatible transplantation in 24 of 25 patients. (Funded by Hansa Medical; ClinicalTrials.gov numbers, NCT02224820 , NCT02426684 , and NCT02475551 .).

Renal manifestations in hypocomplementic urticarial vasculitis syndrome: Is it a distinct pathology?

Hypocomplementic urticarial vasculitis syndrome (HUVS) is an autoimmune disease characterized by recurrent urticaria, arthritis, and glomerulonephritis (GN). Anti-C1q antibody is the marker of HUVS together with low levels of classical pathway complements which are C2, C3, C4, and C1q. We report a case of a 6-year-old boy who presented with episodes of rashes, injected conjunctiva, abdominal pain, and arthritis, diagnosed as HUVS. He had low C3, low CH50, normal C4, and positive C1q antibody. His urinalysis showed intermittent microscopic hematuria only. One year later, his laboratories showed persistent low C3 and positive Anti-ds DNA. The urinalysis showed hematuria, pyuria, and nephrotic-range proteinuria. Urine protein to creatinine ratio was 101.8 h mg/mmol. Kidney biopsy showed mesangioproliferative GN consistent with the diagnosis of HUVS. The patient was treated initially with prednisolone then azathioprine was added to the regimen. He showed good response with the disappearance of hematuria and proteinuria. Nine months later, he had no skin rashes with normal urinalysis and normal anti-ds DNA antibody. We report a case with HUVS and GN with positive anti-dsDNA antibody that revealed good response to combination of immunosuppressive therapy.

Improvement in the definition of anti-HLA antibody profile in highly sensitized patients

The definition of anti-HLA antibody profile in highly sensitized patients on a waiting list is crucial when virtual crossmatch is used in organ allocation systems, but also when used to identify the true deleterious anti-HLA antibodies. Here we propose different levels of risk based on the results of anti-HLA antibody testing in neat serum (N) and after sera dilution (DIL) and C1q test in 18 highly sensitized patients. This group was heterogeneous in terms of anti-HLA antibody titers and their ability to fix complement. After dilution, 15 out of 18 patients (83.3%) showed a reduction of positive bead counts whereas 4 patients showed a prozone effect and complement fixation was demonstrated. The high dilution of sera and ascertaining the complement fixation allow the accurate definition of risk anti-HLA antibody profiles in highly sensitized patients, as demonstrated in 5 of the sensitized patients who were transplanted.

The Spectrum of Renal Allograft Failure

Background

Causes of “true” late kidney allograft failure remain unclear as study selection bias and limited follow-up risk incomplete representation of the spectrum.

Methods

We evaluated all unselected graft failures from 2008–2014 (n = 171; 0–36 years post-transplantation) by contemporary classification of indication biopsies “proximate” to failure, DSA assessment, clinical and biochemical data.

Results

The spectrum of graft failure changed markedly depending on the timing of allograft failure. Failures within the first year were most commonly attributed to technical failure, acute rejection (with T-cell mediated rejection [TCMR] dominating antibody-mediated rejection [ABMR]). Failures beyond a year were increasingly dominated by ABMR and ‘interstitial fibrosis with tubular atrophy’ without rejection, infection or recurrent disease (“IFTA”). Cases of IFTA associated with inflammation in non-scarred areas (compared with no inflammation or inflammation solely within scarred regions) were more commonly associated with episodes of prior rejection, late rejection and nonadherence, pointing to an alloimmune aetiology. Nonadherence and late rejection were common in ABMR and TCMR, particularly Acute Active ABMR. Acute Active ABMR and nonadherence were associated with younger age, faster functional decline, and less hyalinosis on biopsy. Chronic and Chronic Active ABMR were more commonly associated with Class II DSA. C1q-binding DSA, detected in 33% of ABMR episodes, were associated with shorter time to graft failure. Most non-biopsied patients were DSA-negative (16/21; 76.1%). Finally, twelve losses to recurrent disease were seen (16%).

Conclusion

This data from an unselected population identifies IFTA alongside ABMR as a very important cause of true late graft failure, with nonadherence-associated TCMR as a phenomenon in some patients. It highlights clinical and immunological characteristics of ABMR subgroups, and should inform clinical practice and individualised patient care.

Association of C1q Binding Status With De Novo HLA Antibody Clinical Features and Allograft Function in Kidney Transplantation Patients During Eight Years of Dynamic Follow-up

BACKGROUND

C1q-binding donor-specific antibody (DSA) is detrimental to transplanted kidney function. However, the factors that affect C1q binding status are unclear.

METHODS

A total of 519 samples from 129 consecutive kidney transplantation patients during 8 years of dynamic follow-up were collected for HLA antibody (Ab) screening and C1q detection.

RESULTS

Among the detected HLA Abs, the majority were class II, and the DQ subtypes composed the highest proportion. The C1q-binding Abs were all HLA-II, and the DQ subtypes had the highest rate of C1q positivity. With a cutoff mean fluorescence intensity (MFI) value of 7349, the sensitivity and specificity of detecting C1q-binding Abs from all HLA-II Abs were 84.48% and 83.56%, respectively. Additionally, C1q is more likely to be bound by DSA than non-donor-specific antibody (NDSA). Compared with free DSA/NDSA, the MFI values of C1q-binding DSA/NDSA are more closely correlated with serum creatinine levels and reflect the effect of anti-antibody-mediated rejection treatment more sensitively.

CONCLUSIONS

HLA-II Abs (particularly DQ subtypes), high titers of Abs, and DSA are important relevant factors of C1q positivity. The MFI value of C1q-binding DSA may be a useful clinical indicator of HLA antibody-mediated graft injury before the appearance of histologically typical humoral rejection.

Interpreting Anti-HLA Antibody Testing Data: A Practical Guide for Physicians

The development of sensitive methods for alloantibody detection has been a significant advance in clinical transplantation. However, the complexity of the data from solid phase and crossmatch assays has led to potential confusion about how to use the results for clinical decision making. The goal of this review is to provide a practical guide for transplant physicians for the interpretation of antibody data to supplement consultation with local tissue typing experts. Sources of variability in both the solid phase and crossmatch assay are discussed as are recent data regarding C1q binding antibodies and IgG subclass testing. Although definitive approaches to alloantibody testing are not possible with our current knowledge, we outline a pragmatic approach that we hope will enhance clinical management in this area.

Further description of early clinically silent lupus nephritis

Thirty silent lupus nephritis (SLN) patients were compared to 16 individuals bearing overt lupus nephritis (OLN). Results included: years of systemic lupus erythematosus (SLE) diagnosis were significantly earlier (4.6 ± 2.8 years) in SLN than in OLN (7.18 ± 3.61) ( P < 0.05). Neurological compromise, hypertension, normocitic anemia and lymphopenia were significantly prevalent in OLN than in SLN ( P < 0.05). Beside normal urinary sediment and renal function tests, the SLN group showed a moderate increase of both activity (AI) and chronicity (CI) renal pathology index when compared to highly increased AI and CI in OLN ( P < 0.05). Seventy percent of SLN patients were ISN/RPS Classes I (6.6%) and II (63.3%) while 81% of OLN cases were Classes III, IV (37.5%) and V. IgG, IgA, IgM, λchain, C3 and fibrinogen immune deposits were found in 90% or over in both SLN and OLN individuals while in 60% or over, both groups also showed K chain, C1q and C4 deposits. While prevalence of ANA, anti-dsDNA and anti-C1q antibodies were similar in both groups, anti-histone, anti-RNP, CIC and CH50 serum levels were significantly different in OLN versus SLN ( P < 0.05). We strongly suggest that indeed SLN is the earliest stage in the natural history of lupus nephritis.

Molecular Basis of Assembly and Activation of Complement Component C1 in Complex with Immunoglobulin G1 and Antigen

The classical complement pathway contributes to the natural immune defense against pathogens and tumors. IgG antibodies can assemble at the cell surface into hexamers via Fc:Fc interactions, which recruit complement component C1q and induce complement activation. Biophysical characterization of the C1:IgG complex has remained elusive primarily due to the low affinity of IgG-C1q binding. Using IgG variants that dynamically form hexamers efficient in C1q binding and complement activation, we could assess C1q binding in solution by native mass spectrometry and size-exclusion chromatography. Fc-domain deglycosylation, described to abrogate complement activation, affected IgG hexamerization and C1q binding. Strikingly, antigen binding by IgG hexamers or deletion of the Fab arms substantially potentiated complement initiation, suggesting that Fab-mediated effects impact downstream Fc-mediated events. Finally, we characterized a reconstituted 2,045.3 ± 0.4-kDa complex of intact C1 bound to antigen-saturated IgG hexamer by native mass spectrometry, providing a clear visualization of a complete complement initiation complex.

Complement and microglia mediate early synapse loss in Alzheimer mouse models

Synapse loss in Alzheimer's disease (AD) correlates with cognitive decline. Involvement of microglia and complement in AD has been attributed to neuroinflammation, prominent late in disease. Here we show in mouse models that complement and microglia mediate synaptic loss early in AD. C1q, the initiating protein of the classical complement cascade, is increased and associated with synapses before overt plaque deposition. Inhibition of C1q, C3, or the microglial complement receptor CR3 reduces the number of phagocytic microglia, as well as the extent of early synapse loss. C1q is necessary for the toxic effects of soluble β-amyloid (Aβ) oligomers on synapses and hippocampal long-term potentiation. Finally, microglia in adult brains engulf synaptic material in a CR3-dependent process when exposed to soluble Aβ oligomers. Together, these findings suggest that the complement-dependent pathway and microglia that prune excess synapses in development are inappropriately activated and mediate synapse loss in AD.

Amblyomma americanum tick calreticulin binds C1q but does not inhibit activation of the classical complement cascade

In this study we characterized Amblyomma americanum (Aam) tick calreticulin (CRT) homolog in tick feeding physiology. In nature, different tick species can be found feeding on the same animal host. This suggests that different tick species found feeding on the same host can modulate the same host anti-tick defense pathways to successfully feed. From this perspective it's plausible that different tick species can utilize universally conserved proteins such as CRT to regulate and facilitate feeding. CRT is a multi-functional protein found in most taxa that is injected into the vertebrate host during tick feeding. Apart from it's current use as a biomarker for human tick bites, role(s) of this protein in tick feeding physiology have not been elucidated. Here we show that annotated functional CRT amino acid motifs are well conserved in tick CRT. However our data show that despite high amino acid identity levels to functionally characterized CRT homologs in other organisms, AamCRT is apparently functionally different. Pichia pastoris expressed recombinant (r) AamCRT bound C1q, the first component of the classical complement system, but it did not inhibit activation of this pathway. This contrast with reports of other parasite CRT that inhibited activation of the classical complement pathway through sequestration of C1q. Furthermore rAamCRT did not bind factor Xa in contrast to reports of parasite CRT binding factor Xa, an important protease in the blood clotting system. Consistent with this observation, rAamCRT did not affect plasma clotting or platelet aggregation. We discuss our findings in the context of tick feeding physiology.

Apoptosis signal-regulating kinase 1 mediates striatal degeneration via the regulation of C1q

Apoptosis signal-regulating kinase-1 (ASK1), an early signaling element in the cell death pathway, has been hypothesized to participate in the pathology of neurodegenerative diseases. The systemic administration of 3-nitropropionic acid (3-NP) facilitates the development of selective striatal lesions. However, it remains unclear whether specific neurons are selectively targeted in 3-NP-infused striatal degeneration. Recently, it has been proposed that complement-mediated synapse elimination may be reactivated aberrantly in the pathology of neurodegenerative diseases. We hypothesized that ASK1 is involved in striatal astrocyte reactivation; reactive astrocyte secretes molecules detrimental to neuron; and striatal neurons are more susceptible to these factors. Our results indicate that striatal astrocyte is reactivated and ASK1 level increases after 3-NP general and chronic infusion. Reactive striatal astrocyte increases TGF-beta differentially to cortex and striatum. ASK1 may be involved in regulation of astrocyte TGF-beta and it is linked to the C1q level in spatial and temporal, and moreover in the earlier stage of progressing striatal neuronal loss. Conclusively the present study suggests that ASK1 mediates 3-NP toxicity and regulates C1q level through the astrocyte TGF-beta. And also it may suggest that C1q level may be a surrogate of prediction marker representing neurodegenerative disease progress before developing behavioral impairment.

L-C1qDC-1, a novel C1q domain-containing protein from Lethenteron camtschaticum that is involved in the immune response

The C1q domain-containing (C1qDC) proteins are a family of proteins characterized by a globular C1q (gC1q) domain at their C-terminus. These proteins are involved in various processes in vertebrates and are assumed to serve as important pattern recognition receptors in innate immunity in invertebrates. Here, a novel C1qDC protein from Lethenteron camtschaticum was identified and characterized (designated as L-C1qDC-1). After a partial cDNA sequence of L-C1qDC-1 was identified in a L. camtschaticum liver cDNA library, the full-length cDNA was obtained using 3'- and 5'-rapid amplification of cDNA ends (RACE). L-C1qDC-1 encodes 236 amino acids and contains a signal peptide, a collagen-like sequence with Gly-Xaa-Yaa repeats, and a C-terminal gC1q domain. The L-C1qDC-1 protein was primarily distributed in the gut, liver and supraneural body of L. camtschaticum and was also marginally detectable in leukocytes via real-time PCR and immunofluorescence assays. Furthermore, both immunoprecipitation and immunofluorescence results showed that in L. camtschaticum serum, L-C1qDC-1 could interact with variable lymphocyte receptor (VLR) B and displayed strong colocalization with cancer cell immune responses. These results indicated that the L-C1qDC-1 gene encodes a novel C1qDC protein that may play an important role in the immune responses of L. camtschaticum, providing clues for understanding the universal functions of C1qDC proteins in other species and suggesting that these proteins could serve as pattern recognition molecules in immunotherapy.

Correlation of Circulating Complement-Fixing Donor-Specific Antibodies Identified by the C1q Assay and Presence of C4d in Endomyocardial Biopsy Specimens

OBJECTIVES

Donor-specific antibodies (DSAs) are associated with increased cardiac graft loss. We applied a C1q solid-phase assay in parallel with the standard immunoglobulin G (IgG) single antigen bead (SAB) assay to examine the correlation of circulating complement-fixing donor-specific antibodies and the presence of C4d in endomyocardial biopsy (EMB) specimens.

METHODS

We retrospectively studied the relationship of C1q+ DSAs and C4d immunofluorescence (IF) in 49 EMB specimens from 44 heart transplant recipients who had concurrent EMB, C4d IF, and DSA measurements. We applied a C1q SAB in parallel with the standard IgG SAB assay to examine the DSA profiles in heart transplant patients posttransplant.

RESULTS

A better concordance is observed between C1q+ DSAs with C4d IF+ compared with IgG DSAs with C4d IF + (40% vs 24%, P = .02). However, the correlation of C1q DSAs with C4d IF is not statistically significant (P = .24). Importantly, C1q+ DSAs were observed in 16 of 17 cases with C4d IF+; 24 cases had circulating C1q+ DSAs without detectable C4d staining, suggesting that that the presence of C1q+ DSAs may precede the detection of C4d deposition in EMB specimens and/or the development of antibody-mediated rejection.

CONCLUSIONS

In this cohort of 44 patients, no significant correlation was observed between circulating C1q DSAs and C4d IF in EMB specimens. Additional studies are needed to further evaluate the association of C1q DSAs with EMB specimens and C4d staining.

Innate immune humoral factors, C1q and factor H, with differential pattern recognition properties, alter macrophage response to carbon nanotubes

Interaction between the complement system and carbon nanotubes (CNTs) can modify their intended biomedical applications. Pristine and derivatised CNTs can activate complement primarily via the classical pathway which enhances uptake of CNTs and suppresses pro-inflammatory response by immune cells. Here, we report that the interaction of C1q, the classical pathway recognition molecule, with CNTs involves charge pattern and classical pathway activation that is partly inhibited by factor H, a complement regulator. C1q and its globular modules, but not factor H, enhanced uptake of CNTs by macrophages and modulated the pro-inflammatory immune response. Thus, soluble complement factors can interact differentially with CNTs and alter the immune response even without complement activation. Coating CNTs with recombinant C1q globular heads offers a novel way of controlling classical pathway activation in nanotherapeutics. Surprisingly, the globular heads also enhance clearance by phagocytes and down-regulate inflammation, suggesting unexpected complexity in receptor interaction.

FROM THE CLINICAL EDITOR

Carbon nanotubes (CNTs) maybe useful in the clinical setting as targeting drug carriers. However, it is also well known that they can interact and activate the complement system, which may have a negative impact on the applicability of CNTs. In this study, the authors functionalized multi-walled CNT (MWNT), and investigated the interaction with the complement pathway. These studies are important so as to gain further understanding of the underlying mechanism in preparation for future use of CNTs in the clinical setting.

Antibodies against C1q Are a Valuable Serological Marker for Identification of Systemic Lupus Erythematosus Patients with Active Lupus Nephritis

OBJECTIVE

An early diagnosis of lupus nephritis (LN) has an important clinical implication in guiding treatments of systemic lupus erythematosus (SLE) in clinical settings. In this study, the diagnostic values of circulating autoantibodies to C1q alone or in combination with other markers for accessing active SLE and LN were evaluated.

METHODS

The diagnostic value of anti-C1q autoantibodies for identification of patients with active SLE disease and LN was evaluated by analyzing the level of anti-C1q antibodies in sera from 95 SLE patients, 40 non-SLE patients, and 34 healthy cohorts.

RESULTS

The prevalence of anti-C1q antibodies was significantly higher in patients with SLE (50/95, 52.6%), active SLE (40/51, 78.4%), and LN (30/35, 85.7%) in comparison with non-SLE patient controls, patients with inactive SLE, and non-LN, respectively. A combination of anti-C1q with anti-dsDNA and/or levels of complements C3 and C4 exhibited an increased specificity but a decreased sensitivity for identification of patients with active SLE and LN diseases relative to each of these markers alone.

CONCLUSION

Anti-C1q antibodies were strongly associated with disease activity and LN in SLE patients, suggesting that it may be a reliable serological marker for identification of SLE patients with active LN and active SLE disease.

Sialylation of IgG Fc domain impairs complement-dependent cytotoxicity

IgG molecules exert both pro- and antiinflammatory effector functions based on the composition of the fragment crystallizable (Fc) domain glycan. Sialylated IgG Fc domains have antiinflammatory properties that are attributed to their ability to increase the activation threshold of innate effector cells to immune complexes by stimulating the upregulation of the inhibitory Fcγ receptor IIB (FcγRIIB). Here, we report that IgG Fc sialylation of human monoclonal IgG1 molecules impairs their efficacy to induce complement-mediated cytotoxicity (CDC). Fc sialylation of a CD20-targeting antibody had no impact on antibody-dependent cellular cytotoxicity and did not change the affinity of the antibody for activating Fcγ receptors. In contrast, the presence of sialic acid abrogated the increased binding of C1q to Fc-galactosylated IgG1 and resulted in decreased levels of C3b deposition on the cell surface. Similar to monoclonal antibodies, sialic acid inhibited the increased C1q binding to galactosylated Fc fragments in human polyclonal IgG. In sera derived from patients with chronic inflammatory demyelinating polyneuropathy, an autoimmune disease of the peripheral nervous system in which humoral immune responses mediate tissue damage, induction of IgG Fc sialylation was associated with clinical disease remission. Thus, impairment of CDC represents an FcγR-independent mechanism by which Fc-sialylated glycovariants might limit proinflammatory IgG effector functions.

[C1Q NEPHROPATHY: CASE REPORTS AND LITERATURE REVIEW]

C1q nephropathy is considered a form of glomerulonephritis, defined by histological findings of dominant Clq immune deposits in renal biopsy. It is a rare disease, most often manifested in children and young adults. The most common clinical manifestation of the disease is nephrotic syndrome, but other renal syndromes could also be found. The cause of the disease is not known, but the immune pathogenesis could be assumed. Often, resistance to glucocorticoid or other immunosuppressive therapy is present, potentially leading to chronic renal insufficiency. We present ten patients with renal biopsy and clinical findings of Clq nephropathy. None of the patients had clinical or serological manifestations of systemic lupus. All patients had normal findings of C3 and C4 components of complement, as well as normal ANF, anti-dsD-NA and ANCA antibodies.