New Insights into Molecular Mechanisms of Immune Complex-Induced Injury in Lung

Are Changes in Serum IgG Glycosylation Related to the Severe Course of SARS-CoV-2 Infection and Recovery Process? In Search of New Diagnostic and Prognostic Biomarkers

Introduction

Immunoglobulin G (IgG) glycosylation affects its effector functions and is essential in many steps of the inflammatory cascade. Therefore, it may be an important parameter for assessing the body's immune response during the course of COVID-19 (Coronavirus disease 2019).

Methods

The N- and O-glycosylation of serum IgG in severe COVID-19 patients (n=87), convalescents (n=50), and healthy subjects (n=65) were examined using a modified lectin-ELISA method with specific biotinylated lectins. The obtained data were analyzed using STATISTICA 13.3PL software.

Results

We showed significantly higher expression of Lewisx oligosaccharide structures in severe COVID-19 patients than in the other two groups. Moreover, significantly lower expression of Lewisy sugar structures in IgG glycans was observed in the convalescents when compared with COVID-19 patients and healthy subjects. The lowest expression of highly branched N-glycans in cases of severe COVID-19 indicates that the development of the disease is associated with the presence of typical IgG biantennary N-glycans. The lack of significant differences in the expression of Tn antigen in IgG between studied groups and the significantly lower expression of T antigen in convalescents compared to the patients with severe COVID-19 and healthy subjects indicates a decrease in the content of the T antigen in IgG O-glycans in subjects recovered from COVID-19. Substantially higher reactivities of IgG O-glycans with Jacalin observed in COVID-19 patients and convalescents in comparison to the control group were most probably caused by increased expression of core 3 O-glycans in IgG.

Conclusion

Severe COVID-19 is accompanied by the expression in serum IgG of sialylated biantennary and highly branched N-glycans, decorated by fucose of Lewisx and Lewisy structures. The higher reactivity of IgG O-glycans with Jacalin in severe COVID-19 patients and convalescents indicates that the disease development and the recovery process are most probably accompanied by increased expression of the core 3 O-glycans.

Immunosenescence and Inflammaging in COVID-19

Despite knowledge gaps in understanding the full spectrum of the hyperinflammatory phase caused by SARS-CoV-2, according to the World Health Organization (WHO), COVID-19 is still the leading cause of death worldwide. Susceptible people to severe COVID-19 are those with underlying medical conditions or those with dysregulated and senescence-associated immune responses. As the immune system undergoes aging in the elderly, such drastic changes predispose them to various diseases and affect their responsiveness to infections, as seen in COVID-19. At-risk groups experience poor prognosis in terms of disease recovery. Changes in the quantity and quality of immune cell function have been described in numerous literature sites. Impaired immune cell function along with age-related metabolic changes can lead to features such as hyperinflammatory response, immunosenescence, and inflammaging in COVID-19. Inflammaging is related to the increased activity of the most inflammatory factors and is the main cause of age-related diseases and tissue failure in the elderly. Since hyperinflammation is a common feature of most severe cases of COVID-19, this pathway, which is not fully understood, leads to immunosenescence and inflammaging in some individuals, especially in the elderly and those with comorbidities. In this review, we shed some light on the age-related abnormalities of innate and adaptive immune cells and how hyperinflammatory immune responses contribute to the inflammaging process, leading to clinical deterioration. Further, we provide insights into immunomodulation-based therapeutic approaches, which are potentially important considerations in vaccine design for elderly populations.

IgG immune complex-induced acute lung injury is ameliorated by cAMP via down-regulation of C/EBP- and AP-1-mediated transcriptions

BACKGROUND

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS) are life threatening pulmonary diseases, and we are now lack of effective therapeutic methods. Inflammatory responses are essential for initiating ALI/ARDS. Thus, ameliorating inflammatory reaction might be beneficial for treatment of the disease. There are increasing data that phosphodiesterase-4 (PDE4)-selective inhibitors, which may elevate cellular cyclic adenosine 3', 5'-monophosphate (cAMP) level, could suppress inflammation. However, whether they could be used to treat IgG immune complex (IgG-IC)-associated ALI has not been determined.

METHODS

ALI is induced by treating mice with airway deposition of IgG immune complexes. Cellular cAMP concentrations are elevated by treating mice or macrophages with Rolipram/Roflumilast. The degree of pulmonary injury is reflected by lung permeability, leukocyte accumulation, histological change and expressions of pro-inflammatory mediators. 6-Bnz-cAMP and H-89 are used to regulate protein kinase A (PKA) activity, and 8-pCPT-2'-O-Me-cAMP is applied to activate exchange proteins directly activated by cAMP (Epac). Gene expressions are analyzed by real-time PCR, ELISA or Western blot. CCAAT/enhancer binding protein (C/EBP) and activation protein 1 (AP-1) transcription activities are estimated by measuring the luciferase productions.

RESULTS

IgG-IC-induced ALI is attenuated by the PDE4-selective inhibitor, which is due to reduced expressions of cytokine and chemokines. Interestingly, we find that cAMP downstream effector molecule PKA but not Epac is involved in negative regulation of IgG-IC-mediated pro-inflammatory mediators' productions. Mechanistically, activation of cAMP-PKA signal axis leads to inactivation of MAPK pathway, resulting in a decrease in C/EBP- and AP-1-mediated transcriptions of pro-inflammatory mediators.

CONCLUSIONS

Our data demonstrate, for the first time, that cAMP-PKA signal is involved in down-regulation of IgG-IC-associated inflammatory responses via down-regulating MAPK activation, which is critical for transcriptional activities of C/EBP and AP-1. Collectively, our experiments provide theoretical base for the potential application of PDE4-selective inhibitor to clinic for treatment of IgG-IC-related acute lung injury.

Invariant natural killer T cells in lung diseases

Invariant natural killer T (iNKT) cells are a subset of T cells that are characterized by a restricted T-cell receptor (TCR) repertoire and a unique ability to recognize glycolipid antigens. These cells are found in all tissues, and evidence to date suggests that they play many immunological roles in both homeostasis and inflammatory conditions. The latter include lung inflammatory diseases such as asthma and infections: the roles of lung-resident iNKT cells in these diseases have been extensively researched. Here, we provide insights into the biology of iNKT cells in health and disease, with a particular focus on the role of pulmonary iNKT cells in airway inflammation and other lung diseases.

Immunopathology of terminal complement activation and complement C5 blockade creating a pro-survival and organ-protective phenotype in trauma

BACKGROUND AND PURPOSE

Traumatic haemorrhage (TH) is the leading cause of potentially preventable deaths that occur during the prehospital phase of care. No effective pharmacological therapeutics are available for critical TH patients yet. Here, we identify terminal complement activation (TCA) as a therapeutic target in combat casualties and evaluate the efficacy of a TCA inhibitor (nomacopan) on organ damage and survival in vivo.

EXPERIMENTAL APPROACH

Complement activation products and cytokines were analysed in plasma from 54 combat casualties. The correlations between activated complement pathway(s) and the clinical outcomes in trauma patients were assessed. Nomacopan was administered to rats subjected to lethal TH (blast injury and haemorrhagic shock). Effects of nomacopan on TH were determined using survival rate, organ damage, physiological parameters, and laboratory profiles.

KEY RESULTS

Early TCA was associated with systemic inflammatory responses and clinical outcomes in this trauma cohort. Lethal TH in the untreated rats induced early TCA that correlated with the severity of tissue damage and mortality. The addition of nomacopan to a damage-control resuscitation (DCR) protocol significantly inhibited TCA, decreased local and systemic inflammatory responses, improved haemodynamics and metabolism, attenuated tissue and organ damage, and increased survival.

CONCLUSION AND IMPLICATIONS

Previous findings of our and other groups revealed that early TCA represents a rational therapeutic target for trauma patients. Nomacopan as a pro-survival and organ-protective drug, could emerge as a promising adjunct to DCR that may significantly reduce the morbidity and mortality in severe TH patients while awaiting transport to critical care facilities.

Xuanfei Baidu Decoction suppresses complement overactivation and ameliorates IgG immune complex-induced acute lung injury by inhibiting JAK2/STAT3/SOCS3 and NF-κB signaling pathway

BACKGROUND

The significant clinical efficacy of Xuanfei Baidu Decoction (XFBD) is proven in the treatment of patients with coronavirus disease 2019 (COVID-19) in China. However, the mechanisms of XFBD against acute lung injury (ALI) are still poorly understood.

METHODS

In vivo, the mouse model of ALI was induced by IgG immune complexes (IgG-IC), and then XFBD (4g/kg, 8g/kg) were administered by gavage respectively. 24 h after inducing ALI, the lungs were collected for histological and molecular analysis. In vitro, alveolar macrophages inflammation models induced by IgG-IC were performed and treated with different dosage of XFBD-containing serum to investigate the protective role and molecular mechanisms of XFBD.

RESULTS

The results revealed that XFBD mitigated lung injury and significantly downregulated the production of pro-inflammatory mediators in lung tissues and macrophages upon IgG-IC stimulation. Notably, XFBD attenuated C3a and C5a generation, inhibited the expression of C3aR and C5aR and suppressed the activation of JAK2/STAT3/SOCS3 and NF-κB signaling pathway in lung tissues and macrophages induced by IgG-IC. Moreover, in vitro experiments, we verified that Colivelin TFA (CAF, STAT3 activator) and C5a treatment markedly elevated the IgG-IC-triggered inflammatory responses in macrophages and XFBD weakened the effects of CAF or C5a.

CONCLUSION

XFBD suppressed complement overactivation and ameliorated IgG immune complex-induced acute lung injury by inhibiting JAK2/STAT3/SOCS3 and NF-κB signaling pathway. These data contribute to understanding the mechanisms of XFBD in COVID-19 treatment.

From acute SARS-CoV-2 infection to pulmonary hypertension

As the world progressively recovers from the acute stages of the coronavirus disease 2019 (COVID-19) pandemic, we may be facing new challenges regarding the long-term consequences of COVID-19. Accumulating evidence suggests that pulmonary vascular thickening may be specifically associated with COVID-19, implying a potential tropism of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) virus for the pulmonary vasculature. Genetic alterations that may influence the severity of COVID-19 are similar to genetic drivers of pulmonary arterial hypertension. The pathobiology of the COVID-19-induced pulmonary vasculopathy shares many features (such as medial hypertrophy and smooth muscle cell proliferation) with that of pulmonary arterial hypertension. In addition, the presence of microthrombi in the lung vessels of individuals with COVID-19 during the acute phase, may predispose these subjects to the development of chronic thromboembolic pulmonary hypertension. These similarities raise the intriguing question of whether pulmonary hypertension (PH) may be a long-term sequela of SARS-COV-2 infection. Accumulating evidence indeed support the notion that SARS-COV-2 infection is indeed a risk factor for persistent pulmonary vascular defects and subsequent PH development, and this could become a major public health issue in the future given the large number of individuals infected by SARS-COV-2 worldwide. Long-term studies assessing the risk of developing chronic pulmonary vascular lesions following COVID-19 infection is of great interest for both basic and clinical research and may inform on the best long-term management of survivors.

Early non-neutralizing, afucosylated antibody responses are associated with COVID-19 severity

A damaging inflammatory response is implicated in the pathogenesis of severe coronavirus disease 2019 (COVID-19), but mechanisms contributing to this response are unclear. In two prospective cohorts, early non-neutralizing, afucosylated immunoglobulin G (IgG) antibodies specific to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were associated with progression from mild to more severe COVID-19. To study the biology of afucosylated IgG immune complexes, we developed an in vivo model that revealed that human IgG-Fc-gamma receptor (FcγR) interactions could regulate inflammation in the lung. Afucosylated IgG immune complexes isolated from patients with COVID-19 induced inflammatory cytokine production and robust infiltration of the lung by immune cells. In contrast to the antibody structures that were associated with disease progression, antibodies that were elicited by messenger RNA SARS-CoV-2 vaccines were highly fucosylated and enriched in sialylation, both modifications that reduce the inflammatory potential of IgG. Vaccine-elicited IgG did not promote an inflammatory lung response. These results show that human IgG-FcγR interactions regulate inflammation in the lung and define distinct lung activities mediated by the IgG that are associated with protection against, or progression to, severe COVID-19.

Detection and functional resolution of soluble immune complexes by an FcγR reporter cell panel

Fc-gamma receptor (FcγR) activation by soluble IgG immune complexes (sICs) represents a major mechanism of inflammation in certain autoimmune diseases such as systemic lupus erythematosus (SLE). A robust and scalable test system allowing for the detection and quantification of sIC bioactivity is missing. We developed a comprehensive reporter cell panel detecting activation of FcγRs. The reporter cell lines were integrated into an assay that enables the quantification of sIC reactivity via ELISA or a faster detection using flow cytometry. This identified FcγRIIA(H) and FcγRIIIA as the most sIC-sensitive FcγRs in our test system. Reaching a detection limit in the very low nanomolar range, the assay proved also to be sensitive to sIC stoichiometry and size reproducing for the first time a complete Heidelberger-Kendall curve in terms of immune receptor activation. Analyzing sera from SLE patients and mouse models of lupus and arthritis proved that sIC-dependent FcγR activation has predictive capabilities regarding severity of SLE disease. The assay provides a sensitive and scalable tool to evaluate the size, amount, and bioactivity of sICs in all settings.

Potential long-term effects of SARS-CoV-2 infection on the pulmonary vasculature: a global perspective

The lungs are the primary target of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, with severe hypoxia being the cause of death in the most critical cases. Coronavirus disease 2019 (COVID-19) is extremely heterogeneous in terms of severity, clinical phenotype and, importantly, global distribution. Although the majority of affected patients recover from the acute infection, many continue to suffer from late sequelae affecting various organs, including the lungs. The role of the pulmonary vascular system during the acute and chronic stages of COVID-19 has not been adequately studied. A thorough understanding of the origins and dynamic behaviour of the SARS-CoV-2 virus and the potential causes of heterogeneity in COVID-19 is essential for anticipating and treating the disease, in both the acute and the chronic stages, including the development of chronic pulmonary hypertension. Both COVID-19 and chronic pulmonary hypertension have assumed global dimensions, with potential complex interactions. In this Review, we present an update on the origins and behaviour of the SARS-CoV-2 virus and discuss the potential causes of the heterogeneity of COVID-19. In addition, we summarize the pathobiology of COVID-19, with an emphasis on the role of the pulmonary vasculature, both in the acute stage and in terms of the potential for developing chronic pulmonary hypertension. We hope that the information presented in this Review will help in the development of strategies for the prevention and treatment of the continuing COVID-19 pandemic.

In this Review, the authors discuss the potential causes of the heterogeneity of COVID-19 and summarize the pathobiology of the disease, with an emphasis on the role of the pulmonary vasculature in the acute stage and the potential for developing chronic pulmonary hypertension.

A thorough understanding of the dynamic behaviour of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential to understanding its heterogeneous effects on the pulmonary vasculature in patients with coronavirus disease 2019 (COVID-19).

The severity and clinical phenotype of COVID-19 are influenced by host factors, including socioeconomic factors and genetics.

Silent hypoxia is a major and independent cause of lung damage in COVID-19; the use of modern imaging techniques is proving to be very valuable in identifying silent hypoxia.

The pulmonary vascular system has a major role in the pathobiology of COVID-19.

Both COVID-19 and chronic pulmonary hypertension are global diseases with a complex interaction.

Is It All About Endothelial Dysfunction and Thrombosis Formation? The Secret of COVID-19

The world is in a hard battle against COVID-19. Endothelial cells are among the most critical targets of SARS-CoV-2. Dysfunction of endothelium leads to vascular injury following by coagulopathies and thrombotic conditions in the vital organs increasing the risk of life-threatening events. Growing evidences revealed that endothelial dysfunction and consequent thrombotic conditions are associated with the severity of outcomes. It is not yet fully clear that these devastating sequels originate directly from the virus or a side effect of virus-induced cytokine storm. Due to endothelial dysfunction, plasma levels of some biomarkers are changed and relevant clinical manifestations appear as well. Stabilization of endothelial integrity and supporting its function are among the promising therapeutic strategies. Other than respiratory, COVID-19 could be called a systemic vascular disease and this aspect should be scrutinized in more detail in order to reduce related mortality. In the present investigation, the effects of COVID-19 on endothelial function and thrombosis formation are discussed. In this regard, critical players, laboratory findings, clinical manifestation, and suggestive therapies are presented.

"Ways in which the neonatal Fc-receptor is involved in autoimmunity"

Since the neonatal IgG Fc receptor (FcRn) was discovered, its role has evolved from immunoglobulin recycling and biodistribution to antigen presentation and immune complex routing, bringing it to the center of both humoral and cellular immune responses. FcRn is thus involved in the pathophysiology of immune-related diseases such as cancer, infection, and autoimmune disorders. This review focuses on the role of FcRn in autoimmunity, based on the available data from both animal models and human studies. The knowledge concerning ways in which FcRn is involved in autoimmune response has led to the development of inhibitors for the treatment of autoimmune diseases, also described here. Up to date, the literature remains scarce, shedding light on the need for further studies to fully understand the various pathophysiological roles of this unique receptor.

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FcRn is an intracellular receptor with a key role in IgG and immune complex management.

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FcRn-targeting therapies are a promising way of treatment in antibodies mediated diseases.

Mechanisms of SARS-CoV-2-induced lung vascular disease: potential role of complement

The outbreak of COVID-19 disease, caused by SARS-CoV-2 beta-coronovirus, urges a focused search for the underlying mechanisms and treatment options. The lung is the major target organ of COVID-19, wherein the primary cause of mortality is hypoxic respiratory failure, resulting from acute respiratory distress syndrome, with severe hypoxemia, often requiring assisted ventilation. While similar in some ways to acute respiratory distress syndrome secondary to other causes, lungs of some patients dying with COVID-19 exhibit distinct features of vascular involvement, including severe endothelial injury and cell death via apoptosis and/or pyroptosis, widespread capillary inflammation, and thrombosis. Furthermore, the pulmonary pathology of COVID-19 is characterized by focal inflammatory cell infiltration, impeding alveolar gas exchange resulting in areas of local tissue hypoxia, consistent with potential amplification of COVID-19 pathogenicity by hypoxia. Vascular endothelial cells play essential roles in both innate and adaptive immune responses, and are considered to be "conditional innate immune cells" centrally participating in various inflammatory, immune pathologies. Activated endothelial cells produce cytokines/chemokines, dynamically recruit and activate inflammatory cells and platelets, and centrally participate in pro-thrombotic processes (thrombotic microangiopathies). Initial reports presented pathological findings of localized direct infection of vascular endothelial cells with SARS-CoV-2, yet emerging evidence does not support direct infection of endothelial or other vascular wall cell and thus widespread endothelial cell dysfunction and inflammation may be better explained as secondary responses to epithelial cell infection and inflammation. Endothelial cells are also actively engaged in a cross-talk with the complement system, the essential arm of innate immunity. Recent reports present evidence for complement deposition in SARS-CoV-2-damaged lung microcirculation, further strengthening the idea that, in severe cases of COVID-19, complement activation is an essential player, generating destructive hemorrhagic, capillaritis-like tissue damage, clotting, and hyperinflammation. Thus, complement-targeted therapies are actively in development. This review is intended to explore in detail these ideas.

Ginkgolide C attenuates lipopolysaccharide‑induced acute lung injury by inhibiting inflammation via regulating the CD40/NF‑κB signaling pathway

Excessive lung inflammation caused by endotoxins, including lipopolysaccharide (LPS), mediates the detrimental effects of acute lung injury (ALI), as evidenced by severe alveolar epithelial cell injury. CD40, a member of the tumor necrosis factor receptor superfamily, serves as a central activator in triggering and transducing a series of severe inflammatory events during the pathological processes of ALI. Ginkgolide C (GC) is an efficient and specific inhibitor of CD40. Therefore, the present study aimed to investigate whether GC alleviated LPS‑induced ALI, as well as the potential underlying mechanisms. LPS‑injured wild‑type and CD40 gene conditional knockout mice, and primary cultured alveolar epithelial cells isolated from these mice served as in vivo and in vitro ALI models, respectively. In the present study, histopathological assessment, polymorphonuclear neutrophil (PMN) infiltration, lung injury score, myeloperoxidase activity, wet‑to‑dry (W/D) weight ratio and hydroxyproline (Hyp) activity were assessed to evaluate lung injury. In addition, immunohistochemistry was performed to evaluate intracellular adhesion molecule‑1, vascular cell adhesion molecule‑1 and inducible nitric oxide synthase expression levels, and TNF‑α, IL‑1β, IL‑6 ELISAs and western blotting were conducted to elucidate the signaling pathway. The results demonstrated that GC alleviated LPS‑induced lung injury, as evidenced by improvements in ultrastructural characteristics and histopathological alterations of lung tissue, inhibited PMN infiltration, as well as reduced lung injury score, W/D weight ratio and hydroxyproline content. In LPS‑injured alveolar epithelial cells, GC significantly reduced IκBα phosphorylation, IKKβ activity and NF‑κB p65 subunit translocation via downregulating CD40, leading to a significant decrease in downstream inflammatory cytokine levels and protein expression levels. In conclusion, the results of the present study demonstrated that GC displayed a protective effect against LPS‑induced ALI via inhibition of the CD40/NF‑κB signaling pathway; therefore, the present study suggested that the CD40/NF‑κB signaling pathway might serve as a potential therapeutic target for ALI.

Biomarkers for acute and chronic graft versus host disease: state of the art

INTRODUCTION

Despite significant advances in treatment and prevention, graft-versus-host disease (GVHD) still represents the main cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Thus, considerable research efforts have been made to find and validate reliable biomarkers for diagnosis, prognosis, and risk stratification of GVHD.

AREAS COVERED

In this review the most recent evidences on different types of biomarkers studied for GVHD, such as genetic, plasmatic, cellular markers, and those associated with microbiome, were summarized. A comprehensive search of peer-review literature was performed in PubMed including meta-analysis, preclinical and clinical trials, using the terms: cellular and plasma biomarkers, graft-versus-host disease, cytokines, and allogeneic hematopoietic stem cell transplantation.

EXPERT OPINION

In the near future, several validated biomarkers will be available to help clinicians in the diagnosis of GVHD, the identification of patients at high risk of GVHD development and in patients' stratification according to its severity. Then, immunosuppressive treatment could be tailored to each patient's real needs. However, more efforts are needed to achieve this goal. Although most of the proposed biomarkers currently lack validation with large-scale clinical data, their study led to improved knowledge of the biological basis of GVHD, and ultimately to implementation of GHVD treatment.

Homeostatic and early-recruited CD101- eosinophils suppress endotoxin-induced acute lung injury

INTRODUCTION

Acute lung injury (ALI) is a fatal but undertreated condition with severe neutrophilic inflammation, although little is known about the functions of eosinophils in the pathogenesis of ALI. Our objectives were to investigate the roles and molecular mechanisms of eosinophils in ALI.

METHODS

Pulmonary eosinophils were identified by flow cytometry. Mice with abundant or deficient eosinophils were used. Cellularity of eosinophils and neutrophils in bronchoalveolar lavage fluid, inflammatory assessment, and survival rate were determined. Human samples were also used for validating experimental results.

RESULTS

Blood eosinophils were increased in surviving patients with acute respiratory distress syndrome (ARDS) independent of corticosteroid usage. There existed homeostatic eosinophils in lung parenchyma in mice and these homeostatic eosinophils, originating from the bone marrow, were predominantly CD101^-. More CD101^- eosinophils could be recruited earlier than lipopolysaccharide (LPS)-initiated neutrophilic inflammation. Loss of eosinophils augmented LPS-induced pulmonary injury. Homeostatic CD101^- eosinophils ameliorated, while allergic CD101⁺ eosinophils exacerbated, the neutrophilic inflammation induced by LPS. Likewise, CD101 expression in eosinophils from ARDS patients did not differ from healthy subjects. Mechanistically, CD101^- eosinophils exhibited higher levels of Alox15 and Protectin D1. Administration of Protectin D1 isomer attenuated the neutrophilic inflammation.

CONCLUSIONS

Collectively, our findings identify an uncovered function of native CD101^- eosinophils in suppressing neutrophilic lung inflammation and suggest a potential therapeutic target for ALI.

I mmunosenescence and Inflammaging: Risk Factors of Severe COVID-19 in Older People

Old individuals are more susceptible to various infections due to immunological changes that occur during the aging process. These changes named collectively as "immunosenescence" include decreases in both the innate and adaptive immune responses in addition to the exacerbated production of inflammatory cytokines. This scenario of immunological dysfunction and its relationship with disease development in older people has been widely studied, especially in infections that can be fatal, such as influenza and, more recently, COVID-19. In the current scenario of SARS-CoV-2 infection, many mechanisms of disease pathogenesis in old individuals have been proposed. To better understand the dynamics of COVID-19 in this group, aspects related to immunological senescence must be well elucidated. In this article, we discuss the main mechanisms involved in immunosenescence and their possible correlations with the susceptibility of individuals of advanced age to SARS-CoV-2 infection and the more severe conditions of the disease.

A consideration of convalescent plasma and plasma derivatives in the care of Severely-ill patients with COVID-19

The pathogenesis and immunopathological damage of severe forms of COVID-19 resemble acute autoimmune disease sparked by SARS-CoV-2, including an early systemic overproduction of proinflammatory cytokines. Such immunopathological features provide a rationale for the use of passive immunotherapy with convalescent plasma as a source of neutralizing anti-viral antibodies and of anti-inflammatory plasma components. While convalescent plasma therapy is now being evaluated in prospective clinical trials, we further consider the therapeutic potential of human hyper immune globulins, and of heterologous, engineered and monoclonal neutralizing antibodies as anti-viral agents to treat COVID-19. Good medical practice procedures are still needed and is why we also discuss the potential use of polyclonal polyspecific immunoglobulins (IVIG), a therapeutic plasma derivative, with potent anti-inflammatory activity, in severe forms of Covid-19.

Structural characteristics of circulating immune complexes in calves with bronchopneumonia: Impact on the quiescent leukocytes

Calf bronchopneumonia is accompanied by increased level of circulating immune complexes (CIC), and we analysed size, and protein and lipid constituents of these CIC with an attempt to elucidate the connection between the CIC structural properties and their capacity to modulate leukocyte function. CIC of heathy calves (CIC_H) and calves with naturally occurring bronchopneumonia (CIC_D) were isolated by PEG precipitation and analysed by electrophoresis and chromatography. The predominant CIC proteins were IgG, albumin, and transferrin. Affinity isolated serum and CIC IgG coprecipitated several proteins, but only 75 and 80 kDa proteins bound CIC IgG, exclusively. 60 and 65 kDa proteins co-precipitated with CIC_D IgG, unlike CIC_H IgG. In both CIC_H and CIC_D, oleic acid-containing phospholipids predominated. In CIC_D, the content of oleic and vaccenic acid was higher than in CIC_H, while myristic, palmitic, stearic, linoleic and arachidonic acid showed lower content. Dynamic light scattering displayed difference in particle size distribution between CIC_H and CIC_D; 1280 nm large particles were present only in CIC_D. The effect of CIC_H and CIC_D on mononuclear cells (MNC) and granulocytes was analysed in vitro. CIC_H and CIC_D, with slight difference in intensity, stimulate MNC apoptosis, promote cell cycle arrest of unstimulated MNC, and cell cycle progression of PHA stimulated MNC. Both CIC reduced granulocyte apoptosis after 24 h while after 48 h this effect was detected for CIC_D only. These results indicate that structural differences of CIC_H and CIC_D might interfere with the CIC functional capacity, which we consider important for evaluation of CIC immunoregulatory function.

COVID-19-driven endothelial damage: complement, HIF-1, and ABL2 are potential pathways of damage and targets for cure

COVID-19 pandemia is a major health emergency causing hundreds of deaths worldwide. The high reported morbidity has been related to hypoxia and inflammation leading to endothelial dysfunction and aberrant coagulation in small and large vessels. This review addresses some of the pathways leading to endothelial derangement, such as complement, HIF-1α, and ABL tyrosine kinases. This review also highlights potential targets for prevention and therapy of COVID-19-related organ damage and discusses the role of marketed drugs, such as eculizumab and imatinib, as suitable candidates for clinical trials.

Neutrophil FcγRIIA promotes IgG-mediated glomerular neutrophil capture via Abl/Src kinases

The kidney glomerular capillaries are frequent sites of immune complex deposition and subsequent neutrophil accumulation in post-infectious and rapidly progressive glomerulonephritis. However, the mechanisms of neutrophil recruitment remain enigmatic, and there is no targeted therapeutic to avert this proximal event in glomerular inflammation. The uniquely human activating Fc receptor FcγRIIA promotes glomerular neutrophil accumulation and damage in anti-glomerular basement membrane-induced (anti-GBM-induced) glomerulonephritis when expressed on murine neutrophils. Here, we found that neutrophils are directly captured by immobilized IgG antibodies under physiological flow conditions in vitro through FcγRIIA-dependent, Abl/Src tyrosine kinase-mediated F-actin polymerization. Biophysical measurements showed that the lifetime of FcγRIIA-IgG bonds increased under mechanical force in an F-actin-dependent manner, which could enable the capture of neutrophils under physiological flow. Kidney intravital microscopy revealed that circulating neutrophils, which were similar in diameter to glomerular capillaries, abruptly arrested following anti-GBM antibody deposition via neutrophil FcγRIIA and Abl/Src kinases. Accordingly, inhibition of Abl/Src with bosutinib reduced FcγRIIA-mediated glomerular neutrophil accumulation and renal injury in experimental, crescentic anti-GBM nephritis. These data identify a pathway of neutrophil recruitment within glomerular capillaries following IgG deposition that may be targeted by bosutinib to avert glomerular injury.