A plea for the pathogenic role of immune complexes in severe Covid-19

Complement and COVID-19: Three years on, what we know, what we don't know, and what we ought to know

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus was identified in China in 2019 as the causative agent of COVID-19, and quickly spread throughout the world, causing over 7 million deaths, of which 2 million occurred prior to the introduction of the first vaccine. In the following discussion, while recognising that complement is just one of many players in COVID-19, we focus on the relationship between complement and COVID-19 disease, with limited digression into directly-related areas such as the relationship between complement, kinin release, and coagulation. Prior to the 2019 COVID-19 outbreak, an important role for complement in coronavirus diseases had been established. Subsequently, multiple investigations of patients with COVID-19 confirmed that complement dysregulation is likely to be a major driver of disease pathology, in some, if not all, patients. These data fuelled evaluation of many complement-directed therapeutic agents in small patient cohorts, with claims of significant beneficial effect. As yet, these early results have not been reflected in larger clinical trials, posing questions such as who to treat, appropriate time to treat, duration of treatment, and optimal target for treatment. While significant control of the pandemic has been achieved through a global scientific and medical effort to comprehend the etiology of the disease, through extensive SARS-CoV-2 testing and quarantine measures, through vaccine development, and through improved therapy, possibly aided by attenuation of the dominant strains, it is not yet over. In this review, we summarise complement-relevant literature, emphasise its main conclusions, and formulate a hypothesis for complement involvement in COVID-19. Based on this we make suggestions as to how any future outbreak might be better managed in order to minimise impact on patients.

Immune system disturbances after a new coronavirus infection COVID-19

During the pandemic, a large number of works devoted to COVID infection have appeared, which have made it possible to understand the pathogenetic features of the disease and to accumulate significant clinical experience. However, the question remains about the degree of participation of humoral and cellular (primarily T-cell) immunity in the mechanisms of immune defense and resistance to COVID-19, the individual features of the immune response in different subjects. Post-COVID syndrome is currently a separate diagnosis included in the ICD-10 International Classification of Diseases, but the long-term effects of the SARS-CoV-2 on the immune system are not yet well established. At the same time, a long-term increased activity of the immune system can contribute to the development of autoimmune reactions. The review of the literature presents the results of studies, mainly devoted to immune system disorders after COVID infection. The changes in subpopulations of T-lymphocytes, B-lymphocytes, their functional properties, the complement system and other factors of humoral immunity, as well as the production of a number of cytokines are described. Data on immune disorders in post-COVID syndrome and during the convalescence period are presented in detail. Since COVID-19 is an infection that has a significant impact on the hematopoietic system and hemostasis, special attention is paid to the category of subjects with an increased risk of severe complications. Among the latter are elderly patients, persons suffering from diabetes mellitus, oncological and oncohematological patients, in particular, with hematopoietic and lymphoid tissue neoplasia, such as chronic lymphocytic leukemia, lymphoma, multiple myeloma. The review pays special attention to the peculiarities of the course of COVID-19 and the response of the immune system to vaccination in patients with oncohematological diseases. Deciphering the significance of individual links of cellular and humoral immunity in patients who have undergone COVID-19 is an important issue in creating effective vaccines and improving therapeutic methods.

Persistent but dysfunctional mucosal SARS-CoV-2-specific IgA and low lung IL-1β associate with COVID-19 fatal outcome: A cross-sectional analysis

The role of the mucosal pulmonary antibody response in coronavirus disease 2019 (COVID-19) outcome remains unclear. Here, we found that in bronchoalveolar lavage (BAL) samples from 48 patients with severe COVID-19-infected with the ancestral Wuhan virus, mucosal IgG and IgA specific for S1, receptor-binding domain (RBD), S2, and nucleocapsid protein (NP) emerged in BAL containing viruses early in infection and persist after virus elimination, with more IgA than IgG for all antigens tested. Furthermore, spike-IgA and spike-IgG immune complexes were detected in BAL, especially when the lung virus has been cleared. BAL IgG and IgA recognized the four main RBD variants. BAL neutralizing titers were higher early in COVID-19 when virus replicates in the lung than later in infection after viral clearance. Patients with fatal COVID-19, in contrast to survivors, developed higher levels of mucosal spike-specific IgA than IgG but lost neutralizing activities over time and had reduced IL-1β in the lung. Altogether, mucosal spike and NP-specific IgG and S1-specific IgA persisting after lung severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) clearance and low pulmonary IL-1β correlate with COVID-19 fatal outcome. Thus, mucosal SARS-CoV-2-specific antibodies may have adverse functions in addition to protective neutralization.

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.

OUP accepted manuscript

Although a high prevalence of COVID-19-associated pulmonary aspergillosis has been reported, it is still difficult to distinguish between colonization with Aspergillus fumigatus and infection. Concomitantly, similarities between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and hypersensitivity pneumonitis were suggested. The objective of this study was to investigate retrospectively if precipitin assays targeting A. fumigatus could have been useful in the management of SARS-CoV-2 patients hospitalized in an Intensive Care Unit (ICU) in 2020. SARS-CoV-2 ICU patients were screened for Aspergillus co-infection using biomarkers (galactomannan antigen, qPCR) and culture of respiratory samples (tracheal aspirates and bronchoalveolar lavage). For all these patients, clinical data, ICU characteristics and microbial results were collected. Electrosyneresis assays were performed using commercial A. fumigatus somatic and metabolic antigens. ELISA were performed using in-house A. fumigatus purified antigen and recombinant antigens.

Our study population consisted of 65 predominantly male patients, with a median ICU stay of 22 days, and a global survival rate of 62%. Thirty-five patients had at least one positive marker for Aspergillus species detection. The number of arcs obtained by electrosyneresis using the somatic A. fumigatus antigen was significantly higher for these 35 SARS-CoV-2 ICU patients (P 0.01, Welch's t-test). Our study showed that SARS-CoV-2 ICU patients with a positive marker for Aspergillus species detection more often presented precipitins towards A. fumigatus. Serology assays could be an additional tool to assess the clinical relevance of the Aspergillus species in respiratory samples of SARS-CoV-2 ICU patients.

Immune response to SARS-CoV-2 Variants: A focus on severity, susceptibility, and preexisting immunity

The heterogeneous phenotypes among patients with coronavirus disease 2019 (COVID-19) has drawn worldwide attention, especially those with severe symptoms without comorbid conditions. Immune responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative virus of COVID-19, occur mainly by the innate immune response via the interferon (IFN)-mediated pathways, and the adaptive immunity via the T lymphocyte and the antibody mediated pathways. The ability of the original Wuhan SARS-CoV-2 strain, and possibly more so with new emerging variants, to antagonize IFN-mediated antiviral responses can be behind the higher early viral load, higher transmissibility, and milder symptoms compared to SARS-CoV and are part of the continued clinical evolution of COVID-19. Since it first emerged, several variants of SARS-CoV-2 have been circulating worldwide. Variants that have the potential to elude natural or vaccine-mediated immunity are variants of concern. This review focuses on the main host factors that may explain the immune responses to SARS-CoV-2 and its variants in the context of susceptibility, severity, and preexisting immunity.

Therapeutic plasma exchange followed by convalescent plasma transfusion in severe and critically ill COVID-19 patients: A single centre non-randomized controlled trial

Therapeutic plasma exchange (TPE) has been proposed as a rescue therapy in critically ill COVID-19 patients. The aim of the present study was to determine whether combining TPE with convalescent plasma (CVP) transfusion early in the intensive care unit (ICU) stay improves survival among this heterogeneous population. The primary endpoint was survival at 30 days. Secondary endpoints included assessing the evolution of biomarkers, such as the partial pressure of arterial oxygen to fractional inspired oxygen ratio, and C reactive protein (CRP), lactate dehydrogenase (LDH) and ferritin levels at the 7-day follow-up. This single centre, prospective, non-randomized controlled trial was conducted in an 8-bed COVID-19 ICU and included patients with severe COVID-19 pneumonia requiring intensive care treatment. A total of 19 patients were treated by performing TPE followed by CVP transfusion, in addition to standard treatment, while for another 19 patients, only standard treatment according to hospital protocols was used. TPE was initiated during the first 24 h after ICU admission, followed immediately by transfusion of CVP. Survival at 30 days was 47.37% in the TPE CVP group and 26.32% in the control group (P=0.002). Patients in the TPE CVP group also showed better oxygenation and a reduction in inflammation, with decreased CRP, LDH and ferritin levels compared with those in the control group. Overall, the study indicated that early initiation of TPE followed by CVP transfusion may be a valid rescue therapy in severe and critically ill COVID-19 patients, with a statistically significant survival benefit, improved oxygenation and a reduction in inflammatory markers. The trial was registered in the ClinicalTrials.gov database (trial registration number: NCT04973488) on July 22, 2021 (retrospectively registered).

Genetic susceptibility of COVID-19: a systematic review of current evidence

INTRODUCTION

While COVID-19 pandemic continues to spread worldwide, researchers have linked patterns of traits to poor disease outcomes. Risk factors for COVID-19 include asthma, elderly age, being pregnant, having any underlying diseases such as cardiovascular disease, diabetes, obesity, and experiencing lifelong systemic racism. Recently, connections to certain genes have also been found, although the susceptibility has not yet been established. We aimed to investigate the available evidence for the genetic susceptibility to COVID-19.

METHODS

This study was a systematic review of current evidence to investigate the genetic susceptibility of COVID-19. By systematic search and utilizing the keywords in the online databases including Scopus, PubMed, Web of Science, and Science Direct, we retrieved all the related papers and reports published in English from December 2019 to September 2020.

RESULTS

According to the findings, COVID-19 uses the angiotensin-converting enzyme 2 (ACE2) receptor for cell entry. Previous studies have shown that people with ACE2 polymorphism who have type 2 transmembrane serine proteases (TMPRSS2) are at high risk of SARS-CoV-2 infection. Also, two studies have shown that males are more likely to become infected with SARS-CoV-2 than females. Besides, research has also shown that patients possessing HLA-B*15:03 genotype may become immune to the infection.

CONCLUSION

Combing through the genome, several genes related to immune system's response were related to the severity and susceptibility to the COVID-19. In conclusion, a correlation was found between the ACE2 levels and the susceptibility to SARS-CoV-2 infection.

Genetic justification of severe COVID-19 using a rigorous algorithm

Recent studies suggest excessive complement activation in severe coronavirus disease-19 (COVID-19). The latter shares common characteristics with complement-mediated thrombotic microangiopathy (TMA). We hypothesized that genetic susceptibility would be evident in patients with severe COVID-19 (similar to TMA) and associated with disease severity. We analyzed genetic and clinical data from 97 patients hospitalized for COVID-19. Through targeted next-generation-sequencing we found an ADAMTS13 variant in 49 patients, along with two risk factor variants (C3, 21 patients; CFH,34 patients). 31 (32%) patients had a combination of these, which was independently associated with ICU hospitalization (p = 0.022). Analysis of almost infinite variant combinations showed that patients with rs1042580 in thrombomodulin and without rs800292 in complement factor H did not require ICU hospitalization. We also observed gender differences in ADAMTS13 and complement-related variants. In light of encouraging results by complement inhibitors, our study highlights a patient population that might benefit from early initiation of specific treatment.

Liver histopathology in COVID-19 patients: A mono-Institutional series of liver biopsies and autopsy specimens

Few studies have focused on COVID-19 patients’ hepatic histopathological features. Many of the described morphological landscapes are non-specific and possibly due to other comorbidities or to Sars-CoV-2-related therapies. We describe the hepatic histopathological findings of 3 liver biopsies obtained from living COVID-19 patients in which active SARS-CoV-2 infection was molecularly confirmed and biopsied because of significant alterations of liver function tests and 25 livers analyzed during COVID-19-related autopsies. Main histopathological findings were (i) the absence of significant biliary tree or vascular damages, (ii) mild/absent lymphocytic hepatitis; (iii) activation of (pigmented) Kupffer cells, (iv) hepatocellular regenerative changes, (v) the presence of steatosis, (vi) sinusoidal ectasia, micro-thrombosis and acinar atrophy in autopsy specimens No viral particle actively infecting the hepatic or endothelial cells was detected at in situ hybridization. The morphological features observed within the hepatic parenchyma are not specific and should be considered as the result of an indirect insult resulting from the viral infection or the adopted therapeutic protocols.

Morphology and Composition of Immunodiffusion Precipitin Complexes Evaluated via Microscopy and Proteomics

New approaches to rapid, simple, in vitro diagnostic immunoassays that do not rely on centralized laboratory facilities are urgently needed for disease diagnosis and to inform treatment strategies. The recent and ongoing COVID-19 pandemic has emphasized that rapid diagnostics are needed to help guide government policies on quarantines, social distancing measures, and community lockdowns. A common approach to developing new immunoassays is to modify existing platforms (e.g., automated ELISA and lateral flow assays) for the new analyte, even though this does not address the drawbacks of existing platforms. An alternate approach is to search for robust assays that have been superseded but could in fact solve important challenges using modern technologies. Immunodiffusion is one such platform based on unique "precipitin ring" patterns formed in gels or paper following interactions between proteins and cognate antibodies in diffusion/reaction systems. Herein, we investigate the microstructure of these precipitin rings using a combination of fluorescence and electron microscopy and also perform a mass spectrometry investigation to determine the proteomic composition of the rings. We observed that the rings were composed of microparticles, which we termed "precipitin complexes", and that these complexes were composed of at least 19 key proteins, including immunoglobulins and complement factors along with a range of plasma proteins, possibly related to immune complexes and/or high-density lipoprotein particles. This information will be useful in developing new in vitro diagnostics using reaction/diffusion systems-techniques that require a single assay step and that only require calibrated length measurements for target protein quantification.

De novo design, retrosynthetic analysis and combinatorial synthesis of a hybrid antiviral (VTAR-01) to inhibit the interaction of SARS-CoV2 spike glycoprotein with human angiotensin-converting enzyme 2

SARS-like coronavirus (SARS-CoV2) has emerged as a global threat to humankind and is rapidly spreading. The infectivity, pathogenesis and infection of this virus are dependent on the interaction of SARS-CoV2 spike protein with human angiotensin converting enzyme 2 (hACE2). Spike protein contains a receptor-binding domain (RBD) that recognizes hACE-2. In the present study, we are reporting a de novo designed novel hybrid antiviral ‘VTAR-01’ molecule that binds at the interface of RBD-hACE2 interaction. A series of antiviral molecules were tested for binding at the interface of RBD-hACE2 interaction. In silico screening, molecular mechanics and molecular dynamics simulation (MDS) analysis suggest ribavirin, ascorbate, lopinavir and hydroxychloroquine have strong interaction at the RBD-hACE2 interface. These four molecules were used for de novo fragment-based antiviral design. De novo designing, docking and MDS analysis identified a ‘VTAR’ hybrid molecule that has better interaction with this interface than all of the antivirals used to design it. We have further used retrosynthetic analysis and combinatorial synthesis to design 100 variants of VTAR molecules. Retrosynthetic analysis and combinatorial synthesis, along with docking and MDS, identified that VTAR-01 interacts with the interface of the RBD-ACE2 complex. MDS analysis confirmed its interaction with the RBD-ACE2 interface by involving Glu35 and Lys353 of ACE2, as well as Gln493 and Ser494 of RBD. Interaction of spike protein with ACE2 is essential for pathogenesis and infection of this virus; hence, this in silico designed hybrid antiviral molecule (VTAR-01) that binds at the interface of RBD-hACE2 may be further developed to control the infection of SARS-CoV2.

Summary: SARS-CoV2 has caused an outbreak globally and is responsible for high mortality and morbidity. Interaction of the receptor-binding domain of spike protein of this virus with human angiotensin converting enzyme (ACE2) is vital for the infection. Hence, a de novo designed hybrid antiviral molecule (VTAR-01) targeting RBD-ACE2 interaction may play a very significant role in controlling the COVID-19 disease.