Human poly- and cross-reactive anti-viral antibodies and their impact on protection and pathology

Malaria and other infections induce polyreactive antibodies that impact SARS-CoV-2 seropositivity estimations in endemic settings

Anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence is used to estimate the proportion of individuals within a population previously infected, to track viral transmission, and to monitor naturally and vaccine-induced immune protection. However, in sub-Saharan African settings, antibodies induced by higher exposure to pathogens may increase unspecific seroreactivity to SARS-CoV-2 antigens, resulting in false positive responses. To investigate the level and type of unspecific seroreactivitiy to SARS-CoV-2 in Africa, we measured immunoglobulin G (IgG), IgA, and IgM to a broad panel of antigens from different pathogens by Luminex in 602 plasma samples from African and European subjects differing in coronavirus disease 2019, malaria, and other exposures. Seroreactivity to SARS-CoV-2 antigens was higher in prepandemic African than in European samples and positively correlated with antibodies against human coronaviruses, helminths, protozoa, and especially Plasmodium falciparum. African subjects presented higher levels of autoantibodies, a surrogate of polyreactivity, which correlated with P. falciparum and SARS-CoV-2 antibodies. Finally, we found an improved sensitivity in the IgG assay in African samples when using urea as a chaotropic agent. In conclusion, our data suggest that polyreactive antibodies induced mostly by malaria are important mediators of the unspecific anti-SARS-CoV-2 responses, and that the use of dissociating agents in immunoassays could be useful for more accurate estimates of SARS-CoV-2 seroprevalence in African settings.

Role of auto-antibodies in the mechanisms of dengue pathogenesis and its progression: a comprehensive review

A complex interaction among virulence factors, host-genes and host immune system is considered to be responsible for dengue virus (DENV) infection and disease progression. Generation of auto-antibodies during DENV infection is a major phenomenon that plays a role in the pathophysiology of dengue hemorrhagic fever and dengue shock syndrome. Hemostasis, thrombocytopenia, hepatic endothelial dysfunction, and autoimmune blistering skin disease (pemphigus) are different clinical manifestations of dengue pathogenesis; produced due to the molecular mimicry of DENV proteins with self-antigens like coagulation factors, platelets and endothelial cell proteins. This review elaborately describes the current advancements in auto-antibody-mediated immunopathogenesis which inhibits coagulation cascade and promotes hyperfibrinolysis. Auto-antibodies like anti-endothelial cell antibodies-mediated hepatic inflammation during severe DENV infection have also been discussed. Overall, this comprehensive review provides insight to target auto-antibodies that may act as potential biomarkers for disease severity, and a ground for the development of therapeutic strategy against DENV.

Preexisting antibodies targeting SARS-CoV-2 S2 cross-react with commensal gut bacteria and impact COVID-19 vaccine induced immunity

The origins of preexisting SARS-CoV-2 cross-reactive antibodies and their potential impacts on vaccine efficacy have not been fully clarified. In this study, we demonstrated that S2 was the prevailing target of the preexisting S protein cross-reactive antibodies in both healthy human and SPF mice. A dominant antibody epitope was identified on the connector domain of S2 (1147-SFKEELDKYFKNHT-1160, P144), which could be recognized by preexisting antibodies in both human and mouse. Through metagenomic sequencing and fecal bacteria transplant, we demonstrated that the generation of S2 cross-reactive antibodies was associated with commensal gut bacteria. Furthermore, six P144 reactive monoclonal antibodies were isolated from naïve SPF mice and were proven to cross-react with commensal gut bacteria collected from both human and mouse. A variety of cross-reactive microbial proteins were identified using LC-MS, of which E. coli derived HSP60 and HSP70 proteins were confirmed to be able to bind to one of the isolated monoclonal antibodies. Mice with high levels of preexisting S2 cross-reactive antibodies mounted higher S protein specific binding antibodies, especially against S2, after being immunized with a SARS-CoV-2 S DNA vaccine. Similarly, we found that levels of preexisting S2 and P144-specific antibodies correlated positively with RBD binding antibody titers after two doses of inactivated SARS-CoV-2 vaccination in human. Collectively, our study revealed an alternative origin of preexisting S2-targeted antibodies and disclosed a previously neglected aspect of the impact of gut microbiota on host anti-SARS-CoV-2 immunity.

Hantavirus infection-induced B cell activation elevates free light chains levels in circulation

In humans, orthohantaviruses can cause hemorrhagic fever with renal syndrome (HFRS) or hantavirus pulmonary syndrome (HPS). An earlier study reported that acute Andes virus HPS caused a massive and transient elevation in the number of circulating plasmablasts with specificity towards both viral and host antigens suggestive of polyclonal B cell activation. Immunoglobulins (Igs), produced by different B cell populations, comprise heavy and light chains; however, a certain amount of free light chains (FLCs) is constantly present in serum. Upregulation of FLCs, especially clonal species, associates with renal pathogenesis by fibril or deposit formations affecting the glomeruli, induction of epithelial cell disorders, or cast formation in the tubular network. We report that acute orthohantavirus infection increases the level of Ig FLCs in serum of both HFRS and HPS patients, and that the increase correlates with the severity of acute kidney injury in HFRS. The fact that the kappa to lambda FLC ratio in the sera of HFRS and HPS patients remained within the normal range suggests polyclonal B cell activation rather than proliferation of a single B cell clone. HFRS patients demonstrated increased urinary excretion of FLCs, and we found plasma cell infiltration in archival patient kidney biopsies that we speculate to contribute to the observed FLC excreta. Analysis of hospitalized HFRS patients’ peripheral blood mononuclear cells showed elevated plasmablast levels, a fraction of which stained positive for Puumala virus antigen. Furthermore, B cells isolated from healthy donors were susceptible to Puumala virus in vitro, and the virus infection induced increased production of Igs and FLCs. The findings propose that hantaviruses directly activate B cells, and that the ensuing intense production of polyclonal Igs and FLCs may contribute to acute hantavirus infection-associated pathological findings.

Orthohantaviruses are globally spread zoonotic pathogens, which can cause hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) with significant burden to human health. The pathogenesis mechanisms of orthohantavirus-caused diseases are not known in detail; however, excessive immune response towards the virus with concomitant pathological effects against host tissues appears to be a contributing factor. Here we report an increase of free immunoglobulin (Ig) light chains (FLCs), components required to make complete Ig molecules, in blood of acute HFRS and HPS. Samples collected during acute HFRS demonstrated increased FLCs levels in the urine and blood of patients hospitalized due the disease. Furthermore, the FLC levels positively correlated with markers of acute kidney injury. In addition, our results show that orthohantaviruses can infect and activate B cells to produce FLCs as well as whole Igs, which provides a mechanistic explanation of the increased FLC levels in patients. Taken together, our results suggest that aberrant antibody responses might play a role in the pathogenesis of orthohantavirus infections.

Current Paradigms in COVID-19 Research: Proposed Treatment Strategies, Recent Trends and Future Directions

BACKGROUND

Recent pandemic of coronavirus disease caused by a novel coronavirus SARS-CoV-2 in humans is the third outbreak by this family of viruses leading to an acute respiratory infection, which has been a major cause of morbidity and mortality worldwide.The virus belongs to the genus, Betacoronavirus, which has been recently reported to have significant similarity (>89%) to a severe acute respiratory syndrome (SARS)-related member of the Sarbecoviruses. Current researches are not sufficient to understand the etiological and immunopathobiological parameters related to COVID-19 so as to have a therapeutic solution to the problem.

METHODS

A structured search of bibliographic databases for peer-reviewed research literature has been carried out using focused review questions and inclusion/exclusion criteria. Further Standard tools were implied in order to appraise the quality of retrieved papers. The characteristic outcomes of screened research and review articles along with analysis of the interventions and findings of included studies using a conceptual framework have been described employing a deductive qualitative content analysis methodology.

RESULTS

This review systematically summarizes the immune-pathobiological characteristics, diagnosis, potential therapeutic options for the treatment and prevention of COVID-19 based on the current published literature and evidence. The current review has covered 125 peerreviewed articles, the majority of which are from high-income technically developed countries providing the most recent updates about the current understanding of the COVID-19 bringing all the significant findings and related researches together at a single platform. In addition, possible therapeutic interventions, treatment strategies and vaccine development initiatives to manage COVID-19 have been proposed.

CONCLUSION

It is anticipated that this review would certainly assist the public in general and scientific community in particular to recognize and effectively deal with COVID-19, providing a reference guide for futuristic studies.

Polyreactive antibodies as potential humoral biomarkers of host resistance to cystic echinococcosis

Polyreactive antibodies (pAb) bind to a broad range of unrelated structures, providing hosts with functional components able to rapidly recognize and protect against different pathogens. However, their roles against helminth parasites are still unexplored. Here, pAb profiles were analysed in cystic echinococcosis (CE), a zoonosis caused by the cestode Echinococcus granulosus sensu lato. Levels of anti-DNP (2,4-dinitrophenyl-hapten) antibodies were measured as a surrogate parameter of pAb in different biological settings. Firstly, levels of serum and peritoneal pAb were measured during early experimental secondary CE, using both high (Balb/c) and low (C57Bl/6) susceptible mouse strains. Serum pAb mostly differed in normal mice, being pAb levels of IgG subclasses with poor anti-parasite activities predominant in Balb/c animals. Conversely, peritoneal pAb isotypes/subclasses with efficient anti-parasite activities predominated in normal and infected C57Bl/6 mice. Secondly, sera from potentially resistant patients, susceptible individuals and healthy donors were analysed, showing higher pAb levels of the IgA and IgG-particularly IgG1-isotypes in potentially resistant individuals compared to control groups. Finally, since remarkable differences were observed in pAb profiles according to the intrinsic host susceptibility to the infection, we proposed here that pAb might be considered as potential humoral biomarkers for host resistance to CE.

COVID-19 in India: Are Biological and Environmental Factors Helping to Stem the Incidence and Severity?

The ongoing Corona virus (COVID-19) pandemic has witnessed global political responses of unimaginable proportions. Many nations have implemented lockdowns that involve mandating citizens not to leave their residences for non-essential work. The Indian government has taken appropriate and commendable steps to curtail the community spread of COVID-19. While this may be extremely beneficial, this perspective discusses the other reasons why COVID-19 may have a lesser impact on India. We analyze the current pattern of SARS-CoV-2 transmission, testing, and mortality in India with an emphasis on the importance of mortality as a marker of the clinical relevance of COVID-19 disease. We also analyze the environmental and biological factors which may lessen the impact of COVID-19 in India. The importance of cross-immunity, innate immune responses, ACE polymorphism, and viral genetic mutations are discussed.

Antibody specificity and promiscuity

The immune system is capable of making antibodies against anything that is foreign, yet it does not react against components of self. In that sense, a fundamental requirement of the body's immune defense is specificity. Remarkably, this ability to specifically attack foreign antigens is directed even against antigens that have not been encountered a priori by the immune system. The specificity of an antibody for the foreign antigen evolves through an iterative process of somatic mutations followed by selection. There is, however, accumulating evidence that the antibodies are often functionally promiscuous or multi-specific which can lead to their binding to more than one antigen. An important cause of antibody cross-reactivity is molecular mimicry. Molecular mimicry has been implicated in the generation of autoimmune response. When foreign antigen shares similarity with the component of self, the antibodies generated could result in an autoimmune response. The focus of this review is to capture the contrast between specificity and promiscuity and the structural mechanisms employed by the antibodies to accomplish promiscuity, at the molecular level. The conundrum between the specificity of the immune system for foreign antigens on the one hand and the multi-reactivity of the antibody on the other has been addressed. Antibody specificity in the context of the rapid evolution of the antigenic determinants and molecular mimicry displayed by antigens are also discussed.

A multispecific monoclonal antibody G2 recognizes at least three completely different epitope sequences with high affinity

A monoclonal antibody (mAb) G2 possesses an unusual characteristic of reacting with at least three proteins (ATP6V1C1, SEPT3, and C6H10orf76) other than its original antigen, chicken prion protein (ChPrP). The epitopes on ChPrP and ATP6V1C1 have been identified previously. In this study, we identified the epitope in the third protein, SEPT3. Interestingly, there was no amino acid sequence similarity among the epitopes on the three proteins. These epitopes had high binding affinities to G2 (K_D  = ∼10^-7 M for monovalent binding and K_D  = ∼10^-9 M for divalent binding), as determined using a SPR biosensor. This is the first report on a three-in-one mAb recognizing completely different epitope sequences with high affinity. Additionally, competitive ELISA indicated that the binding sites on G2, specific for the three different epitopes, overlapped, suggesting that the antigen-binding site may be flexible in the free form and capable of adapting to at least three different conformations to enable interactions with three different antigens.

Autopolyreactivity Confers a Holistic Role in the Immune System

In this review, we summarize and discuss some key findings from the study of naturally occurring autoantibodies. The B-cell compartment of the immune system appears to recognize almost all endogenous and environmental antigens. This ability is accomplished principally through autopolyreactive humoral and cellular immune receptors. This extended autopolyreactivity (1) along immunoglobulin gene recombination contributes to the immune system's ability to recognize a very large number of self and non-self constituents; and (2) generates a vast immune network that creates communication channels between the organism's interior and exterior. Thus, the immune system continuously evolves depending on the internal and external stimuli it encounters. Furthermore, this far-reaching network's existence implies activities resembling those of classical biological factors or activities that modulate the function of other classical biological factors. A few such antibodies have already been found. Another important concept is that natural autoantibodies are highly dependent on the presence or absence of commensal microbes in the organism. These results are in line with past and recent findings showing the fundamental influence of the microbiota on proper immune system development, and necessitate the existence of a host-microbe homeostasis. This homeostasis requires that the participating humoral and cellular receptors are able to recognize self-antigens and commensal microbes without damaging them. Autopolyreactive immune receptors expressing low affinity for both types of antigens fulfil this role. The immune system appears to play a holistic role similar to that of the nervous system.

Lower IgG somatic hypermutation rates during acute dengue virus infection is compatible with a germinal center-independent B cell response

BACKGROUND

The study of human B cell response to dengue virus (DENV) infection is critical to understand serotype-specific protection and the cross-reactive sub-neutralizing response. Whereas the first is beneficial and thus represents the ultimate goal of vaccination, the latter has been implicated in the development of severe disease, which occurs in a small, albeit significant, fraction of secondary DENV infections. Both primary and secondary infections are associated with the production of poly-reactive and cross-reactive IgG antibodies.

METHODS

To gain insight into the effect of DENV infection on the B cell repertoire, we used VH region high-throughput cDNA sequencing of the peripheral blood IgG B cell compartment of 19 individuals during the acute phase of infection. For 11 individuals, a second sample obtained 6 months later was analyzed for comparison. Probabilities of sequencing antibody secreting cells or memory B cells were estimated using second-order Monte Carlo simulation.

RESULTS

We found that in acute disease there is an increase in IgG B cell diversity and changes in the relative use of segments IGHV1-2, IGHV1-18, and IGHV1-69. Somewhat unexpectedly, an overall low proportion of somatic hypermutated antibody genes was observed during the acute phase plasmablasts, particularly in secondary infections and those cases with more severe disease.

CONCLUSIONS

Our data are consistent with an innate-like antiviral recognition system mediated by B cells using defined germ-line coded B cell receptors, which could provide a rapid germinal center-independent antibody response during the early phase of infection. A model describing concurrent T-dependent and T-independent B cell responses in the context of DENV infection is proposed, which incorporates the selection of B cells using hypomutated IGHV segments and their potential role in poly/cross-reactivity. Its formal demonstration could lead to a definition of its potential implication in antibody-dependent enhancement, and may contribute to rational vaccine development efforts.

Tetravalent dengue DIIIC protein together with alum and ODN elicits a Th1 response and neutralizing antibodies in mice

Dengue disease is a global challenge for healthcare systems particularly during outbreaks, and millions of dollars are spent every year for vector control. An efficient and safe vaccine that is cost-effective could resolve the burden that dengue virus imposes on affected countries. We describe here the immunogenicity of a tetravalent formulation of a recombinant fusion protein consisting of E domain III and the capsid protein of dengue serotypes 1-4 (Tetra DIIIC). E domain III is an epitope for efficient neutralizing antibodies while the capsid protein contains T cell epitopes. Besides combining B and T cell epitopes, Tetra DIIIC is highly immunogenic due to its aggregate form and a two-component adjuvant. Following previous studies assessing the monovalent DIIIC formulations, we addressed here the quality and breadth of the T cell- and antibody response of Tetra DIIIC in mice. Tetra DIIIC induced a Th1-type response against all four DENV serotypes and dengue-specific antibodies were predominantly IgG1 and IgG2a and neutralizing, while the induction of neutralizing antibodies was dependent on IFN signaling. Importantly, the Th1 and IgG1/IgG2a profile of the DIIIC vaccine approach is similar to an efficient natural anti-dengue response.

Limited antigenic diversity of Plasmodium falciparum apical membrane antigen 1 supports the development of effective multi-allele vaccines

BACKGROUND

Polymorphism in antigens is a common mechanism for immune evasion used by many important pathogens, and presents major challenges in vaccine development. In malaria, many key immune targets and vaccine candidates show substantial polymorphism. However, knowledge on antigenic diversity of key antigens, the impact of polymorphism on potential vaccine escape, and how sequence polymorphism relates to antigenic differences is very limited, yet crucial for vaccine development. Plasmodium falciparum apical membrane antigen 1 (AMA1) is an important target of naturally-acquired antibodies in malaria immunity and a leading vaccine candidate. However, AMA1 has extensive allelic diversity with more than 60 polymorphic amino acid residues and more than 200 haplotypes in a single population. Therefore, AMA1 serves as an excellent model to assess antigenic diversity in malaria vaccine antigens and the feasibility of multi-allele vaccine approaches. While most previous research has focused on sequence diversity and antibody responses in laboratory animals, little has been done on the cross-reactivity of human antibodies.

METHODS

We aimed to determine the extent of antigenic diversity of AMA1, defined by reactivity with human antibodies, and to aid the identification of specific alleles for potential inclusion in a multi-allele vaccine. We developed an approach using a multiple-antigen-competition enzyme-linked immunosorbent assay (ELISA) to examine cross-reactivity of naturally-acquired antibodies in Papua New Guinea and Kenya, and related this to differences in AMA1 sequence.

RESULTS

We found that adults had greater cross-reactivity of antibodies than children, although the patterns of cross-reactivity to alleles were the same. Patterns of antibody cross-reactivity were very similar between populations (Papua New Guinea and Kenya), and over time. Further, our results show that antigenic diversity of AMA1 alleles is surprisingly restricted, despite extensive sequence polymorphism. Our findings suggest that a combination of three different alleles, if selected appropriately, may be sufficient to cover the majority of antigenic diversity in polymorphic AMA1 antigens. Antigenic properties were not strongly related to existing haplotype groupings based on sequence analysis.

CONCLUSIONS

Antigenic diversity of AMA1 is limited and a vaccine including a small number of alleles might be sufficient for coverage against naturally-circulating strains, supporting a multi-allele approach for developing polymorphic antigens as malaria vaccines.

Identification and characterization of a multispecific monoclonal antibody G2 against chicken prion protein

We previously generated a monoclonal antibody (mAb), G2, by immunizing mice with Residues 174-247 of the chicken prion protein (ChPrP(C) ). In this study, we found that G2 possessed an extremely unusual characteristic for a mAb; in particular, it could react with at least three proteins other than ChPrP(C) , the original antigenic protein. We immunoscreened a complementary DNA library from chicken brain DNA and found three proteins (SEPT3, ATP6V1C1, and C6H10orf76) that reacts with G2. There were no regions of amino acid sequence similarity between ChPrP(C) and SEPT3, ATP6V1C1, or C6H10orf76. We selected ATP6V1C1 as a representative of the three proteins and identified the epitope within ATP6V1C1 that reacts with G2. The amino acid sequence of the G2 epitope within ATP6V1C1 (Pep8) was not related to the G2 epitope within ChPrP(C) (Pep18mer). However, enzyme-linked immunosorbent assay, surface plasmon resonance (SPR), and isothermal titration calorimetry (ITC) experiments indicated that these two peptides have similar binding affinity for G2. The apparent KD values of Pep18mer and Pep8 obtained from SPR experiments were 2.9 × 10(-8) and 1.6 × 10(-8) M, respectively. Antibody inhibition test using each peptide indicated that the binding sites of the two different peptides overlapped each other. We observed that these two peptides substantially differed in several binding characteristics. Based on the SPR experiments, the association and dissociation rate constants of Pep18mer were higher than those of Pep8. A clear difference was also observed in ITC experiments. These differences may be explained by G2 adopting different binding conformations and undergoing different binding pathways.

A cryptic polyreactive antibody recognizes distinct clades of HIV-1 glycoprotein 120 by an identical binding mechanism

Polyreactive antibodies play an important role for neutralization of human immunodeficiency virus (HIV). In addition to intrinsic polyreactive antibodies, the immune system of healthy individuals contains antibodies with cryptic polyreactivity. These antibodies acquire promiscuous antigen binding potential post-translationally, after exposure to various redox-active substances such as reactive oxygen species, iron ions, and heme. Here, we characterized the interaction of a prototypic human antibody that acquires binding potential to glycoprotein (gp) 120 after exposure to heme. The kinetic and thermodynamic analyses of interaction of the polyreactive antibody with distinct clades of gp120 demonstrated that the antigen-binding promiscuity of the antibody compensates for the molecular heterogeneity of the target antigen. Thus, the polyreactive antibody recognized divergent gp120 clades with similar values of the binding kinetics and quantitatively identical changes in the activation thermodynamic parameters. Moreover, this antibody utilized the same type of noncovalent forces for formation of complexes with gp120. In contrast, HIV-1-neutralizing antibodies isolated from HIV-1-infected individuals, F425 B4a1 and b12, demonstrated different binding behavior upon interaction with distinct variants of gp120. This study contributes to a better understanding of the physiological role and binding mechanism of antibodies with cryptic polyreactivity. Moreover, this study might be of relevance for understanding the basic aspects of HIV-1 interaction with human antibodies.

Insights into B cells and HIV-specific B-cell responses in HIV-infected individuals

Human immunodeficiency virus (HIV) disease is associated with dysregulation and dysfunction involving all major lymphocyte populations, including B cells. Such perturbations occur early in the course of infection and are driven in large part by immune activation resulting from ongoing HIV replication leading to bystander effects on B cells. While most of the knowledge regarding immune cell abnormalities in HIV-infected individuals has been gained from studies conducted on the peripheral blood, it is clear that the virus is most active and most damaging in lymphoid tissues. Here, we discuss B-cell perturbations in HIV-infected individuals, focusing on the skewing of B-cell subsets that circulate in the peripheral blood and their counterparts that reside in lymphoid tissues. This review also highlights recent advances in evaluating HIV-specific B-cell responses both in the memory B-cell compartment, as well as in circulating antibody-secreting plasmablasts and the more differentiated plasma cells residing in tissues. Finally, we consider how knowledge gained by investigating B cells in HIV-infected individuals may help inform the development of an effective antibody-based HIV vaccine.

Antibody polyreactivity in health and disease: statu variabilis

An Ab molecule or a BCR that is able to bind multiple structurally unrelated Ags is defined as polyreactive. Polyreactive Abs and BCRs constitute an important part of immune repertoires under physiological conditions and may play essential roles in immune defense and in the maintenance of immune homeostasis. In this review, we integrate and discuss different findings that reveal the indispensable role of Ag-binding polyreactivity in the immune system. First, we describe the functional and molecular characteristics of polyreactive Abs. The following part of the review concentrates on the biological roles attributed to polyreactive Abs and to polyreactive BCRs. Finally, we discuss recent studies that link Ig polyreactivity with distinct pathological conditions.