Engaging the ‘A’ Class Antibody: Variable-Heavy (VH) region influencing IgA1&2 engagement of FcαRI and superantigen proteins G, A, and L

Interest in IgA as an alternative therapeutic and diagnostic antibody has increased over the years, yet much remains to be investigated especially given their importance in activating immune cells in blood and in mucosal immunity. Recent whole antibody-based investigations have shown significant distal effects between the variable (V) and constant (C)-regions that can be mitigated by the different hinge regions of the human IgA subtypes A1 and A2. Diving deeper into the mechanisms underlying this, systematic VH manipulations retaining the CDRs were performed on a panel of 28 IgA1s and A2s across the Trastuzumab and Pertuzumab models, revealed distal effects on FcαRI binding. Further insights from structural modelling showed these effects to also be mitigated by the differing glycosylation patterns in IgA1 and 2 to explain reversal of trends of IgA1s and 2s effected by slight changes in the CDRs. IgAs bound at the Fc showed similar trends but magnitudes better binding to Her2 with that bound by ppL, showing that ppL can sterically hinder Her2 antigen binding. Contrary to canonical knowledge, we found strong evidence of IgAs binding SpG that was narrowed to be at the CH2-3 region, and that the likely binding with SpA was beyond VH3 FWR and most likely at the CH1. VH1 was found to be the most suitable framework (FWRs) for CDR-grafting for both IgA1 and 2. With relevance to interactions with the microbiome at mucosal surfaces, mechanistic insight of how these IgAs can interact bacterial superantigens proteins G, A, and L are also discovered for potential future interventions.One Sentence SummaryAn insight into the mechanism of distal V-region effects on FCAR and superantigens proteins G, A, and L by both IgA1 and A2.

An insertion unique to SARS-CoV-2 exhibits superantigenic character strengthened by recent mutations

Multisystem Inflammatory Syndrome in Children (MIS-C) associated with Coronavirus Disease 2019 (COVID-19) is a newly recognized condition in which children with recent SARS-CoV-2 infection present with a constellation of symptoms including hypotension, multiorgan involvement, and elevated inflammatory markers. These symptoms and the associated laboratory values strongly resemble toxic shock syndrome, an escalation of the cytotoxic adaptive immune response triggered upon the binding of pathogenic superantigens to MHCII molecules and T cell receptors (TCRs). Here, we used structure-based computational models to demonstrate that the SARS-CoV-2 spike (S) exhibits a high-affinity motif for binding TCR, interacting closely with both the α- and β-chains variable domains’ complementarity-determining regions. The binding epitope on S harbors a sequence motif unique to SARS-CoV-2 (not present in any other SARS coronavirus), which is highly similar in both sequence and structure to bacterial superantigens. Further examination revealed that this interaction between the virus and human T cells is strengthened in the context of a recently reported rare mutation (D839Y/N/E) from a European strain of SARS-CoV-2. Furthermore, the interfacial region includes selected residues from a motif shared between the SARS viruses from the 2003 and 2019 pandemics, which has intracellular adhesion molecule (ICAM)-like character. These data suggest that the SARS-CoV-2 S may act as a superantigen to drive the development of MIS-C as well as cytokine storm in adult COVID-19 patients, with important implications for the development of therapeutic approaches.SignificanceAlthough children have been largely spared from severe COVID-19 disease, a rare hyperinflammatory syndrome has been described in Europe and the East Coast of the United States, termed Multisystem Inflammatory Syndrome in Children (MISC). The symptoms and diagnostic lab values of MIS-C resemble those of toxic shock, typically caused by pathogenic superantigens stimulating excessive activation of the adaptive immune system. We show that SARS-CoV-2 spike has a sequence and structure motif highly similar to those of bacterial superantigens, and may directly bind to the T cell receptors. This sequence motif, not present in other coronaviruses, may explain the unique potential for SARS-CoV-2 to cause both MIS-C and the cytokine storm observed in adult COVID-19 patients.

Protein A superantigen: structure, engineering and molecular basis of antibody recognition

Staphylococcus aureus interacts with the human immune system through the production of secreted factors. Key among these is protein A, a B-cell superantigen capable of interacting with both antibody Fc and VH regions. Here, we review structural and molecular features of this important example of naturally occurring bacterial superantigens, as well as engineered variants and their application in biotechnology.

Western Faculty Profile: Dr. John McCormick

Dr. McCormick is an Associate Professor in the Department of Microbiology and Immunology and a Scientist at the Lawson Health Research Institute. His research is in bacteriology, with a primary focus on bacterial toxins called “superantigens”. His research interests are in the molecular biology and evolution of bacterial superantigens inStaphylococcus aureus and Streptococcus pyogenes, the role of superantigens in toxic shock syndrome, and the engineering of superantigens as targeted anti-cancer immunotherapeutics. Dr. McCormick teaches an undergraduate course in microbiology in addition to supervising undergraduate and graduate students. Alex Zhou, reviewer on the WURJHNS Editorial Board, interviewed Dr. McCormick to learn more about his ongoing research, motivations, career path to Western and advice for students.