Structural Adaptability of IgA and IgM Supports Broad SARS-CoV-2 Variant Neutralization

Area of Science:

• Immunology
• Virology
• Structural Biology

Background:

• Emerging SARS-CoV-2 variants present challenges for antibody neutralization.
• Antibody effectiveness depends on epitope mutations and antigenic presentation.

Purpose of the Study:

• To compare the neutralization capacity of IgG, IgA, and IgM isotypes of an anti-RBD antibody (8A5) against 18 SARS-CoV-2 variants.
• To investigate the structural and spatial factors influencing differential antibody efficacy.

Main Methods:

• Assessed neutralization of 18 SARS-CoV-2 variants using IgG, IgA, and IgM isotypes of the 8A5 antibody.
• Performed mutation analysis to identify key residues affecting antibody binding.
• Utilized negative-stain electron microscopy to visualize virion spike distribution.
• Conducted ELISA assays under varying antigen densities to assess antibody binding.

Main Results:

• Identified three neutralization classes: susceptible to all isotypes, resistant to IgG but sensitive to IgA/IgM, and resistant to all isotypes.
• Specific mutations (S371L-S373P-S375F) disrupted IgG binding more than IgA/IgM.
• L371F mutation abolished all antibody interactions.
• IgG binding decreased significantly at low antigen density, while IgA and IgM maintained binding due to their structure and multivalency.
• Spatial adaptability and geometric factors contribute to differential neutralization efficacy.

Conclusions:

• IgA and IgM isotypes demonstrate potential advantages over IgG in neutralizing SARS-CoV-2 variants, particularly those with altered antigen presentation or sparse epitopes.
• The findings support the rational design of IgA- and IgM-based antibody therapeutics for combating current and future viral threats.