Validation of a Mucosal IgA Assay for SARS-CoV-2

Mucosal immunity, including antibodies like immunoglobulin A (IgA), function as the body’s first line of defense in the respiratory tract, particularly against viruses. An anti-rS protein IgA enzyme-linked immunosorbent assay (ELISA) was developed using the Omicron XBB.1.5 subvariant of SARS-CoV-2 and was validated to demonstrate the suitability of the method for testing saliva from SARS-CoV-2 vaccine clinical trials. This assay successfully met acceptance criteria for inter-/intra-assay precision, specificity, selectivity, linearity, lower/upper limits of quantitation, and assay robustness. The IgA in saliva was stable for up to 7 freeze/thaw cycles, for up to 48 h at 24 °C, up to 7 days at 4 °C, up to 3 weeks at −20 °C, and up to 1 year at −80 °C. After validation using Omicron XBB.1.5 rS protein, cross-reactivity was demonstrated with the SARS-CoV-2 variant JN.1. This validated IgA assay can be a valuable tool to assess mucosal IgA levels in SARS-CoV-2 clinical trials.