Enzyme-Linked Immunosorbent Assay (ELISA) Secretory IgA (S-IgA) / Total IgA

The ELISA assay for Secretory IgA (S‑IgA) and Total IgA is a sensitive immunological method designed to quantify mucosal and systemic antibody responses, providing key insights into first-line immune defense mechanisms. In this assay, specific antigens or capture antibodies are immobilized onto a 96‑well microtiter plate to selectively bind IgA antibodies present in biological samples such as serum, saliva, or mucosal fluids. Following incubation and washing steps, an enzyme-conjugated secondary antibody targeting human IgA is added to detect bound antibodies. For S‑IgA measurement, assays are specifically configured to capture the secretory component associated with mucosal IgA, enabling differentiation from serum IgA. Upon addition of a chromogenic substrate, a colorimetric reaction develops proportionally to the IgA concentration and is quantified as optical density (OD) using a spectrophotometer. The resulting OD values allow quantitative or semi‑quantitative evaluation of IgA levels, supporting the assessment of mucosal immunity, host-pathogen interactions, and immune responses induced by infection or vaccination. This assay is particularly valuable in studies of respiratory and gastrointestinal immunity, where S‑IgA plays a critical protective role.