Enzyme-Linked Immunosorbent Assay (ELISA) serum IgA/IgG/IgM & subclasses

The ELISA assay is a serological method used to detect and quantify antigen‑specific antibodies directed against viral or bacterial proteins. In this assay, the target antigen is immobilized on a 96‑well microtiter plate. Serially diluted serum samples are added, allowing antigen‑specific IgG antibodies, if present, to bind to the coated antigen. After incubation and washing steps, an enzyme‑conjugated secondary antibody (e.g., horseradish peroxidase, HRP) specific for human IgG is added to detect bound antibodies. Following addition of a suitable substrate, a colorimetric reaction proportional to the amount of antigen‑specific IgG is generated and measured as optical density (OD) using a spectrophotometer. OD values provide a quantitative, semi‑quantitative, or qualitative assessment of IgG antibody levels. This assay is widely used for sero‑epidemiological studies, vaccine immunogenicity assessments, and monitoring of immune responses following infection or vaccination.