Practice question

Detection of HIV infection relies on measuring patient IgG against viral antigens such as p24, gp120 and gp41. In indirect format, recombinant HIV proteins are immobilized on solid phase, then incubated with serum. If anti-HIV antibodies are present, they bind specifically to coated antigens. Enzyme-linked anti-human IgG secondary antibody amplifies signal upon substrate addition. Direct coating of antibody would detect antigen, not suitable for early serology. Sandwich assay requires antigen with two epitopes and is designed for antigen detection, not circulating antibodies. Hence indirect design provides sensitivity and specificity for seroprevalence screening.