Antigen density in ELISA; effect on avidity dependency.

Two different densities of an antigen (bovine serum albumin, BSA) were used on paper disks is an enzyme-linked immunosorbent assay (ELISA) for chicken IgG anti-BSA antibodies. Disks of different antigen density but containing the same amount of the antigen showed a difference in immunoreactivity. Samples containing large amounts of low avidity antibodies gave higher absorbance when disks of lower antigen density were used. This phenomenon was not due to a competition between antibodies of various immunoglobulin classes. These findings may indicate that antigen density affects the sensitivity of ELISA to antibodies of various avidities.