Relation between avidity and specificity of monoclonal anti-chlamydial antibodies in culture supernatants and ascitic fluids determined by enzyme immunoassay.

The relation between avidity and specificity of monoclonal antibodies to Chlamydia trachomatis elementary body antigens was studied by enzyme immunoassay. Avidity was estimated by performing the assay in 6 sample dilutions and using a curve-fitting procedure to extrapolate antibody binding in the presence of large antibody excess. Specificity was judged by the difference between end-point titers against homologous and heterologous antigens. By this method antibodies are divided into 2 groups, high specificity (Hs) and low specificity (Ls). Usually, antibodies from ascitic fluids belonged to the Ls group. However, the Ls group also included a few antibodies in supernatants. There was an inverse relationship between avidity and specificity in the Ls group. Immunoglobulin M (IgM) and IgG antibodies of the Hs group had different relative avidities. Avid IgM antibodies from ascitic fluid are not necessarily highly specific.