Antibodies against Chlamydia measured by an ELISA method.

An enzyme-linked immunosorbent assay (ELISA) for the detection of serum IgG and IgM antibodies against chlamydia group antigen is presented. 187 selected sera were tested both in the ELISA and in the complement-fixation test (CFT). Of 71 sera with negative results in the CFT, 19 (26.8%) were positive in the ELISA. Of 116 CFT positive sera, ten (8,6%) were ELISA negative. In 35 of 72 sera (48.6%) with CFT titre less than 40 chlamydial IgM was demonstrated, while 11 of 115 sera (9.5%) with CFT titre less than 40, were IgM positive. IgM may inhibit binding of IgG to the antigen by competition. The ELISA showed a greater discrimination between titre-values compared to the CFT. The results are presented as "estimated titers". This method is based on linear logarithmic dose-response curves. The method gives a continuous titre scale, is easily understood, is reproducible and may be used in seroepidemiology. One single serum dilution is required except for sera with high titre which have to be retested at a higher dilution.