Comparison of a single-antigen microimmunofluorescence assay and inclusion fluorescent-antibody assay for detecting chlamydial antibodies and correlation of the results with neutralizing ability

Abstract

An inclusion fluorescent-antibody assay (IFA) with McCoy cells infected with Chlamydia trachomatis serovar L2 was compared with a single-antigen (L2) microimmunofluorescence (MIF) assay for the detection of antichalmydial antibodies. A total of 562 serum specimens were tested by both assays, and sera representing a range of titers were tested for their ability to neutralize the infectivity of C. trachomatis. Overall, there was poor correlation between the two assays (r2 = 0.62). With most sera the inclusion IFA was more sensitive. There was better correlation between IFA titer and ability to neutralize the five serovars tested (L2, L3, C, E, and F) than between the MIF assay and neutralization. In summary, the IFA appeared to be more sensitive than the MIF assay for detecting antibodies to C. trachomatis.