CAPTURE-ELISA - A NEW ASSAY FOR THE DETECTION OF IMMUNOGLOBULIN-M ISOTYPE ANTIBODIES USING CHLAMYDIA-TRACHOMATIS ANTIGEN

We present here a new method of IgM antibody-capture enzyme-linked imm unosorbent assay (IgM-Capture-ELISA) for the diagnosis of recently acq uired infections with Chlamydia trachomatis. For this analysis, plates were coated with goat IgG anti-human Fc mu. The capture of serum IgM antibodies was revealed indirectly by the sequential addition of bioti nylated chlamydial proteins and peroxidase-conjugated streptavidin. In chlamydial extracts, cysteine-rich proteins are preferential antigeni c targets for the humoral response. 3-(N-maleimidopropionyl)-biocytin (MPB), which binds biotinylated moieties to sulfhydryl groups, was use d for the labeling procedure. The preservation of the antigenic specif icity of labeled proteins was controlled by a blotting of these protei ns, which were, respectively, probed either with specific IgM antibodi es or with streptavidin. This analysis revealed that, after labeling, recognized epitopes are more particularly present on the major outer m embrane protein (MOMP) of Chlamydia trachomatis. The validation of IgM -Capture-ELISA was assessed by using 170 selected sera from patients s uspected of being infected by Chlamydia. Results were respectively com pared to conventional indirect immunofluorescence assays (MIF-IgM assa ys) and to Western blotting. Sixteen sera were found to possess IgM an tibodies against Chlamydia trachomatis with IgM-Capture-ELISA. Among t hese 16 sera, 14 and 15 were, respectively, positive with MIF-IgM assa ys and in Western blotting. Data obtained with IgM-Capture-ELISA revea l the absence of false-positive results in sera containing rheumatoid factor, which has been shown to interfere in the two other methods. Ig M-Capture-ELISA value was then confirmed using sera from patients cons ulting for genital or pulmonary diseases, from patients with confirmed chlamydial infections, and from patients with other pathologies. IgM- Capture-ELISA appears as an alternative simple semi-quantitative assay for the detection of early chlamydial infection.