Reticulate bodies as single antigen in Chlamydia trachomatis serology with microimmunofluorescence

Formalin-fixed, purified reticulate bodies (RB) of Chlamydia trachomatis immunotype C/TW-3/OT were used as a serological test antigen in the microimmunofluorescence test. The sensitivity and specificity of the RB antigen were compared to elementary bodies (EB) used as antigens in the detection of C. trachomatis antibodies in human sera by microimmunofluorescence. RB reacted with all known C. trachomatis immunotypes with the same sensitivity as the homotypic EB. In routine serology with sera and endocervical secretions, the RB antigen had a sensitivity similar to that of the EB in detecting serum antibodies, endocervical secretion antibodies, and antibodies of immunoglobulin M and G classes. No false-positive reactions were detected with control sera. All positive reactions showed type-specific antibodies against an EB immunotype. RB seemed to demonstrate chlamydial group reactivity; sera from 10 psittacosis patients diagnosed clinically and serologically by complement fixation showed five positive, three equivocal, and two negative reactions. By immunofluorescence, RB appeared as distinct rings demonstrating uniform peripheral surface fluorescence at their rims. The EB appeared as pinpoint-sized dots. C/TW-3/OT RB used as a single test anitgen should provide a simple and sensitive serological assay for the detection of C. trachomatis antibody.