Separation and partial characterization of a type-specific antigen from Chlamydia trachomatis.

Type-specific antigens of Chlamydia trachomatis have been demonstrated by the mouse toxicity prevention test and a variety of immunofluorescent techniques. In addition, biologic activity has been associated with these antigens in terms of type-specific immunity to trachoma infections. This report is the first to describe the detection of a soluble type-specific antigen of C. trachomatis and its separation from those antigens that cross-react among different immunotypes. Test antigens were prepared by labeling the surface components of purified, yolk sac grown organisms with a radioiodinated intermediate (Bolton-Hunter reagent, 125I). The organisms were solubilized with Triton X-100 and gel filtered through Sepharose 6B. All fractions were then tested in radioimmunoassay for binding with rabbit antisera raised against solubilized immunogens prepared from homologous and heterologous strain organisms propagated in BHK-21 cells. A fraction demonstrating homologous binding only was used in subsequent modified procedures for the preparation of quantities of type-specific antigen sufficient for analysis. The antigen appears to be a heat labile, cell surface protein associated with apparent immunogenic activity during the course of actual chlamydial eye infection.