Identification of Chlamydia trachomatis antigens recognized by human CD4+ T lymphocytes by screening an expression library.

Identification of the immunogenic proteins that induce Chlamydia trachomatis (CT)-specific T cell responses is crucial to the development of protective vaccines and understanding the mechanisms of chlamydia-induced pathology. To characterize the targets of the human T cell response we have used chlamydia-reactive human T cell clones as cellular probes to screen a CT genomic library expressed in Escherichia coli using peripheral blood mononuclear cells to present antigens. The library was screened with three chlamydia-reactive T cell clones of unknown specificity and three novel stimulatory chlamydia antigens were identified. These E. coli recombinants were shown to express the chlamydia proteins, enolase, pmpD and CT579. Enolase and pmpD proteins were purified and shown to induce the proliferation of synovial fluid mononuclear cells isolated from the knee joints of patients suffering from chlamydia-associated reactive arthritis. We suggest that these stimulatory antigens are common targets of the T cell response in this group of patients. A greater understanding of T cell-mediated immunity in uncomplicated CT infection, and in patients with CT-induced chronic inflammatory disease (trachoma, salpingitis, arthritis) may identify the principal immune responses associated with immunopathology.