APC antigen-presenting cell IDO indoleamine 2,3-dioxygenase IFN-γ interferon-γ MHC major histocompatibility complex MOMP major outer-membrane protein NO nitric oxide

Chlamydia trachomatis is the most common cause of bacterial sexually transmitted disease in the United States, as well as the leading cause of preventable blindness worldwide. Immunity to C. trachomatis requires a variety of cell types, each employing an array of effector functions. Recent work has demonstrated that both CD4+ and CD8+ T lymphocytes play a major role in protective immunity to C. trachomatis, predominantly through their secretion of interferon-γ. This review describes the generation of acquired immunity to C. trachomatis and focuses on how T cells contribute to both protection and immunopathology.