Role of cytokines in Chlamydia trachomatis protective immunity and immunopathy

Diseases caused by Chlamydia trachomatis infection and its sequelae represent major public health concerns worldwide. In order to rationally develop an effective vaccine to chlamydial infection, we need a better understanding of the mechanisms underlying the protective and pathological immune responses to chlamydial antigens. Recent studies in chlamydial immunobiology have demonstrated a close link between cytokine production patterns and the type of immune responses to this pathogen. In particular, IL-10 has been found to be associated with susceptibility to chlamydial infection and the typical pathological changes caused by the infection such as granuloma formation and fibrosis. Although Th1 type delayed hypersensitivity (DTH) is associated with protective immunity, the Th2 type DTH documented in interferon (IFN)-gamma gene knockout (KO) mice fails to control chlamydial infection. The Th2 type DTH is characterized by eosinophil and neutrophil infiltration and is associated with high levels of IL-4 and IL-5 production. The capability of dendritic cell (DC) in initiating T cell response to Chlamydia has been shown in studies using cultured DCs and a DC line. Further studies should be performed to elucidate the role played by DCs in natural chlamydial infection and the potential involvement of DC subsets in directing immune responses to chlamydial infection.