Pathogenic and Protective Roles of Neutrophils in Chlamydia trachomatis Infection

Chlamydia trachomatis (Ct) is an obligate intracellular pathogen that causes the most commonly diagnosed bacterial sexually transmitted infection (STI) and is a leading cause of preventable blindness globally. Ct infections can generate a strong pro-inflammatory immune response, leading to immune-mediated pathology in infected tissues. Neutrophils play an important role in mediating both pathology and protection during infection. Excessive neutrophil activation, migration, and survival are associated with host tissue damage during Chlamydia infections. In contrast, neutrophils also perform phagocytic killing of Chlamydia in the presence of IFN-γ and anti-Chlamydia antibodies. Neutrophil extracellular traps (NETs) and many neutrophil degranulation products have also demonstrated strong anti-Chlamydia functions. To counteract this neutrophil-mediated protection, Chlamydia has developed several evasion strategies. Various Chlamydia proteins can limit potentially protective neutrophil responses by directly targeting receptors present on the surface of neutrophils or neutrophil degranulation products. In this review, we provide a survey of current knowledge regarding the role of neutrophils in pathogenesis and protection, including the ways that Chlamydia circumvents neutrophil functions, and we propose critical areas for future research.