Protective immunity against mouse upper genital tract pathology correlates with high IFNγ but low IL-17 T cell and anti-secretion protein antibody responses induced by replicating chlamydial organisms in the airway.

To search for optimal immunization conditions for inducing protective immunity against upper genital tract pathologies caused by chlamydial intravaginal infection, we compared protection efficacy in mice immunized intranasally or intramuscularly with live or inactivated Chlamydia muridarum organisms. Mice immunized intranasally with live organisms developed strong protection against both vaginal shedding of infectious organisms and upper genital tract pathologies. The protection correlated with a robust antigen-specific T cell response with high IFNγ but low IL-17. Although a significant level of IL-5 was also detected, these mice maintained an overall Th1-dorminant immunity following immunization and challenge infection. On the contrary, mice immunized intranasally with inactivated organisms or intramuscularly with live or inactivated organisms produced high levels of IL-17 and still developed significant upper genital tract pathologies. High titers of antibodies against chlamydial secretion antigens were detected only in mice immunized intranasally with live organisms but not mice in other groups, suggesting that the intranasally inoculated live organisms were able to undergo replication and immune responses to the chlamydial secretion proteins may contribute to protective immunity. These observations have provided important information on how to develop subunit vaccines for inducing protective immunity against urogenital infection with Chlamydia trachomatis organisms.