Gastrointestinal Chlamydia-induced CD8⁺ T cells promote Chlamydial Pathogenicity in the female upper genital tract

Chlamydia is known to both ascend to the upper genital tract and spread to the gastrointestinal tract following intravaginal inoculation. Gastrointestinal Chlamydia was recently reported to promote chlamydial pathogenicity in the genital tract since mice intravaginally inoculated with an attenuated Chlamydia strain, which alone failed to develop pathology in the genital tract, were restored to develop hydrosalpinx by intragastric coinoculation with wild-type Chlamydia. Gastrointestinal Chlamydia promoted hydrosalpinx via an indirect mechanism since Chlamydia in the gut did not directly spread to the genital tract lumen. In the current study, we further investigated the role of CD8⁺ T cells in the promotion of hydrosalpinx by gastrointestinal Chlamydia. First, we confirmed that intragastric coinoculation with wild-type Chlamydia promoted hydrosalpinx in mice that were inoculated with an attenuated Chlamydia strain in the genital tract 1 week earlier. Second, the promotion of hydrosalpinx by intragastrically coinoculated Chlamydia was blocked by depleting CD8⁺ T cells. Third, adoptive transfer of gastrointestinal Chlamydia-induced CD8⁺ T cells was sufficient for promoting hydrosalpinx in mice that were intravaginally inoculated with an attenuated Chlamydia strain. These observations have demonstrated that CD8⁺ T cells induced by gastrointestinal Chlamydia are both necessary and sufficient for promoting hydrosalpinx in the genital tract. The study has laid a foundation for further revealing the mechanisms by which Chlamydia-induced T lymphocyte responses (as a 2nd hit) promote hydrosalpinx in mice with genital Chlamydia-triggered tubal injury (as a 1st hit), a continuing effort in testing the two-hit hypothesis as a chlamydial pathogenic mechanism.