IFNγ-producing iNKTs restrict a live-attenuated chlamydia oral vaccine in the large intestine.

Chlamydia muridarum continuously sheds live organisms and persists in the large intestine following intracolonic inoculation, while the live-attenuated chlamydia oral vaccine intrOv, an IFNγ-susceptible mutant of C. muridarum, fails to do so. IFNγ delivered by group 3 innate lymphoid cells (ILC3s) have been shown to block intrOv shedding. We now report that mice deficient in lymphocytes but competent in ILCs allowed intrOv to persist, revealing a critical role of lymphocytes for preventing intrOv persistence. The responsible lymphocyte subsets are natural killer T cells (NKTs), as mice deficient in either CD1d or β2m permitted intrOv to persist. We further narrowed the responsible cells to invariant NKTs (iNKTs) that produce IFNγ, as mice deficient in TCRα J18 segment (Traj18), T-bet, or IFNγ failed to prevent intrOv persistence. Consistently, intrOv induced IFNγ+iNKTs, and wild-type iNKTs prevented intrOv persistence in mice deficient in either lymphocytes or IFNγ. Thus, IFNγ+iNKTs are both necessary and sufficient for preventing intrOv persistence, while IFNγ+ILC3s are for blocking intrOv shedding, revealing a division of labor between IFNγ+iNKTs and IFNγ+ILC3s in regulating the interaction of the obligate intracellular Chlamydia with host mucosal tissue. The information is also essential for improving the safety and efficacy of intrOv as an oral vaccine.