Regulation of chlamydial spreading from the small intestine to the large intestine by IL-22-producing CD4⁺ T cells

Following an oral inoculation, Chlamydia muridarum descends to the mouse large intestine for long-lasting colonization. However, a mutant C. muridarum that lacks the plasmid-encoded protein pGP3 due to an engineered premature stop codon (designated as CMpGP3S) failed to do so even following an intrajejunal inoculation. This was because a CD4⁺ T cell-dependent immunity prevented the spread of CMpGP3S from the small intestine to the large intestine. In the current study, we found that mice deficient in IL-22 (IL-22^−/−) allowed CMpGP3S to spread from the small intestine to the large intestine on day 3 after intrajejunal inoculation, indicating a critical role of IL-22 in regulating the chlamydial spread. The responsible IL-22 is produced by CD4⁺ T cells since IL-22^−/− mice were rescued to block the CMpGP3S spread by donor CD4⁺ T cells from C57BL/6J mice. Consistently, CD4⁺ T cells lacking IL-22 failed to block the spread of CMpGP3S in Rag2^−/− mice, while IL-22-competent CD4⁺ T cells did block. Furthermore, mice deficient in cathelicidin-related antimicrobial peptide (CRAMP) permitted the CMpGP3S spread, but donor CD4⁺ T cells from CRAMP^−/− mice were still sufficient for preventing the CMpGP3S spread in Rag2^−/− mice, indicating a critical role of CRAMP in regulating chlamydial spreading, and the responsible CRAMP is not produced by CD4⁺ T cells. Thus, the IL-22-producing CD4⁺ T cell-dependent regulation of chlamydial spreading correlated with CRAMP produced by non-CD4⁺ T cells. These findings provide a platform for further characterizing the subset(s) of CD4⁺ T cells responsible for regulating bacterial spreading in the intestine.