T-helper 17 and Interleukin-17-Producing Lymphoid Tissue Inducer-Like Cells Make Different Contributions to Colitis in Mice

BACKGROUND & AIMS: T helper (Th) 17 cells that express the retinoid-related orphan receptor (ROR) gamma t contribute to the development of colitis in mice, yet are found in normal and inflamed intestine. We investigated their development and functions in intestines of mice. METHODS: We analyzed intestinal Th17 cells in healthy and inflamed intestinal tissues of mice. We analyzed expression of lymphotoxin (LT)alpha by Th17 cells and lymphoid tissue inducer-like cells. RESULTS: LT alpha(-/-) and ROR gamma t(-/-) mice had significantly lower percentages of naturally occurring Th17 cells in the small intestine than wild-type mice. Numbers of CD3(-)CD4(+/-) interleukin-7R alpha(+) c-kit(+) CCR6(+) NKp46(-) lymphoid tissue inducer-like cells that produce interleukin-17A were increased in LT alpha(-/-) and LT alpha(-/-) X recombination activating gene (RAG)-2(-/-) mice, compared with wild-type mice, but were absent from ROR gamma t(-/-) mice. Parabiosis of wild-type and LT alpha(-/-) mice and bone marrow transplant experiments revealed that LT alpha-dependent gut-associated lymphoid tissue structures are required for generation of naturally occurring Th17 cells. However, when wild-type or LT alpha(-/-) CD4(+)CD45RB(high) T cells were transferred to RAG-2(-/-) or LT alpha(-/-) X RAG-2(-/-) mice, all groups, irrespective of the presence or absence of LT alpha on the donor or recipient cells, developed colitis and generated Th1, Th17, and Th17/Th1 cells. RAG-2(-/-) mice that received a second round of transplantation, with colitogenic but not naturally occurring Th17 cells, developed intestinal inflammation. The presence of naturally occurring Th17 cells in the colons of mice inhibited development of colitis after transfer of CD4(+)CD45RB(high) T cells and increased the numbers of Foxp3(+) cells derived from CD4(+)CD45RB(high) T cells. CONCLUSIONS: Gut-associated lymphoid tissue structures are required to generate naturally occurring Th17 cells that have regulatory activities in normal intestines of mice, but not for colitogenic Th17 and Th17/Th1 cells during inflammation.