Thymic origin of intestinal αβ T cells revealed by fate mapping of RORγ[t.sup.+] cells

Intestinal intraepithelial T lymphocytes (IELs) are likely to play a key role in host mucosal immunity and, unlike other T cells, have been proposed to differentiate from local precursors rather than from thymocytes. We show here that IELs expressing the αβ T cell receptor are derived from precursors that express RORγt, an orphan nuclear hormone receptor detected only in immature [CD4].sup.+][CD8.sup.+] thymocytes, fetal lymphoid tissue--inducer (LTi) cells, and LTi-like cells in cryptopatches within the adult intestinal lamina propria. Using cell fate mapping, we found that all intestinal αβ T cells are progeny of [CD4.sup.+][CD8.sup.+] thymocytes, indicating that the adult intestine is not a significant site for αβ T cell development. Our results suggest that intestinal RORγ[t.sup.+] cells are local organizers of mucosal lymphoid tissue.
The gut-associated immune system includes mesenteric lymph nodes (mLNs), Peyer's patches (PPs), and T lymphocytes that reside in the intestinal lamina propria (LPLs) and within the single layer of intestinal [...]