Evidence that a significant number of naive T cells enter non‐lymphoid organs as part of a normal migratory pathway

Only activated and effector memory T cells are thought to access non‐lymphoid tissues. In contrast, naive T cells are thought to circulate only between the blood, lymph and secondary lymphoid organs. We examined the phenotype of endogenous T cells in various non‐lymphoid organs and showed that a subset of cells exhibited an apparently naive phenotype and were functionally inactive. FTY720 treatment selectively depleted this population from the non‐lymphoid tissues. In addition, RAG‐deficient TCR transgenic CD4 and CD8 T cells were present in non‐lymphoid tissues in bone marrow chimeric mice and in situ imaging analysis revealed their location in the parenchymal tissues. Moreover, migration of TCR transgenic T cells to non‐lymphoid tissues after adoptive transfer was pertussis‐toxin resistant. Overall, the results suggest that naive T cells may circulate through non‐lymphoid tissues as part of their normal migratory pathway.