Long-lived colitogenic CD4+ memory T cells residing outside the intestine participate in the perpetuation of chronic colitis.

To understand the perpetuation of inflammatory bowel disease (IBD), it is important to clarify whether the colitogenic CD4(+) T cells are self-limited effector or long-lived memory T cells. We here investigate the latency of colitogenic CD4(+) T cells in the remission stage of colitis under germfree (GF) conditions. We isolated splenic (SP) CD4(+) T cells from colitic CD4(+)CD45RB(high) T cell-injected SCID mice maintained under specific pathogen-free (SPF) conditions and transferred them into SPF or GF SCID mice. Donor colitic SP CD4(+) T cells have a characteristic CD44(high)CD62L(-)IL-7Ralpha(high) effector-memory T-type phenotype. Six weeks after transfer of cells to GF SCID mice, one group of mice was continued in GF conditions (GF-->GF), and the other was transferred into SPF conditions (GF-->SPF). GF-->SPF but not GF-->GF SCID mice developed colitis with elevated production of Th1 and Th17 cytokines at 4 wk after transfer. Surprisingly, a large number of CD4(+) effector-memory T cells and a small but substantial number of central-memory T cells remained resident in SP and bone marrow, but not in lamina propria, of the GF-->GF SCID recipients. Consistent with this, GF-->SPF but not GF-->GF SCID mice rapidly developed colitis. Taken together, these findings suggest that long-lived colitogenic memory CD4(+) cells can be established even in the presence of commensal Ags, reside outside the intestine in the absence of commensal bacteria, and participate in the perpetuation of colitis. Thus, blocking a stimulus of colitogenic memory CD4(+) cells such as IL-7 may have therapeutic benefit for treatment of inflammatory bowel disease.