Role of LFA-1 in the activation and trafficking of T cells: Implications in the induction of chronic colitis

Introduction: We have previously demonstrated that adoptive transfer of naïve CD4⁺ T cells devoid of lymphocyte function-associated antigen-1-deficient (LFA-1; CD11a/CD18) into recombination activating gene-1 (RAG-1) deficient (RAG^-/-) mice fails to induce chronic colitis whereas transfer of wild type (WT) T-cells induces unrelenting and chronic disease. Methods: The objectives of this study were to assess the role of lymphocyte function-associated antigen-1 (LFA-1) in enteric antigen (EAg)-induced activation of T cells in vitro and in vivo and to define the importance of this integrin in promoting trafficking of T cells to the mesenteric lymph nodes (MLNs) and colon. Results: We found that EAg-pulsed dendritic cells (DCs) induced proliferation of LFA-1-deficient (CD11a ^-/-) CD4⁺ T cells that was very similar to that induced using WT T cells, suggesting that LFA-1 is not required for activation/ proliferation of T cells in vitro. Coculture of WT or CD11a^-/- T cells with EAg-pulsed DCs induced the generation of similar amounts of interferon-gamma, interleukin (IL)-4, and IL-10, whereas IL-17A production was reduced ≈2-fold in cocultures with CD11a^-/- T cells. Short-term (20-22 hours) trafficking studies demonstrated that while both WT and CD11a ^-/- T cells migrated equally well into the spleen, liver, lungs, small intestine, cecum, and colon, trafficking of CD11a^-/- T cells to the MLNs was reduced by 50% when compared to WT T cells. When the observation period was extended to 3-7 days posttransfer, we observed ≈2-3-fold more WT T cells within the MLNs and colon than CD11a^-/- T cells, whereas T-cell proliferation (as measured by CFSE dilution) was comparable in both populations. Conclusions: Taken together, our data suggest that LFA-1 is not required for EAg-induced activation of CD4⁺ T cells in vitro or in vivo but is required for trafficking of T cells to the MLNs and homing of colitogenic effector cells to the colon where they initiate chronic gut inflammation.