The effect of a4β7 blockade on T-lymphocyte trafficking to intestinal compartments in the normal and inflamed intestine

Abstract

Blockade of the integrin α4β7 has demonstrated promise as an organ specific therapy for the treatment of inflammatory bowel disease (IBD). It is believed that the therapeutic effect of α4β7 blockade is mediated by inhibiting T-cell trafficking into the intestine, however the specific T-lymphocyte compartment affected by α4β7 blockade and the effects of α4β7 blockade on normal T-lymphocyte trafficking and during acute injury are not well understood. In this study we investigated the effect of blocking α4β7 function on the presence of intestinal T-lymphocytes in the diffuse lamina propria and the lymphoid aggregates in the uninflamed intestine, in the acute injury model DSS colitis and the chronic splenocyte transfer model. The presence of intestinal T-lymphocytes in the diffuse lamina propria and lymphoid aggregates was evaluated in wildtype mice, β7-/- mice, and wildtype mice given blocking antibodies to α4β7 or control antibodies using flow cytometry and immunohistochemistry. To evaluate the effect of α4β7 blockade in acute injury, the onset and regression of inflammation, lymphoid aggregate formation and regression and the presence of T-lymphocytes were evaluated in the acute injury model of DSS colitis during α4β7 blockade. To evaluate the effect of α4β7 blockade on T-cell mediated colitis, the course of colitis and the presence of T-lymphocytes in the diffuse lamina propria and lymphoid aggregates was evaluated in the splenocyte transfer model of colitis. In the unchallenged animals, the intestinal T-lymphocyte population in the diffuse lamina propria was normal in the absence of α4β7 function. The T-lymphocyte population in the lymphoid aggregates was also normal with the exception that the Foxp-3 T-lymphocyte population was significantly decreased in the absence of β7. DSS-induced colitis peaked at day 3 after the removal of as DSS demonstrated by increased histological score, MPO activity, and began to regress at day 7 after removal of DSS. The number of B-cell containing lymphoid aggregates peaked at 7 days after the removal of DSS and remained elevated at 14 days after the removal of DSS even though clinical inflammation had regressed. Anti-α4β7 blockade or loss of β7 function dramatically decreased the number B-cell containing lymphoid aggregates, but did not show any other effects, including changes in T-lymphocyte trafficking into the aggregates, during DSS-induced colitis. In the T-cell mediated splenocyte transfer model of colitis, the population of T-lymphocytes in the diffuse lamina propria and the lymphoid aggregates were significantly decreased in β7-/- mice and the wildtype mice receiving α4β7 blockade. This reduction corresponded to the decreased inflammation as evidenced by significant lower expression of TNF-α, IFN-γ, IL-6, MPO and IL-17. The presence of Foxp3+ T-lymphocytes in lymphoid aggregates is dependent upon α4β7, however the trafficking of other T-lymphocytes into the diffuse lamina propria and lymphoid aggregates in the basal state and during acute injury is not dependent upon α4β7. α4β7 blockade can block pathogenic T-lymphocyte trafficking to the intestine in a T-cell mediated model of colitis and accordingly is effective at ameliorating inflammation in this model. These observations suggest that α4β7 blockade may have fewer effects than anticipated on normal T-lymphocyte trafficking and T-lymphocyte trafficking during acute injury and may be a more specific therapy for T-cell mediated inflammatory diseases of the intestine.