Expression of a protective intestinal immune response can be inhibited at three distinct sites by treatment with anti-α4 integrin

The α4 integrins mediate lymphocyte adhesion to Peyer's patch high endothelial vessels and homing to Peyer's patch, as well as to mesenteric lymph nodes. In rats, immunity to infection with the nematode Trichinella spiralis is known to be mediated by CD4⁺ OX22^- (CD45RC^-) cells that home to the intestine in large numbers. These experiments were conducted to determine whether the α4 integrins or LFA-1 were involved in the expression of intestinal immunity to T. spiralis. Injection of the anti-α4 integrin, mAb TA-2, but not anti-LFA-1, mAb TA-3, impaired the expression of immunity. An effect of TA-2 was measured at three distinct sites along the activation pathway leading to the migration of protective CD4⁺ OX22^- cells to the intestine. Injection of TA-2 on the same day as infection prevented normal rejection of the parasite and abrogated the characteristic appearance of blast cells in draining lymph 3 days after infection. A similar effect on the migration of blast cells at day 3 was seen when TA-2 was injected 1 day after infection, and injection 2 days after infection still reduced the number of protective cells entering TD lymph on day 3. The effect of TA-2 and TA-3 on homing of dividing cells to the gut was examined by injecting dividing cells i.v. at the same time as antibody. Under these conditions migration of dividing cells to the gut was reduced by 90 to 95% and their capacity to adoptively transfer worm rejection blocked. Furthermore, TA-2 treatment also inhibited protection when it was injected 12, 18, or 24 h after the transfer of protective cells, when these cells had already entered the gut, but not when TA-2 injection was delayed for 36 h. These results indicate the involvement of α4 integrins at the following points in the generation, dissemination, and function of CD4⁺ OX22^- effectors: 1) initial activation during the first 48 h of infection; 2) migration of protective cells to and extravasation in the gut; 3) a function after entry into gut tissues. The results suggest that entry of dividing cells into the gut is critical for the adoptive transfer of protection and that α4 integrin has multiple roles in the manifestation of intestinal immunity.