Recirculation and Homing of Lymphocyte Subsets: Dual Homing Specificity

The p7-integrin subunit can pair with two a-chains, a4 and aE, and is expressed mainly on lymphocytes. As an a4-heterodimer it binds to the mucosal addressin MAdCAM-1, thus acting as a mucosal homing receptor. As an aE-heterodimer it binds to E-cadherin and is mainly found on intestinal intraepithelial lymphocytes. Consequently, p7 is mostly expressed on lymphocytes of the mucosal immune system. To study the compartmentalization of these cells further we compared the distribution of such lymphocytes in two strains of mice (BALBIc and NOD) and found that the distribution of p7-positive lymphocytes among various lymphoid tissues in these strains was very different. In NOD mice a conspicuous population of p7-integrinhigh lymphocytes expressing either a4, aE, or both, was found in nonmucosal lymphoid tissues such as peripheral lymph nodes (PLNs). They mostly expressed the PLN homing receptor L-selectin, and included both naive and memory cells on the basis of