Role of the mucosal integrin α E (CD103)β 7 in tissue‐restricted cytotoxicity

Summary The effectiveness of lung transplantation is marred by the relatively high incidence of rejection. The lung normally contains a large population of lymphocytes in contact with the airway epithelium, a proportion of which expresses the mucosal integrin, α E (CD103)β 7 . This integrin is not a homing receptor, but is thought to retain lymphocytes at the epithelial surface. Following transplantation, a population of ‘tissue‐restricted’ cytotoxic T cells (CTL) have been identified which have the ability to lyse epithelial cells, but not major histocompatibility complex (MHC)‐identical splenic cells. We tested the hypothesis that expression of the mucosal integrin confers the ability of CTL to target and destroy e‐cadherin expressing targets. Immunohistochemical and flow cytometric analyses were used to demonstrate the relevance of this model to human lung. Allo‐activated CTL were generated in mixed leucocyte reactions and CD103 expression up‐regulated by the addition of transforming growth factor (TGF)‐β. The functional effect of CD103 expression was investigated in 51 Cr‐release assays using e‐cadherin‐expressing transfectant targets. Human lung epithelial cells express e‐cadherin and one‐third of intraepithelial lymphocytes (IEL) expressed CD103. Allo‐activated and bronchoalveolar lavage (BAL) lymphocytes express more CD103 than those in blood. Transfection of e‐cadherin into murine fibroblasts conferred susceptibility to lysis by α E β 7 ‐expressing CTL which could be blocked by specific monoclonal antibodies to CD103 and e‐cadherin. CD103 functions to conjugate CTL effectors to e‐cadherin‐expressing targets and thereby facilitates cellular cytotoxicity. E‐cadherin is expressed prominently by epithelial cells in the lung, enabling CTL to target them for destruction.