Integrin alpha E beta 7 consist of two major subunits: Integrin alpha E (ITGAE) also known as CD103 (cluster of differentiation 103) and Integrin beta-7 is an integrin protein that in humans is encoded by the ITGB7 gene. Integrin alpha E beta 7 (CD103) is expressed mainly by cells of the T lymphocyte lineage within mucosal tissues. This is a strikingly narrow pattern of expression compared with that of other integrins. Lymphocytes expressing alpha E beta 7 are abundant in the gut and comprise a major part of the total T cell complement of the body. 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, alpha(E)(CD103)beta(7). This integrin is not a homing receptor, but is thought to retain lymphocytes at the epithelial surface.