The 2E7 monoclonal antibody specifically recognizes CD103 which is also known as the α chain of the heterodimeric αIELβ7 (also known as, αEβ7) integrin. CD103 is a type I transmembrane glycoprotein that is encoded by Itgae (integrin alpha E, epithelial-associated). CD103 has a unique and fairly restricted tissue distribution. It is expressed on almost all intestinal intraepithelial lymphocytes (IEL), dendritic epidermal T cells (DEC), subsets of peripheral T cells, and distinct subsets of fetal, neonatal, and adult thymocytes. E-cadherin is the epithelial cell ligand for αIELβ7 integrin. The ordered expression of αIEL during thymocyte development (which occurs under the influence of the thymic epithelium), high level of αIEL expression on peripheral T cells in epithelial tissues (IEL and DEC), and expression of CD103 on a subset of CD8+ lymphocytes responding to allogeneic epithelial cells, suggest that αIELβ7 integrin has a common role in the interactions of T lymphocytes with epithelia during T-cell maturation and effector functions. CD103 is thought to play a role in allograft rejection. The 2E7 antibody recognizes a different epitope than that recognized by the M290 antibody. Ligation of CD103 by 2E7 reportedly induces intracellular signaling activity in a redirected lysis assay and can costimulate anti-TCR antibody-activated IEL and CD8+ T cells. The 2E7 hamster antibody does not crossreact with rat leucocytes.