CD103

CD103, also known as integrin alpha E chain, is a protein that forms part of the integrin αEβ7 when paired with the beta7 subunit encoded by ITGB7. It is encoded by the ITGAE gene in humans and is widely used as a marker of mucosal and epithelial-associated lymphocytes and dendritic cells.

Expression of CD103 is prominent on intraepithelial lymphocytes in the gut and other epithelia, including subsets of CD8+ T cells, some CD4+ T cells, γδ T cells, natural killer cells, and certain dendritic cells. In mucosal tissues, Transforming Growth Factor-β (TGF-β) signaling promotes ITGAE expression, contributing to the establishment of tissue residency.

CD103 pairs with β7 to form the αEβ7 integrin, which binds E-cadherin on epithelial cells. This interaction mediates adhesion and retention of lymphocytes within epithelial layers, supporting mucosal immune surveillance, localized cytotoxic responses, and the maintenance of tissue-resident memory T cells (often co-expressing CD69).

In health and disease, CD103+ intraepithelial lymphocytes and CD103+ dendritic cells participate in normal mucosal immunity. Their expansion or activity is observed in inflammatory conditions such as inflammatory bowel disease and celiac disease, reflecting ongoing epithelial immune responses. In cancer, CD103-expressing tumor-infiltrating lymphocytes are associated with a tissue-resident phenotype and have been linked, in several cancer types, to better prognosis and to improved responses to immunotherapy.

CD103 is a useful immunohistochemical marker for identifying tissue-resident T cells and mucosal dendritic cells in research and diagnostic settings.