CD11a

CD11a, also known as integrin alpha L chain or ITGAL, is a cell surface protein that forms the LFA-1 integrin when paired with the beta-2 subunit CD18 (ITGB2). LFA-1 mediates leukocyte adhesion to the vascular endothelium and to antigen-presenting cells, and it supports the formation of immunological synapses between T cells and antigen-presenting cells. This function is central to leukocyte trafficking, migration into tissues, and effective immune responses.

CD11a is a type I transmembrane glycoprotein expressed primarily on leukocytes, including T cells, B cells, natural killer cells, neutrophils, monocytes, and dendritic cells. It is not typically found on erythrocytes. As part of LFA-1, CD11a binds intercellular adhesion molecules ICAM-1, ICAM-2, and ICAM-3, promoting firm adhesion and transmigration during inflammation. LFA-1 activity is regulated by inside-out signaling and can shift between low- and high-affinity conformations; binding interactions are stabilized by divalent cations such as calcium and magnesium.

Clinical and research relevance: Disruption of LFA-1 function involving ITGAL can impair leukocyte adhesion and trafficking, contributing to altered immune responses. CD11a serves as a surface marker in immunophenotyping to identify leukocyte subsets. Therapeutic modulation of LFA-1 has been investigated for inflammatory diseases and transplantation, though certain approaches have encountered safety concerns.