CD11d

CD11d, also known as integrin alpha-D (ITGAD), is a subunit of the beta-2 integrin family. It pairs with the β2 subunit CD18 to form the heterodimer CD11d/CD18, commonly referred to as αDβ2. In humans, ITGAD encodes the CD11d protein.

Expression: CD11d is expressed on several leukocyte lineages, with high levels reported on subsets of monocytes and macrophages, and detectable expression on some dendritic cells and granulocytes. Tissue distribution includes circulating leukocytes and sites of inflammation.

Function: As an integrin, CD11d/CD18 mediates adhesion to endothelial cells and extracellular matrix, enabling leukocyte adhesion, rolling, firm arrest, and transmigration during immune surveillance and inflammatory responses. It participates in phagocytosis and possibly in antigen presentation processes. Activation of CD11d/CD18 involves inside-out signaling leading to conformational changes that increase ligand-binding affinity and avidity.

Ligands and regulation: The precise ligand repertoire of αDβ2 includes various intercellular adhesion molecules and matrix components, and can vary by cell type and activation state. Interaction with ligands supports leukocyte trafficking and tissue infiltration during inflammation.

Clinical relevance: Altered expression or function of CD11d/CD18 has been investigated in models of infection, tissue injury, and inflammatory diseases, highlighting its role in leukocyte recruitment and immune regulation. It remains a subject of ongoing research for understanding its contributions relative to other β2 integrins.