CD6 is a single-member family in the immune system, primarily composed of immunoglobulin-like domains. It is mainly located on the surface of T cells and some B cells, and is expressed in immune organs such as lymph nodes and the spleen. CD6 participates in T cell activation and proliferation, cell adhesion, and movement by interacting with its ligand ALCAM. It regulates immune responses by affecting the T cell receptor (TCR) signaling pathway and cytokine production. Specific gene expression and mutations in CD6 are associated with the occurrence and development of various autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis.