CD4 membrane glycoprotein of T lymphocytes.The CD4 antigen acts as a coreceptor with the T-cell receptor on the T lymphocyte to recognize antigens displayed by an antigen presenting cell in the context of class II MHC molecules. CD4 is an accessory protein for MHC class-II antigen/T-cell receptor interaction. It plays an important role in T helper cell development and activation. CD4 serves as a receptor for the human immunodeficiency virus HIV.
