Goat polyclonal antibody to CD4. CD4 is a member of the immunoglobulin superfamily, a membrane glycoprotein of T lymphocytes that interacts with major histocompatibility complex class II antigens and a receptor for the human immunodeficiency virus. This protein is expressed not only on the surface of T helper cells and regulatory T cells but also on monocytes, macrophages and dendritic cells. It functions to initiate or amplify the early phase of T-cell activation and may function as an important mediator of indirect neuronal damage in infectious and immune-mediated diseases of the central nervous system.