One of a group of proteins on the surface of lymphocytes that enhance immune recognition. Immune cells that express the CD4 molecule are also known as helper T cells; they work with cells that express major histocompatibility complex (MHC) class II molecules to recognize antigens and stimulate cell-mediated and humoral immune responses. The human immunodeficiency virus (HIV) uses the CD4 receptor to infect T lymphocytes, macrophages, and other immunologic cells.
SEE: AIDS; SEE: cluster of differentiation