CD5 Antibody [B19.1]

CD5, also known as Lyt-1, is a monomeric type I transmembrane glycoprotein expressed on thymocytes, T lymphocytes, and a subset of B lymphocytes, but not on natural killer (NK) cells. It has been identified as the major ligand of the B-cell antigen CD72. The frequency of CD5+ B cells exhibits strain-dependent variation, and the phenotypic, anatomical, functional, developmental, and pathological characteristics of the CD5+ B cells suggest that they may represent a distinct lineage, known as B-1 cells. Binding of CD5 on the T cell surface can augment alloantigen- or mitogen-induced lymphocyte proliferation and induces increased cytosolic free calcium, IL-2 secretion, and IL-2R expression. It has been proposed that CD5 negatively regulates signal transduction mediated by the T-cell and B-cell receptors.