Rat Anti- Mouse CD5/Ly- 1- FITC(0.5 mg)

CD5/Lyt-1 antigen 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.^1-3 It has been identified as the major ligand of the B-cell antigen CD72.^{4, 5} 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 (reviewed in 6). 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.^7-12 It has been proposed that CD5 negatively regulates signal transduction mediated by the T-cell and B-cell receptors.^{13, 14}