This product is a FCM antibody cocktail made up of APC Anti-Human CD3 Antibody [Clone: OKT-3] (Mouse IgG2a, κ), FITC Anti-Human CD4 Antibody [Clone: RPA-T4] (Mouse IgG1, κ) and PE Anti-Human CD8a Antibody [Clone: OKT-8] (Mouse IgG2a, κ).; CD3 is a heterotetrameric protein consisting of a CD3γ, a CDδ and 2 CD3ε. It forms complex with TCR. OKT-3 recognize human CD3ε. Human CD3 is expressed on the surface of T cells and NKT cells.; CD4 is also called Leu-3 or T4. It's a single-chain type I transmembrane glycoprotein, mainly expressed on the surface of T cells, and monocytes/macrophages. In T cells, CD4 forms complex with TCR/CD3 and play important roles in T cell immunity. The target of HIV is CD4+ T cells. Reduction of CD4+ T cells is the main reason of defected immunity after HIV infection.; CD8 is mainly expressed on cytotoxic T cells and also some subpopulations of NK cells. CD8 forms dimer function. In most cells, CD8 is a heterodimer consisting of CD8a and CD8b, but in NK cells nearly all CD8 is homodimer of CD8a. CD8a can form co-receptor with MHC-I restricted TCR to promote T cell antigen recognition and activation.