The RPA-T8 monoclonal antibody specifically binds to CD8 alpha (CD8alpha). CD8alpha is a type I transmembrane glycoprotein and a member of the immunoglobulin superfamily. CD8alpha is expressed by the majority of thymocytes, by subpopulations of alphabeta T cells and gammadelta T cells and by some NK cells. Cell surface CD8alpha is expressed either as a disulfide-linked homodimer (CD8alphaalpha) or as a heterodimer (CD8alphabeta) when disulfide-bonded to a CD8 beta chain (CD8beta). CD8-positive alphabeta T cells coexpress both CD8alphaalpha homodimers and CD8alphabeta heterodimers whereas some gammadelta T cells and NK cells express CD8alphaalpha homodimers. CD8 plays important roles in T cell activation and selection. The extracellular IgSF domain of CD8alpha binds to a non-polymorphic determinant on HLA class I molecules (alpha3 domain) and enables CD8 to function as a co-receptor with MHC class I-restricted TCR during T cell recognition of antigen. The cytoplasmic domain of CD8alpha associates with Lck, a Src family protein tyrosine kinase that is involved in intracellular signaling. The RPA-T8 and HIT8a (Cat. No. 555337) monoclonal antibodies are not cross-blocking. Synonyms: CD8alpha, CD8A, CD8 alpha, Leu2, MAL, T8, p32