Description: The OKT4 monoclonal antibody reacts with human CD4, a 59 kDa cell surface glycoprotein expressed by the majority of thymocytes, a subpopulation of mature T cells (T-helper cells) and in low levels on monocytes. CD4 is a receptor for the human immunodeficiency virus (HIV). The OKT4 antibody recognizes a different epitope than the RPA-T4 monoclonal antibody, and these antibodies do not cross-block binding to each other's respective epitopes.