CD4 is a 51 kDa membrane glycoprotein that is expressed on subsets of thymocytes and mature T lymphocytes where it works as co-receptor for T-cell receptor and interacts with MHC Class II processed antigens. CD4 is also expressed on surface of monocytes, macrophages and dendritic cells. CD4 also regulates T-cell activation and differention. CD4 is identified as the cellular receptor for HIV and several other viral infections. CD4 is highly expressed in thymus, spleen and lymphocyte.
