CD4 is a 55-kD glycoprotein expressed on the surface of T helper/regulatory T cells, monocytes, macrophages and some dendritic cells. The majority of peripheral T-cell lymphomas originate from the T helper/regulatory cell subset, so most mature T-cell neoplasms are CD4+. Anti-CD4 is used to identify normal T cells and to help identify neoplasms of T cell origin.