The CD3 epitope is expressed on the epsilon chain of the CD3/T cell antigen receptor (TcR) complex. CD3 is present on 65-85 % of thymocytes and has a mitogenic effect on peripheral blood T cells. Identification of human T cells expressing the 22-28,000 M.W. surface antigen. Identification of CD19 human B cells associated appoximately 10 % of peripheral blood lymphocytes expressing 95,000 M.W. surface antigen