Expression of 'pan T cell' cell surface antigens by T lymphocytes occurs in the following sequence: CD7 (early prothymocyte); CD2 (midprothymocyte); CD5 (immature thymocyte), cytoplasmic CD3 (immature and common thymocyte) and CD3 (mature thymocyte).2,6 This is followed by coexpression (common thymocyte) and then distinct expression (mature thymocyte) of CD4 (inducer) and CD8 (suppressor/cytotoxic) cell surface antigens.2,6 Once expressed, the CD7, CD2, CD5 and CD3 antigens with either CD4 or CD8 are coexpressed continuously throughout the remainder of T lymphocyte differentiation including both the resting and the activated mature peripheral blood or lymphoid tissue T lymphocyte.