Symposium on membrane markers and antigens of human lymphocytes and leukemic cells.

B lymphocytes, mediators of humoral immunity, carry easily detectable SIg, form rosettes with RBC coated with IgM and complement (EAC rosetting) and bind aggregated Ig (Fc receptor activity). Human T lymphocytes, mediators of cellular immunity, lack a specific antigen found on mice T lymphocytes (theta antigens). They form spontaneous (non-immune) rosettes with SRCB (E rosetting) and they are identified by labelling or cytotoxicity tests wtih heterologous antisera. Apart from B and T lymphocytes, a third population of lymphoid cells carrying no detectable surface markers have been identified by various methods (Null cells).