Studies of mixed lymphocyte reactions, surface B cell antigens, and intracytoplasmic immunoglobulins in "null cell" acute lymphocytic leukemia.

Lymphoblasts from "null cell" acute lymphocytic leukemia (ALL) were analyzed for the pattern of proliferation displayed in a mixed lymphocyte reaction (MLR), the presence of a B cell surface antigen, and for the presence of intracytoplasmic immunoglobulin (ICIg). "Null cell" ALL was defined by cytologic and cytochemical criteria and by the absence of spontaneous rosette formation and surface membrane immunoglobulin in cell suspensions of the malignant lymphocytes. In eleven of fourteen patients the proliferative characteristics of lymphoblasts in the MLR were similar to those observed with normal B enriched lymphocytes. In eleven cases studied, anti-B cell serum reacted with a majority of the lymphoblasts. None of the ten cases examined displayed ICIg in the lymphoblasts. We conclude that the "null" lymphoblast from most cases of ALL is a B cell in an early stage of development.