Residual T lymphocytes, and not malignant B cells, proliferate upon mitogenic stimulation.

Malignant B cells, derived from hairy cell leukemia (HCL), non-Hodgkin's lymphoma (NHL) or prolymphocytic leukemia were stimulated with mitogens and interleukin 2 after careful depletion of contaminating T cells resulting in final residual percentages of less than 0.1. No proliferation was found as measured by 3H-thymidine incorporation. Subsequently, to the non-T B cell cultures very small amounts of autologous or allogeneic T cells were added, ending up in final concentrations of 0.1, 0.5, 1, or 2% T cells. It appeared that a marked proliferation occurred which had in various coculture combinations to be ascribed to the T cells alone. Moreover, most HCL and other B cell NHL additionally stimulated the T cells, resulting in a further increase in proliferation. We conclude that 3H-thymidine incorporation by malignant B cells such as HCL and B-NHL stimulated with mitogens and IL-2 will in most cases wrongly be attributed to proliferation by the B cells themselves, and instead has to be ascribed to contaminating T cells.