T lymphocyte function in hairy cell leukaemia.

The high incidence of infections characteristic of impaired cell-mediated immunity in patients with hairy cell leukemia led us to study T lymphocyte function in sixteen patients with the lymphocyte transformation test. All patients showed imparied responses to mitogens, attributable to one or more of the following causes: dilution of responsive T cells by inert hairy cells, shortage of monocytes to give adequate interaction with the T cells and a significant decrease in the number of T cells with Fcmu receptors proportional to the percentage of hairy cells in the peripheral blood. The response to antigens was severely depressed; PPD was one of the few antigens that induced positive reactions in half the cases. We conclude that in patients with hairy cell leukaemia, T lymphocyte function, as tested in a proliferative assay, is severely impaired and that this may contribute to the deficient resistance to infection.