Defective autologous and allogeneic mixed lymphocyte reactions in hairy cell leukaemia.

The autologous and allogeneic mixed lymphocyte reactions were measured using peripheral blood cells from 13 patients with hairy cell leukaemia (HCL), six of whom had been splenectomized when first studied. T cells from five patients responded to autologous stimulation, and one of these had received splenectomy. Significant alloreactivity was observed in nine patients, of whom three were splenectomized. An absent autologous reaction was associated with ratios of OKT4:OKT8 positive cells less than 1.5, and such ratios were more often observed after splenectomy. Non-T cells from 10 of 11 patients stimulated allogeneic normal T cells. The amounts of HLA-DR antigens on hairy cells were similar to those on normal peripheral blood non-T cells. These data suggest that the defects of response in HCL reflect abnormalities at the responder T cell level. Such defects may contribute to the defective host defence frequently observed in HCL.