Studies of Lymphocyte Proliferation in Hairy Cell Leukaemia: Activity in Mixed Lymphocyte Reaction and Responses to Mitogens

S ummary . Subpopulations of splenic lymphocytes from patients with hairy cell leukaemia (HCL) were compared with similar subpopulations of lymphocytes from reference individuals for their ability to respond to mitogens and to participate in allogeneic and autologous mixed lymphocyte reactions. T cell enriched subpopulations were obtained by double passage of mononuclear cells through nylon wool columns. Non‐T cell subpopulations were collected by eluting adherent cells from nylon wool columns and by incubating them with sheep erythrocytes followed by density gradient centrifugation. Unfractionated mononuclear cells, T enriched and non‐T subpopulations were compared. Enriched T cell subpopulations from HCL and reference patients responded similarly to allogeneic antigens and phytohae‐magglutinin. Splenic non‐T cells from reference patients produced a stronger stimulus in the allogeneic mixed lymphocyte reaction than did the unfractionated or the T enriched cells. In contrast, the non‐T subpopulations from patients with HCL produced a reduced response compared to that of reference splenic cells when mixed with allogeneic lymphocytes. In addition, non‐T cells from HCL patients failed to respond to pokeweed mitogen. Neither reference nor HCL splenic cells produced a significant response in the autologous mixed lymphocyte reactions. The data suggest that splenic non‐T cells from patients with HCL either suppress the stimulatory capacity of normal B lymphocytes or fail to stimulate allogeneic lymphocytes in the mixed lymphocyte reactions.