Hairy Cell Leukemia: A Case with B-lymphocyte Origin

To categorize the neoplastic cells in hairy cell leukemia, extensive studies were performed on peripheral blood and splenic lymphocytes from a patient with this disorder. Using purified suspensions, containing 90–100% hairy cells, these cells lacked monocytic features. Although they did adhere to glass, they did not phagocytize IgG or C3-coated erythrocytes and showed only limited capacity to ingest latex particles. Granulocyte colony-stimulating factor, which is elaborated by both normal and neoplastic monocytes, was not produced by the patient’s hairy cells. Many cell surface immunoglobulins were detected on cells examined immediately after separation, but following incubation in serum-free medium, there was a decrease in all markers except γ chains. After a 24-hour incubation, γ chains were identified on the surface of 95% of the cells. In addition, 90% of cells examined either immediately or after incubation showed only γ heavy chains intracellular!}. Assays of complement receptors suggested the predominance of mouse complement receptors on the neoplastic mononuclear cells. The hairy cells did not form rosettes with sheep erythrocytes and did not respond to phytohemagglutinin. By electron microscopic criteria, the leukemia cells had the structural appearance of lymphocytes. These results are consistent with the concept that, in this patient, hairy cell leukemia represents a variant of a B-cell neoplasm.