Characterization of blood mononuclear and cultured cells in hairy cell leukemia

The nature of neoplastic cells in hairy cell leukemia (HCL) is still controversial. Most reports favor derivation from B cells, but some have suggested origin from monocytes/histiocytes, T cells, or even a hybrid Ig-bearing lymphocyte with phagocytic activity. We established a new cell line from peripheral blood of a patient with typical HCL. The morphologic, immunocytochemical, and functional properties of the new cell line were identical with the patient's original HC. Both cell types demonstrated the irregular, fine cytoplasmic projections characteristic of HC, were weakly phagocytic, markedly positive for tartrate-resistant acid phosphatase, and had variable nonspecific esterase reactivity. Low percentages of EAC-rosetting cells were found (8% original specimen and 6% cultured cells) and a minute amount of IgG, IgA, and IgM were synthesized by the new cell line. A small proportion of cells (13% original specimen and 12% cultured cells) bore SIg when stained with F(ab)2-fragment polyvalent antiserum. Our observations indicated that HC were a slowly proliferating cell population with immunochemical and functional characteristics of both B and monocyte/histiocytic cells.