Altered heterogeneity of monocytes in acute myelomonocytic leukemia

Human peripheral blood monocytes isolated from normal donors and patients with acute myelomonocytic leukemia (AMML) were separated on a discontinuous density gradient of bovine serum albumin (BSA) into five fractions. Cells from each fraction were assayed for cell surface markers, prostaglandin E2 (PGE2) production, ability to affect proliferation in response to antigen by autologous peripheral blood lymphocytes previously depleted of monocytes, and ability to regulate immunoglobulin (Ig) synthesis by allogeneic B-lymphocytes. Fractions 1-5 from normal donors contained 11, 10, 23, 34, and 22%, respectively, of the total number of monocytes. In contrast, in 6 patients with AMML fraction 3 was considerably larger (52%) than any other fraction, in 1 patient comprising 87% of her monocytes. Cells from each fraction differed markedly in accessory function. In general, cells from fraction 3 were poorer as helper cells than cells from other fractions. They also produced after stimulation larger amounts of PGE2 than did cells from other fractions of the gradient. These data show that PBL contain a subpopulation of monocytes, which either helps poorly or suppresses in vitro immunologic function of T-cells (proliferation) and B-cells (lg synthesis), and that this subpopulation is increased in the blood of patients with AMML.