SECRETION OF CYTOKINES (INTERLEUKIN-1-ALPHA, INTERLEUKIN-3, AND INTERLEUKIN-6 AND GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR) BY NORMAL HUMAN BONE-MARROW MEGAKARYOCYTES

The effects of cytokine stimulation [recombinant human interleukin (rh IL)-1 alpha, rhIL-3, rhIL-8, rhIL-11, and rh granulocyte-macrophage co lony-stimulating factor (GM-CSF)] on the secretory activity of normal human megakaryocytes were studied by means of the reverse hemolytic pl aque assay (RHPA) in enriched cell preparations. This test facilitates an extremely sensitive determination of cytokine secretion at the sin gle-cell level, together with the clear-cut identification of each imm unostained (CD61) secretory active megakaryocyte. Moreover, the revers e transcriptase-polymerase chain reaction (RT-PCR) was used to investi gate the expression of IL-6, IL-6 receptor (IL-6R), IL-9, IL-10, IL-12 , and IL-13 mRNA in highly concentrated megakaryocyte preparations. In comparison with the spontaneous secretion rate, stimulation with rhIL -1 alpha, rhIL-6, and rhGM-CSF failed to induce a significant increase in the release of cytokines by CD61(+) cells. On the other hand, both rhIL-8 and, in a less pronounced way, rhIL-11 exerted a marked effect on IL-6 secretion. Additionally, after stimulation with rhIL-3, a sig nificant enhancement of the secretion of IL-3 and GM-CSF, but not of I L-1 alpha, could be observed. Using the RT-PCR, a significant inductio n of IL-6 expression could be appreciated in the enriched megakaryocyt e population (60% to 80%) stimulated with rhIL3. The results of this s tudy provide persuasive evidence that a number of cytokines are synthe sized and secreted by human megakaryocytes and not only by hematopoiet ic stroma cells. These data suggest the existence of autocrine and par acrine mechanisms that may influence maturation and differentiation of megakaryocytes as well as act on various stroma cells to sustain an a ppropriate hematopoietic microenvironment. (C) 1995 by The American So ciety of Hematology.