Stimulation of human myelopoiesis by leukotrienes B4 and C4: interactions with granulocyte-macrophage colony-stimulating factor

The regulatory role of leukotrienes (LT) on human myelopoiesis was investigated. Mononuclear bone marrow cells from 31 healthy donors were cultivated in the presence of suboptimal concentrations of recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) for 10 days in semisolid agar. The addition of LTC4 or LTB4 to the cultures dose- dependently stimulated myeloid stem cell proliferation. Maximal effects were observed at 10(-8) mol/L, at which LTC4 induced a 91% +/- 23% (mean +/- SEM; P = .004) and LTB4 a 73% +/- 22% (P = .008) increase in colony formation. In contrast, addition of the LTB4 isomer 5(S), 12(S)- diHETE did not affect the growth. LTD4 exerted a weak potentiating effect on progenitor proliferation (17% +/- 7% growth stimulation at 10(-10) mol/L; P = .034), whereas LTE4 was without consistent effect. Furthermore, LTC4-induced stimulation of colony formation was insensitive to the LTD4 antagonist ICI 198615. The dual lipoxygenase and prostaglandin endoperoxide synthase inhibitor CL42A potently suppressed the proliferation of myeloid colonies, a suppression that could be reversed by parallel addition of LTB4 or LTC4. The results suggest that both LTB4 and LTC4 possess strong and specific synergistic stimulatory effects on GM-CSF-induced human myeloid progenitor cell growth.