Leustroducsin B, a New Cytokine Inducer Derived from an Actinomycetes, Induces Thrombocytosis in Mice

Leustroducsin B (LSN-B), a novel colony-stimulating factor (CSF) inducer produced by an actinomycetes, has previously been shown to induce CSF production in bone marrow stromal cells. To determine the biological activity of LSN-B on hematopoiesis in vivo, LSN-B was administered intraperitoneally to mice every day for three to six days. Peripheral platelet counts were markedly elevated on days 4 through to 6 compared with the control mice injected with vehicle. Serum IL-6 levels were low (0.8 ng/ml) or virtually undetectable in the drug treated groups. This cytokine profile suggests that LSN-B induction of thrombocytosis is mechanistically distinct from other cytokine inducers such as IL-1 or FK-565.