LEUSTRODUCSIN-B, A NEW CYTOKINE INDUCER DERIVED FROM AN ACTINOMYCETES, INDUCES THROMBOCYTOSIS IN MICE

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