Platelet-derived growth factor (PDGF) activates primitive hematopoietic precursors (pre-CFCmulti) by up-regulating IL-1 in PDGF receptor-expressing macrophages.

Platelet-derived growth factor (PDGF-BB) is known to stimulate growth of fibroblasts and smooth muscle cells via interaction with specific PDGF-B receptors on their surfaces. Hematopoietic precursor cells are not known to respond directly to PDGF, and PDGF receptors have never been reported on normal hematopoietic cells. We report a consistent stimulatory effect of PDGF-B on primitive pluripotential hematopoietic cells (pre-CFCmulti) in suspension cultures of mouse bone marrow that resembles effects obtainable previously only with IL-1. Further, we show that the effect depends on plastic-adherent accessory cells and is abrogated by neutralizing antibodies to IL-1 beta, that PDGF strongly up-regulates IL-1 mRNA levels in marrow macrophages but not in marrow fibroblast lines, and finally provide a first report of expression of RNA transcripts for PDGF-B receptors in normal marrow macrophages. Together, the results suggest the existence of a novel cytokine loop implicating monocyte/macrophages as cells reactive to PDGF and highlighting IL-1 induction as a significant feature of their PDGF response.