Rat mesangial cells produce granulocyte-macrophage colony-stimulating factor

Because inflammatory processes in renal glomeruli may involve monocyte-macrophages (MPs) and T-lymphocytes, we have investigated whether products of glomerular mesangial cells (MCs) can stimulate the proliferative activity of these effector cells. We found that cultured rat MCs (subcultures 2-15), maintained under serum-free conditions, secrete a soluble factor into the supernate [MC-conditioned medium (CM)], which supports growth of the T-helper cell-derived line HT-2. Moreover, MC-CM increased [3H]thymidine incorporation by thioglycollate-elicited peritoneal MPs but did not induce growth of the interleukin 2 (IL-2)- or interleukin 4 (IL-4)-dependent cell line CTLL-2. Further functional, serological, and biochemical analysis of MC-CM revealed that rat MCs secrete a cytokine that, by all of the techniques used, is indistinguishable from granulocyte-macrophage colony-stimulating factor (GM-CSF). Both northern blot and in situ hybridization with a specific cDNA probe for murine GM-CSF showed that MCs express GM-CSF mRNA transcripts. The present findings indicate that cultured rat MCs produce GM-CSF. Release of GM-CSF by MCs in vivo may play a role in the interaction of MCs with MPs, T-cells, and neutrophils in glomerular disease.