Interleukin 6 is an autocrine growth factor for mesangial cells

Interleukin 6 (IL-6) induces the acute phase response, differentiation of B cells, proliferation of T cells, thymocytes, hematopoietic progenitors, hybridoma and plasmacytoma cells. Monocytes, T cells, fibroblasts, epithelial and endothelial cells secrete IL-6. Since IL-6 responsive cell-types may participate in the pathogenesis of glomerular inflammation, we studied the secretion of IL-6 by rat MCs, using the IL-6 dependent hybridoma cell line B9. The results of our studies indicate that MCs secrete IL-6 with a molecular weight of 17-42 kDa and isoelectric point of 4.0 to 5.3 MC-IL-6 activity could be blocked by a polyclonal antimurine-IL-6 antibody. MC express IL-6 mRNA as determined by Northern blot. Furthermore, our data demonstrate that IL-6 acts as an autocrine growth factor for MC. Incubation of subconfluent MC with recombinant IL-6 results in a dose-dependent increase of 3H-thymidine incorporation and number of MCs. Moreover, reverse phase HPLC fractions of MC-CM containing IL-6 activity increase 3H-thymidine incorporation by MC. In addition to its possible paracrine role in mediating the immune response in the glomerulus, MC-IL-6 may also be one of the autocrine signals leading to mesangial cell proliferation in vivo.