The proteins expressing interleukin 1 (IL 1) activity from rat peritoneal macrophages and cultured glomerular mesangial cells were compared after purification to apparent homogeneity. The purified IL 1 shared a number of biochemical features including m.w., charge, and specific activity. These findings were extended by the results of proteolytic peptide mapping, which revealed similar breakdown oligopeptides, confirming the close resemblance of these two IL 1 species produced by macrophages and mesangial cells. The purified mesangial cell IL 1 acts as an autocrine or paracrine growth factor. The local release of this cytokine may be an important factor in glomerular diseases characterized by mesangial proliferation and matrix expansion.

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