Immune complex degradation by cultured rat mesangial cells

The binding and degradation of radiolabelled immune complexes by cultured rat glomerular mesangial cells were measured and compared with the binding and degradation by thioglycollate-elicited rat peritoneal macrophages. Mesangial cells are generally considered to be a modified pericyte with smooth muscle-like properties, but they were able to bind and degrade soluble immune complexes at rates comparable to those of the macrophages. In a second study, the ability of cultured mesangial cells to bind and degrade immune complexes of varying molecular weight was assessed. Very large, insoluble complexes were found to bind to mesangial cells more avidly than small soluble complexes, but unlike the small complexes, the large complexes did not appear to undergo degradation. These findings support a role for the intrinsic mesangial cell in the elimination of small soluble immune complexes as they arrive in the glomerulus. They also provide a possible explanation for the paradox that large immune complexes--i.e., electron-dense deposits--can persist in the mesangium next to the intrinsic mesangial cells without being rapidly destroyed.