Glomerular macrophage proliferation in experimental immune complex nephritis

In immune complex nephritis, glomerular hypercellularity is known to result from the proliferation of intrinsic cells and from the infiltration of mononuclear cells, primarily macrophages. An immunohistochemical double-labeling procedure was used to determine whether macrophages were among the cells which may undergo mitosis within the glomerular tuft. The monoclonal antibody ED1 served as a macrophage marker; cells in the S-phase of mitosis were recognized by uptake of bromodeoxyuridine. Glomerular proliferation was studied in chronic serum sickness of LEW rats, an animal model of immune complex nephritis for which the relationship between immunopathology and pathophysiology has been well described. In normal glomeruli, resident mesangial macrophages accounted for an unexpectedly large proportion (≥one-third) of the total mitotic activity. In immune complex glomerulonephritis, the rate of glomerular macrophage proliferation increased rapidly just at the onset of proteinuria and remained high throughout the remaining course of disease. Glomerular macrophages from rats with proliferative nephritis also divided more vigorously than normal in short term culture in vitro, while persistently expressing abnormal surface marker phenotypes. The proliferation of mesangial macrophages appears to be a prominent feature of the normal process of glomerular cell renewal. In hypercellular glomeruli, vigorous local proliferation could greatly amplify the potential of macrophages to cause damage.