A Study of the Receptor for Complement in the Human Renal Glomerulus

Abstract

A study of complement receptor (GCR) was performed in the human renal glomerulus in normal and various pathologic situations. Frozen section of 4μ thickness were incubated with two kinds of the indicator cells, namely sheep erythrocyte coated with IgM antibody and C3 (EAC3b) and fluorescein-labeled bacteria coated with C3 (FBC), in order to determine the activity of GCR. Numerous EAC3bs adhered specifically to the glomeruli under the light microscope. On the other hand, the sections were incubated with FBC and tetramethyl rhodamine isothiocyanate (TRITC)-labeled anti-human GBM antibody. The double-stained specimens under the immunof luorescent microscope (IF) showed that FBCs were bound to the external (or epithelial) side of GBM. Furthermore, frozen sections of 12μ thickness were incubated with EAC3b and FBC, and were observed under the scanning electron microscopes It was noted that the indicator cells adhered to the surface of glomerular epithelial cells. The C3 deposits under IF and the C3 receptor activity for binding of EAC3b were examined inn the glomeruli of sixty-six biopsy specimens from various renal diseases The loss or reduction of GCR activity was detected in twelve cases (acute glomerulonephritis 3, lupus nephritis 4, membranous nephropathy 3, membranoproliferative glomerulonephri.tis 2), of which eleven cases revealed subepithelial C3 deposits. However, the restoration of GCR activity did not occure removal of C3 deposits by acid treatment. The GCR activity was noticed even after incubation with fresh serum and urine of patients with various renal diseases. In conclusion, the GCR is located on the epithelial cells of the glomerulus and its activity is closely related subepithelial C3 deposits. It seems that the GCR may play an important role in trapping and deposition of immune complexes containing complement in immunologically mediated renall diseases.