Human membrane-bound C3 receptors. I. Serological and immunohistological demonstration of C3 receptors.

The aim of the present study was to present further evidence of the specific reactivity of an anti-C3 receptor serum (AC3RS), to demonstrate membrane-bound C3 receptors by using this AC3RS in different serological an immunohistological methods, and to investigate the relationship between membrane-bound C3 receptors and alpha1-antitrypsin. The AC3RS, or F(ab')2 fragments of the IgG fraction of this antiserum, stained a percentage of various viable cell populations roughly equivalent to the number of cells that bound EAC3b and/or EAC3d; C3 receptor-negative T cells and thymocytes were not stained. On frozen sections of tonsils and kidneys it was found that the AC3RS stained area to which EAC3b adhered. After absorption with neutrophils or Ehu, the AC3RS inhibited the agglutination of EAC3d with tonsil cells, but not the agglutination of tonsil cells or neutrophils with EAC3b; this absorbed AC3RS still stained tonsil cells but not neutrophils, and in frozen tonsil sections it stained only those areas to which EAC3d adhered. The absorbed AC3RS did not stain glomeruli. Antisera to alpha1-antitrypsin failed to inhibit EAC agglutination with C3 receptor-bearing cells or to stain C3 receptor-positive cells either in suspension or in frozen sections. Absorption of th AC3RS with purified alpha1-antitrypsin did not affect its specific reactivity.