Human Membrane-bound C3 Receptors I. Serological and Immunohistological Demonstration of C3 Receptors

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Abstract
The study presents evidence of the specific reactivity of an anti-C3 [complement component 3] receptor serum (AC3RS), demonstrates membrane-bound C3 receptors by using this AC3RS in different serological and immunohistological methods and investigates the relationship between membrane-bound C3 receptors and .alpha.1-antitrypsin. The AC3RS, or IgG fraction F(ab'')2 fragments of this antiserum, stained a percentage of various viable cell populations roughly equivalent to the cells number that bound EAC3b [erythrocyte-antibody-C3b complex] and/or EAC3d; C3 receptor-negative T cells and thymocytes were not stained. On frozen sections of tonsils and kidneys the AC3RS stained the area to which EAC3b adhered. After absorption with neutrophils or Ehu, the AC3RS inhibited the EAC3d agglutination 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. .alpha.1-Antitrypsin antisera failed to inhibit EAC agglutination with C3 receptor-bearing cells or to stain C3 receptor-positive cells either in suspension or in frozen sections. AC3RS absorption with purified .alpha.1-antitrypsin did not affect its specific reactivity.