Serum inhibitor for bacterial red cell sensitizing antigens.

Substances that can combine with and prevent red cell sensitization by various streptococcal and Gram-negative bacillary antigens are demonstrable in normal human serum. The inhibitors combining with two serologically distinct streptococcal sensitizing antigens—Hickey and 8029—were found to be heat stable, not precipitable by trichloracetic acid, non-antigenic in the rabbit, separable on Sephadex G-200 and by starch block electrophoresis from both serum albumin and serum γ-globulin and, unlike influenza virus haemagglutination inhibitor, not inactivated by trypsin, periodate or a bacterial () receptor-destroying enzyme. The inhibitors were specifically absorbable by the homologous bacterial cells but the antigen groups determining this specificity were distinguishable from those that combined with homologous antibody. Inhibitors combining with the red cell sensitizing antigens of the Gram-negative bacteria examined appeared to have similar properties but were not found to be absorbable by homologous bacterial cells.