The Appearance of IgM and IgG Cold Agglutinins in Rabbits Hyperimmunized with Group C Streptococcal Vaccine

Abstract

Abstract Rabbits hyperimmunized with Group C streptococcal vaccine developed both IgM and IgG erythrocyte autoantibodies reactive with human type O and rabbit red blood cells at reduced temperatures. Although antibody preparations exhibited maximum agglutinating activity toward human type O and rabbit erythrocytes when assayed at 4°C, significant agglutinating activity toward human type A and sheep erythrocytes was observed when the preparations were assayed at 37°C. The cold agglutinins isolated by thermal elution from rabbit erythrocytes were also effective hemolysins; less than 1.0 μg of IgM was required to sensitize rabbit erythrocytes for 50% lysis in the presence of guinea pig complement (C) in a biphasic-temperature lysis assay. When saccharide haptens, group-specific carbohydrate, and soluble blood group substances were examined for their ability to effect inhibition of lysis, the following pattern was observed. The most effective overall inhibitor was Group C streptococcal carbohydrate, whereas the most effective hapten inhibitor was N-acetylgalactosamine. Of the soluble blood group substances tested, hog mucin H-substance (first Smith degradation product) was slightly more inhibitory than hog mucin A+H-substance (first Smith degradation product) but substantially more active than human ovarian cyst material. Although the soluble blood group substances were capable of competing for rabbit erythrocyte determinants, none gave a visible precipitate in the presence of cold agglutinin when assayed by Ouchterlony double diffusion. In contrast, significant precipitation occurred when cold agglutinin was examined in the presence of Group C carbohydrate in precipitin assays and by Ouchterlony analyses. Results of these studies provide evidence to suggest that the cold agglutinins produced in rabbits hyperimmunized with Group C streptococcal vaccine are a population of group carbohydrate-specific antibodies that are cross-reactive with I antigen-like determinants present on rabbit and human erythrocytes.