Agglutinating and non-agglutinating antibodies in rabbits inoculated with a particulate antigen (Salmonella typhimurium).

Agglutinating and non-agglutinating anti- antibodies were specifically purified from the sera of immunized rabbits. Both types of antibody had the same electrophoretic mobility and were localized in the IgG fraction. It was not possible to find antigenic differences between agglutinating and non-agglutinating antibodies by immunodiffusion. Agglutinating antibody activated the complement system, while non-agglutinating antibody lacked this capacity. Only the former increased clearance of antigen from the blood. When serum samples with different antibody titres determined by agglutination (agglutinating antibody) and Coombs test (non-agglutinating antibody) were injected in mice, clearance of antigen from the blood showed changes. These results were similar to those previously observed by us when different precipitating: co-precipitating antibody ratios were used, and indicated that competition of both antibodies for the antigen depends on their respective amounts. When mice protection tests were set up by injection of agglutinating and non-agglutinating antibody before the inoculation of 10 LD , non-agglutinating antibody was found to be less effective than agglutinating antibody. Non-agglutinating antibody was detectable during the whole course of immunization. Its serum concentration was higher than that of the agglutinating antibody. Non-agglutinating antibody behaves in a similar way to co-precipitating antibody. The initially proposed hypothesis that such antibodies could interfere with immunity to certain chronic infections was extended to include the non-agglutinating antibodies demonstrated here.