The nature of non-precipitating antibodies.

The continuous formation of antibodies over long periods of time after immunization of animals with certain toxoids and bacterial polysaccharide (1, 2), dextran and blood group substances (3), and viruses (4), is well documented. More recently, antibodies of the nonprecipitating type have been shown to persist in the circulation of rabbits following immunization with serum protein antigens (5). In a previous study, it was shown that the non-precipitating antibodies could not be differentiated from the precipitating antibodies on the basis of their electrophoretic, sedimentation and salting out properties (6), although it was demonstrated that they, unlike the precipitating type, could not sensitize guinea pigs to anaphylactic shock in vitro (7)