Hyperimmune Response to a Protein and a Polypeptide Antigen Coated on Pneumococcus R36A

Bacterial stimulation of the immune response is a well known but incompletely understood phenomenon (1). The most successful method used to enhance the immunogenicity of protein and polypeptide antigens has been the use of complete Freund's adjuvant. However, the levels of antibody generally produced in rabbits are far below those reported for carbohydrate antigens when they are part of a formalinized suspension of whole bacteria (vaccine). Intensive intravenous (i.v.) immunization of rabbits with either streptococcal or pneumococcal vaccines often results in levels of 5 to 20 mg of antibody/ml serum which is directed mainly against the surface polysaccharides (2–4). An explanation for this vaccine effect is that the bacterial cell serves as the “carrier” for bacterial polysaccharide which can be considered a hapten attached to the bacterial surface. We have examined the possibility that a bacterial cell might serve as a nonspecific carrier for antigens adsorbed onto the cell surface.