Immunologic properties of protein-lipopolysaccharide complexes—III: Role of carbohydrate in the LPS adjuvant effect

Abstract

Coupling of the protein antigen lysozyme to lipopolysaccharide (LPS) results in a complex which induces enhanced primary antilysozyme response and enhanced induction of immunological memory. The present experiments were performed to assess the role of the carbohydrate elements of LPS in this adjuvant effect. Periodate oxidized LPS, or LPS derived from an ‘O’ antigen deficient mutant, when used in the preparation of lysozyme-LPS complexes failed to yield complexes which induce enhanced primary antilysozyme responses. Carbohydrate deficiency had no effect on induction of immunological memory. This lack of enhancement of primary responsiveness was not due to any decrease in mitogenicity of the carbohydrate deficient LPS. The primary response adjuvanticity could be restored to complexes containing carbohydrate deficient LPS by secondarily coupling LPS derived carbohydrate elements to these complexes. These results imply that the carbohydrate component of LPS, and the ‘O’ antigen elements in particular, play a central role in enhancement of primary antibody responsiveness to a protein antigen coupled to that LPS.