Improvement of long-lasting response and antibody affinity by the complexation of antigen with complement C3b

Complement protein C3 plays a major role in cell regulation and immune response. This last point is mainly due to C3's capacity to act as a bifunctional link between antigen and immunocompetent cells. In a previous work, we have reported the adjuvant effect produced by linking C3 fragments to antigen. In this paper, we characterize the long-term secondary antibody response induced by C3b-antigen complexes. Mice were immunized using either a protein (hen egg lysozyme) or an ovalbumin-derived peptide as antigen. We compared the secondary response elicited by these antigens covalently linked to C3b or emulsified in complete Freund's adjuvant (CFA). Our results provide evidence that C3b linkage induces better long-term adjuvant effect than CFA, resulting in the production of a higher specific IgG titer with a better affinity.