Modulating the immune response

Coupling of C3d molecules or ligands of CD21 or CD19 to an antigen alters the level of immune response to the immunogen upon its administration to an individual. For C3d, the magnitude of the effect is dependent on the number of C3d molecules included in the conjugate. Conveniently, C3d molecules or CD21/CD19 ligands are coupled to an immunogen in fusion polypeptides which may be produced by expression from coding nucleic acid, for instance by culturing host cells containing the nucleic acid. Other means of associating the molecules include chemical cross-linking and co-expression on the surface of a carrier structure. Administration of compositions comprising, in a preferred embodiment, C3d molecules and an immunogen of interest may be used prophylactically (by virtue of the immunological memory induced) or therapeutically. The administration may be for the purpose of raising antibodies to the immunogen. A T-cell response may also be induced.