The invention relates to a product which comprises a C4bp domain of a non-mammalianorigin, particularly SEQ ID NO:1, SEQ ID NO:23 or SEQ ID NO:37, or a variant thereof,and an antigen. The product is desirably in the form of a fusion protein. The chickenC4bp domain of SEQ ID NO:1 and SEQ ID NO:23 is also described. Antigens includemonomeric antigens such as malarial and influenza antigens. The C4bp domainprovides for assembly of multimeric complexes of the antigen, or mixtures thereof.The complexes are useful as vaccines.