The invention relates to fusion proteins comprising an amino acid sequence of a fragment H corresponding to a fragment of a calcium binding protein excreted-secreted by adult worms of Fasciola hepatica, followed by an amino acid sequence corresponding to a unrelated protein or fragment of protein, pharmaceutical compositions, vaccines and adjuvants containing the immunogen, to a process for their preparation, another process for the production of antibodies and their use.The present invention relates to the preparation of immunogens by the addition of a peptide sequence.Thus the present invention is useful for producing an immune response, with increases in specific antibody titers in serum against proteins or other antigens and can be applied in particular for the production of specific polyclonal antibodies, immunotherapy and immunoprophylaxis. The addition of the polypeptide to a target antigen, either through the production of recombinant proteins containing the polypeptide or by addition or fusion of this polypeptide with the target antigen, induces a significant increase in the immunogenicity of these molecules, amplifying the immune response elicited by injection of this molecule in a subject susceptible to produce antibodies.