An active polypeptide includes the amino acid sequence of SEQ ID NO:3, or having at least 50%, preferably 70%, more preferably 90% identity with the amino acid sequence of SEQ ID NO:3, or fragments thereof having at least 20 contiguous amino acids, or peptides having at least 50%, preferably 70%, more preferably 90% identity with the amino acid sequence of the fragments, provided that the polypeptide is not SEQ ID NO:2.