In particular, the present invention provides polypeptides comprising the amino acid sequence of residues n-406 of SEQ ID NO:2, where n is an integer in the range of ???20 to 9 and 9 is the position of the first residue from the N-terminus of the complete FcR-I polypeptide (shown in SEQ ID NO:2) believed to be required for receptor binding activity of the FcR-I protein.