There is provided an isolated, soluble polypeptide comprising an amino acid sequence having at least 90% sequence identity with a polypeptide region selected from the group consisting of: amino acid residues 36-301 of SEQ ID NO:40; amino acid residues 43-310 of SEQ ID NO:42; amino acid residues 21-286 of SEQ ID NO:44; or amino acid residues 21-286 of SEQ ID NO:46; wherein said polypeptide is capable of specifically binding the Fc region of IgG.