Human serum immunoglobulin G3 subclass bound preferentially to asialo-, agalactoimmunoglobulin A1/Sepharose

As we reported before, exoglycosidase treatment of human serum IgA1 changed it to a sticky molecule. In order to examine the presence of the specific binding protein to the sticky IgA1 in human serum, IgA1, asialo-IgA1 (IgA1- S) and asialo-, agalacto-IgA1 (IgA1-SG)/Sepharose column chromatography of normal human serum was carried out. Purified hinge glycopeptide (HGP33) pre pared from IgA1 was used for the preparation of HGP/Sepharose. A portion of the serum protein was bound to those columns and eluted with the buffer co ntaining 1.0 M NaCl. About four times the amount of protein was eluted from the IgA1-SG/Sepharose column than that from IgA1/Sepharose. Most of the el uted protein was IgG, and the IgG1 and IgG3 subclasses but neither IgG2 nor IgG4 was dominant. Under the lower salt concentration, a portion of IgG wa s also bound to the HGP-SG/Sepharose column. The obtained results coincide well with the previous report of the co-present of IgG1 and IgG3 with depos ited IgA1 in IgA nephropathy patients (Aucouturier, P., ef al. (1989) Clin. Immunol. Immunopathol. 51., 338-347), Thus, the results solved the questio n of why the IgG3 was co-present with deposited IgA1 in IgA nephropathy pat ients. (C) 1999 Academic Press.