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Biochem Biophys Res Commun. 1999 Oct 22;264(2):424-9.

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

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Department of Biochemistry, Kitasato University, Sagamihara, Kanagawa, 228-8555, Japan.


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) prepared 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 containing 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 eluted 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 was 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 deposited IgA1 in IgA nephropathy patients (Aucouturier, P., et al. (1989) Clin. Immunol. Immunopathol. 51, 338-347). Thus, the results solved the question of why the IgG3 was co-present with deposited IgA1 in IgA nephropathy patients.

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