Distribution of virus antibody activity among human IgG subclasses

Human IgG subclass antibody activity against viruses was studied by separating the IgG3 fractions from sera exhibiting high titres for rubella, polio types I, II and III, and herpes I viruses. The sera were fractionated on DEAE Affi-Gel Blue and protein A-Sepharose CL-4B columns using specific subclass antisera for identification. All IgG3 fractions exhibited a molecular weight of 164,000 daltons, a pI mean of 8.21 and S20,W1% = 6.2 as determined by polyacrylamide gel electrophoresis, isoelectric focusing and analytical centrifugation. Quantitative determination of the individual subclass concentrations by nephelometry showed them to be within the biological norm. The concentration and distribution of IgG in the sera and that of the IgGl, -2 and -4 and IgG3 fractions were used as a basis for studying antiviral activity. The IgG3 fractions showed a greater ratio of IgG concentration to antibody titre than the IgGl, -2 and -4 fractions as determined in neutralization and haemagglutination inhibition tests. The IgG3 fraction from anti-rubella serum bound 96.6% 125I-labelled rubella virus (HP 77/DE5). The IgG 3-125I-rubella immune complex was separated over a protein A-Sepharose CL-4B column and confirmed with subclass-specific antisera in radial immunodiffusion plates. Individual Gm allotype analyses showed markers distributed as follows: G3m(5,-6,10,11,13,-16,21,-24) for all the serum donors indicating similar genotypic expression of IgG3s.