Relative functional activity of purified human immunoglobulin G against a type III Group B streptococcal strain

Human immunoglobulin G (IgG) separated from whole serum by a quaternary aminoethyl-Sephadex A-50 ion exchanger was evaluated for its activity against a type III group B streptococcal strain in the newbown rat model. Separated IgG yielded approximately 70 to 80% of whole serum IgG and did not contain detectable IgM or IgA. This IgG preparation also also contained similar ratios of specific type III group B streptococcal antibody to total IgG in comparison with whole serum. In vivo, 50% protection from death was achieved by 3.9 ng of type III-specific antibody per 10 g of rat body weight. This value was considerably lower than 50% protective doses obtained in our previous studies with different human IgG preparations. Further studies are needed to understand the mechanism responsible for these differences in the functional activity of IgG antibody.