An Antigen-Binding Capacity Test for Human Immunoglobulin G (IgG) Fragments

[摘要] The ammonium sulfate method of Farr has been modified for the use of human immunoglobulin (IgG) Fab′ and Fc fragments. Precipitation of radiolabeled fragments bound to antibody was obtained by addition of 40% saturated ammonium sulfate (SAS). In the presence of normal serum more than 95% of both fragments were soluble in the same SAS concentration.Antigen-binding capacities (ABC) for IgG fragments in antisera to IgG were measured simultaneously by using an antigen solution containing 131I labeled Fab′ and 125I labeled Fc. Specificity of the ABC test was evaluated by incubating the antigen mixture with antisera of various specificities. Addition of unlabeled Fab′ in excess to the paired labeled fragments specifically inhibited the binding of 131I Fab′ to antibody.Comparison of binding capacities for Fab′ and Fc fragments in hyperimmune anti-IgG sera from various species showed some differences in the relative amount of antibodies against the antigenic determinants present on each fragment. However, these quantitative differences depended upon the period of immunization and the number of antigen injections. Rat antisera obtained after five injections of IgG showed similar ABC values for Fab′ and Fc, whereas 1 month after the first injection a much better response to Fc was found in that species. In comparison, ABC values for Fab′ and Fc were similar in rabbit antisera obtained at various time intervals during the course of immunization with IgG.

[学科分类] 生物科学（综合）