Response and specificity of antibodies for Shigella flexneri: demonstration of type-specific factors in immunoglobulin G fraction of antiserum.

Considerable amounts of immunoglobulin G (IgG) antibody appeared in hyperimmune rabbit serum at a late period during a course of immunization with several injections of Shigella flexneri O antigens. High yields of IgG antibody possessing homogenous specificity could be fractionated from crude gamma-globulin solution on a diethylaminoethyl-Sephadex column with 0.02 m phosphate buffer (pH 6.6) containing 0.1 m NaCl. Specificities of IgG antibodies for six serotypes of S. flexneri were demonstrated to be high as compared with those of whole sera and their IgM antibodies. Type-specific factors for antigens I to VI were shown in each IgG fraction according to serotype employed. Further, in most sera, subtype-specific factors could be detected in the IgG fraction. These results suggest that it would be desirable to use IgG antibodies for the typing of S. flexneri.