Competition Between, and Effectiveness of, IgG and IgM Antibodies in Indirect Fluorescent Antibody and Other Tests

Abstract

Natural human 19S (IgM) and 7S (IgG) antibodies reactive with Neisseria gonorrhoeae were assayed by agglutination, bactericidal and indirect fluorescent antibody (IFA) procedures. Fluorescent antibody reagents specific for IgG and IgM were used in the IFA procedure. It was found that purified 19S serum fractions contained antibodies which were readily detected by agglutination, bactericidal and IFA techniques using an anti-IgM reagent. However, bactericidal and agglutination tests appeared to be relatively insensitive to natural IgG antibodies in purified 7S fractions. In contrast, the indirect fluorescent antibody technique using an anti-IgG reagent could detect high titers of IgG antibodies within the 7S fractions. A prozone phenomenon was observed in the IFA reactivity of IgM antibodies in whole serum. It was found that the addition of purified 7S antibodies to purified 19S antibody fractions decreased the ability of the 19S fraction to react with the anti-IgM reagent. This suggested that IgG antibodies inhibited IgM antibody reactivity in the IFA procedure. A partial inhibition of 19S bactericidal activity by 7S fractions was also found. This study indicates that the unequal capacity of different antibody classes to produce reactions, and the interactions between antibodies themselves in various test systems, must be taken into account in the interpretation of the results of immunologic tests.