Immunoglobulin Class Responsible for Gonococcal Bactericidal Activity of Normal Human Sera

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Abstract
“Natural” gonococcal bactericidal antibody is present in the serum of most normal adults and may prevent the systemic dissemination of serum sensitive strains of Neisseria gonorrhoeae. The bactericidal activity of normal human serum for gonococcal strain F62 resides entirely in the IgM serum fraction and is destroyed by treatment with 2-mercaptoethanol. Its absence from cord, but not paired maternal sera, provides additional evidence that this activity is mediated by IgM. Serum bactericidal activity is low and comparable to cord serum for the first 4 weeks of life, rising progressively thereafter to 25, 50, and 100% of the adult geometric mean titer at ages 6 months, 1 year, and 2 years, respectively. The sera of eight patients with x-linked agammaglobulinemia were deficient in gonococcal bactericidal antibody. In contrast, sera from a single patient with x-linked immunodeficiency with increased IgM and nine patients with ataxia telangiectasia possessed normal bactericidal activity for strain F62. The development of gonococcal bactericidal antibody may be delayed in the Wiskott-Aldrich syndrome, since bactericidal activity was low for age in two patients studied at age 2 years, but normal in a third child studied at age 12. The magnitude and nature of the antibody response to bacteriophage antigen and the IgM serum concentration were correlated with the serum bactericidal activity of 22 patients with variable immunodeficiencies. The characterization of the natural occurrence of gonococcal bactericidal antibody should serve as a useful baseline in studies of the immune response to gonococcal infection or immunoprophylaxis.