Radioimmunologic measurements of naturally occurring bacterial antibodies. I. Human serum antibodies reactive with Escherichia coli in gastrointestinal and immunologic disorders.

Abstract

Abstract A radioimmunologic method for quantitative measurement of naturally occurring human serum antibodies reactive with Escherichia coli was developed. The primary binding of IgG, IgA, and IgM to a nonenteropathogenic strain of E. coli was estimated from measurements of radiolabeled rabbit antihuman immunoglobulins bound to bacteria which had been incubated in human serum or purified immunoglobulins. As little as 5 ng. antibody nitrogen could be measured, and no significant interference was encouraged from crossreacting antibodies to Bacterioides fragilis , an Enterococcus species, or human erythrocytes. Anti- E. coli antibodies were measured in sera of 11 healthy subjects and 72 patients with immunologic or gastrointestinal disorders. IgM and IgG antibodies predominated quantitatively over IgA antibodies; antibody concentrations were normal in many gastrointestinal conditions in which elevations might have been expected (nontropical sprue, regional enteritis, intestinal bacterial overgrowth, and chronic liver diseases); IgG antibodies were undetectable in sera of 3 of 8 patients with chronic ulcerative colitis, the only patients in the entire series except for those with hypogammaglobulinemia in whom this was observed; IgG antibody concentrations were 2 to 17 times above the maximum normal control value in 4 of 10 patients selectively deficient in IgA; and IgA-class antibodies were below measurable levels in all 20 IgA myeloma sera.