Intestinal Microflora of Immunoglobulin-Deficient and Normal Human Subjects

Abstract

Population levels of indigenous microorganisms in the small intestine and feces, and titers of certain antibacterial antibodies in intestinal fluids and sera, were compared in normal and immunoglobulindeficient individuals (9 selectively IgA-deficient subjects, 3 hypogammaglobulinemic subjects, and 12 healthy subjects). Fluids were taken under nitrogen from several levels of the small bowel, and were rigorously protected from exposure to air until cultures for anaerobic bacteria were made. Antibodies were detected by their ability to flocculate bentonite particles coated with lipopolysaccharide antigens extracted from an Escherichia coli stain, Bacteroides species, or a Lactobacillus species. The IgA-deficient and control subjects had generally similar microbial populations in their feces and small bowel fluids, although 2 of the patients yielded somewhat excessive numbers of anaerobic bacteria from their upper small bowels. In contrast, moderately to greatly excessive numbers of anaerobic bacteria were cultured from the bowel fluids of all 3 hypogammaglobulinemic patients. Titers of the flocculating antibodies were normal in the 1gA-deficient patients, but much below normal in the hypogammaglobulinemic persons. All of the IgA-deficient patients had extremely low levels of IgA in their sera, and all except 1 had undetectable levels in secretions. The 3 hypogammaglobulinemic patients had low or undetectable levels of immunoglobulins in sera and secretions. Although antibodies may be involved in the complex process of regulating the small bowel microbial flora, deficiency of IgA alone is insufficient to allow serious derangement of the flora.