LUMINAL IMMUNITY IN SMALL-INTESTINAL BACTERIAL OVERGROWTH AND OLD-AGE

Background: The independent influences of small-intestinal bacterial o vergrowth and old age on mucosal immunoglobulin production and secreti on have not been assessed. This is an important issue, since luminal I gA deficiency may exacerbate small-intestinal bacterial overgrowth, th e prevalence of which is high in selected elderly populations. Methods : Proximal small-intestinal aspirates were obtained from 33 subjects f or bacteriologic analysis and measurement of total IgA, IgM, total IgG , IgG subclass, and IgD concentrations. IgA subclasses were measured i n 24 unselected subjects. Serum immunoglobulin and salivary IgA concen trations were measured in all subjects. Results: IgA2 and IgG3 were pr edominant IgA and IgG subclasses in proximal small-intestinal luminal secretions. Luminal concentrations of IgA2 and IgM, but not IgG3 or an y other IgG subclass, were significantly increased in small-intestinal bacterial overgrowth, which was present in 19 of 33 (57.6%) subjects. Old age did not influence these levels. Luminal immunoglobulin concen trations did not correlate significantly with either serum or salivary values. IgD was not measureable in proximal small-intestinal secretio ns. Conclusions: Increased luminal concentrations of the secretory imm unoglobulins, IgA2 and IgM, occur in small-intestinal bacterial overgr owth. Local investigation is mandatory when assessing the mucosal immu nopathology of this disorder. Luminal IgG3 is unlikely to be predomina ntly derived from serum. Old age does not independently influence lumi nal immunity.