INTERLEUKIN-6 AND SMALL-INTESTINAL LUMINAL IMMUNOGLOBULINS

Our aim was to determine the relationships between interleukin-6 and i mmunoglobulin levels within small intestinal luminal secretions. Twent y adult subjects with small intestinal bacterial overgrowth (N = 13), irritable bowel syndrome (N = 4), and nonulcer dyspepsia (N = 3) under went endoscopic aspiration of secretions from the small intestinal muc osal surface for assessment of IL-6, IgA(1), IgA(2), IgM, IgG(1), IgG( 2), IgG(3), and IgG(4) concentrations. Serum immunoglobulin concentrat ions and small intestinal histology were also determined. IgA(2) and I gG(3) were the predominant IgA and IgG subclasses in luminal secretion s in 19/20 (95%) and 20/20 (100%) subjects, respectively. IgA(1) and I gG(1) predominated in serum in all subjects. No subject had villous at rophy. Luminal IL-6 concentrations correlated significantly with lumin al IgA(2), IgM, and IgG(3) concentrations but not with IgA(1) or any o ther IgG subclass levels. Conversely, luminal IL-6 or immunoglobulin c oncentrations did not correlate significantly with levels of any immun oglobulin isotype in serum. These observations suggest that important relationships exist between local IL-6 and IgA(2), IgM, and IgG(3) res ponses in human small intestinal luminal secretions. Local investigati on is mandatory when assessing intestinal immune activity.