LOCAL AND SYSTEMIC COMPLEMENT ACTIVITY IN SMALL-INTESTINAL BACTERIAL OVERGROWTH

It is unknown whether bacteriolysis due to luminal complement activati on contributes to local defense mechanisms against small intestinal ba cterial overgrowth, particularly with gramnegative bacteria. This stud y addressed this issue. Thirty adult subjects were investigated with c ulture of luminal secretions adherent to proximal small intestinal muc osa. Luminal and plasma concentrations of C3 and C3d and C3d/C3 ratios were determined. Activated terminal complement complex was sought in surface epithelium to which aspirated secretions had been adherent. Sm all intestinal bacterial overgrowth with gram-negative bacteria was pr esent in 12/30 (40.0%) subjects. C3, C3d, and C3d/C3 profiles indicate d that increased local but not systemic C3 activation occurs in this g roup. Conversely, no activation of terminal complement complex was evi dent in this circumstance. Thus, complement-mediated bacteriolysis is unlike to contribute to local defense mechanisms against small intesti nal bacterial overgrowth, even when overgrowth flora includes gram-neg ative bacteria. Factors preventing full local activation of the comple ment cascade in this circumstance require investigation.