title: Local and systemic complement activity in small intestinal bacterial overgrowth.
abstract: It is unknown whether bacteriolysis due to luminal complement activation contributes to local defense mechanisms against small intestinal bacterial overgrowth, particularly with gram-negative bacteria. This study addressed this issue. Thirty adult subjects were investigated with culture of luminal secretions adherent to proximal small intestinal mucosa. 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. Small intestinal bacterial overgrowth with gram-negative bacteria was present in 12/30 (40.0%) subjects. C3, C3d, and C3d/C3 profile indicated that increased local but not systemic C3 activation occurs in this group. Conversely, no activation of terminal complement complex was evident in this circumstance. Thus, complement-mediated bacteriolysis is unlike to contribute to local defense mechanisms against small intestinal bacterial overgrowth, even when overgrowth flora includes gram-negative bacteria. Factors preventing full local activation of the complement cascade in this circumstance require investigation.
authors.affiliation: Department of Gastroenterology, Prince of Wales Hospital, Sydney, Australia.
authors.forename: S M
authors.initials: SM
authors.lastname: Riordan
authors.forename: C J
authors.initials: CJ
authors.lastname: McIver
authors.forename: D
authors.initials: D
authors.lastname: Wakefield
authors.forename: P C
authors.initials: PC
authors.lastname: Andreopoulos
authors.forename: V M
authors.initials: VM
authors.lastname: Duncombe
authors.forename: T D
authors.initials: TD
authors.lastname: Bolin
authors.forename: M C
authors.initials: MC
authors.lastname: Thomas
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D015984:Causality; D003167:Complement Activation; D003176:Complement C3 / Q000276:immunology*; D015933:Complement C3d / Q000276:immunology*; D016905:Gram-Negative Bacterial Infections / Q000276:immunology* / Q000382:microbiology; D016908:Gram-Positive Bacterial Infections / Q000276:immunology* / Q000382:microbiology; D006801:Humans; D007410:Intestinal Diseases / Q000276:immunology* / Q000382:microbiology; D007413:Intestinal Mucosa / Q000276:immunology / Q000382:microbiology; D007419:Intestinal Secretions / Q000276:immunology / Q000382:microbiology; D007421:Intestine, Small / Q000276:immunology / Q000382:microbiology*; D008875:Middle Aged
chemical_list: D003176:Complement C3; D015933:Complement C3d