Anti-capsular antibodies activate killing of Escherichia coli O8:K87 by the alternate complement pathway in porcine serum.
Enterotoxigenic Escherichia coli (ETEC) strains that produce K88 (F4)+ fimbria are important causes of diarrhea and post-diarrheal septicemia in swine. ETEC O8:K87, a serotype represented by a number of these strains, is typically serum resistant. Strain-specific antibodies are known to activate alternative C pathway-mediated killing of other serum-resistant E. coli [Hill, A.W., Shears, A.L., Hibbitt, K.G., 1978. The requirement of specific antibody for the killing of E. coli by the alternate complement pathway in bovine serum. Immunology 34, 131-136], but their antigenic targets have not been determined. We tested the hypothesis that anti-K87 antibodies activate alternative pathway-mediated killing of ETEC O8:K87. Pigs were immunized with ETEC O8:K87 strain 2534-86 cells or purified K87 polysaccharide. Post-, but not pre-immunization sera killed 2534-86 cells, and absorption with 2534-86 cells or by K87 affinity chromatography eliminated bactericidal activity. Complementation of absorbed serum with anti-K87 antibodies restored bactericidal activity, confirming the ability of these antibodies to activate C-mediated serum killing. Serum from age-matched, non-vaccinated control pigs also killed 2534-86. This activity was eliminated by absorption with 2534-86 cells, but not K87 affinity chromatography, indicating that specific non-capsular antibodies are also able to activate C-mediated killing. In all cases, Mg-EGTA-treated serum was as effective as non-treated serum in killing, suggesting that bactericidal activity was mediated predominantly if not exclusively via the alternative C pathway.
Clark
N M
NM
Department of Veterinary and Biomedical Sciences, University of Nebraska-Lincoln, Fair Street and East Campus Loop, Lincoln, NE 68583-0905, USA.
Berberov
E M
EM
Wang
M
M
Moxley
R A
RA
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D016667:Bacterial Capsules / Q000276:immunology*; D003170:Complement Pathway, Alternative / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D004926:Escherichia coli / Q000276:immunology*; D004927:Escherichia coli Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D005260:Female; D007106:Immune Sera / Q000276:immunology; D007114:Immunization / Q000379:methods / Q000662:veterinary; D051379:Mice; D008807:Mice, Inbred BALB C; D011817:Rabbits; D013047:Specific Pathogen-Free Organisms; D013552:Swine / Q000276:immunology*; D013553:Swine Diseases / Q000276:immunology* / Q000382:microbiology*
D000907:Antibodies, Bacterial; D007106:Immune Sera