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Infection and Immunity, December 2001, p. 7304-7309, Vol. 69, No. 12
Institute of Theoretical
Surgery1 and Department of Anatomy and
Cell Biology,5 Philipps University Marburg,
Marburg, Germany; Department of Microbiology and Immunology,
University of Leicester, Leicester,2 and
Rheumatology Section, Hammersmith Campus, Imperial College
School of Medicine, London,3 United Kingdom;
and Department of Medical Microbiology and Immunology,
University of Århus, Århus, Denmark4
Received 28 June 2001/Returned for modification 1 August
2001/Accepted 7 September 2001
The complement system and the natural antibody repertoire provide a
critical first-line defense against infection. The binding of natural
antibodies to microbial surfaces opsonizes invading microorganisms and
activates complement via the classical pathway. Both defense systems
cooperate within the innate immune response. We studied the role of the
complement system in the host defense against experimental
polymicrobial peritonitis using mice lacking either C1q or factor B and
C2. The C1q-deficient mice lacked the classical pathway of complement
activation. The factor B- and C2-deficient mice were known to lack the
classical and alternative pathways, and we demonstrate here that these
mice also lacked the lectin pathway of complement activation. Using
inoculum doses adjusted to cause 42% mortality in the wild-type
strain, none of the mice deficient in the three activation routes of
complement (factor B and C2 deficient) survived (mortality of 100%).
Mortality in mice deficient only in the classical pathway of complement activation (C1q deficient) was 83%. Application of further dilutions of the polymicrobial inoculum showed a dose-dependent decrease of
mortality in wild-type controls, whereas no changes in mortality were
observed in the two gene-targeted strains. These results demonstrate
that the classical activation pathway is required for an effective
antimicrobial immune defense in polymicrobial peritonitis and that, in
the infection model used, the remaining antibody-independent complement
activation routes (alternative and lectin pathways) provide a
supporting line of defense to gain residual protection in classical
pathway deficiency.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.12.7304-7309.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Role of the Classical Pathway of Complement
Activation in Experimentally Induced Polymicrobial
Peritonitis

*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, University of Leicester, University Rd., Leicester LE1 9HN, United Kingdom. Phone: 0044-116-252-5674. Fax: 0044-116-252-5030. E-mail: ws5{at}le.ac.uk.
Present address: Department of Anthropology and Human Genetics,
Ludwig-Maximilian-University, Munich, Germany.
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