Artikel
The structure of the cell wall polysaccharide of Enterococcus faecalis is critical for evasion of complement deposition by the lectin pathway
Die Struktur des Zellwandpolysacchrids von Enterococcus faecalis vermittelt die Resistenz gegen Komplementaktivierung durch den Lektin-Weg
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Autoren
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C. Theilacker
- University Hospital Freiburg, Center for Infectious Diseases & Travel Medicine, and IFB-Center for Chronic Immunodeficiency, Freiburg, Germany
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S. Geiss
- University Hospital Freiburg, Center for Infectious Diseases & Travel Medicine, and IFB-Center for Chronic Immunodeficiency, Freiburg, Germany
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J. Hübner
- University Hospital Freiburg, Center for Infectious Diseases & Travel Medicine, and IFB-Center for Chronic Immunodeficiency, Freiburg, Germany
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J.A. van Strijp
- University Medical Center Utrecht, Department of Medical Microbiology, Utrecht, Netherlands
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S. Rooijakkers
- University Medical Center Utrecht, Department of Medical Microbiology, Utrecht, Netherlands
| Veröffentlicht: | 2. Juni 2010 |
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Gliederung
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Introduction: Enterococcus faecalis is a Gram-positive pathogen that may cause invasive infections in immunocompromised patients. E. faecalis is resistant to serum but the molecular mechanism underlying complement evasion is not known. We have generated an insertion mutant of the putative glycosyltransferase EF1172 in E. faecalis strain V583 that expresses a structurally altered cell-wall polysaccharide (see companion abstract by Geiss et al. “Role of enterococcal cell wall polysaccharide structure in resistance to killing by neutrophils“). The mechanism of increased complement susceptibility in the mutant strain was investigated.
Methods: Complement deposition and phagocytosis was quantified by FACS. Killing of enterococci in the presence of serum and PMNs was measured using an opsonophagocytic killing assay. Human pooled serum was preabsorbed with live wild-type E. faecalis V583 for all assays.
Results: Incubation of E. faecalis V583Δ1172 with 1.5% serum and PMNs for 90 min reduced the number of viable bacteria by >2 logs, while wild type bacteria were resistant to killing under these experimental conditions. After 15 min incubation of live bacteria preopsonized with 0,6 - 5% human pooled serum (HPS), PMNs phagocytosed fivefold more E. faecalis V583Δ1172 than wild type bacteria. Also, significantly more C3b was deposited on V583Δ1172 compared to the wild type strain. Chelation of Ca++ as a cofactor of the classical and lectin pathway reduced C3b deposition on V583Δ1172 below wild type levels while significantly more C3b was deposited on V583Δ1172 by serum depleted of complement factor C1q, indicating that classical and alternative pathway of complement activation are not involved in the reduced complement resistance the mutant strain. Furthermore, V583Δ1172 incubation with HPS lead to more binding of C4b – a component of the C3 convertase generated by the classical and lectin pathway – than wild type cells. The role of the lectin pathway in increased susceptibility to complement was confirmed by elevated levels of mannose binding lectin-associated serum protease 2 (MASP-2) bound to the mutant strain.
Conclusion: The structure of the wall polysaccharide of E. faecalis is critical to resistance to complement activation by the lectin pathway. Further studies need to address the molecular interaction between lectins and the cell wall polysaccharide.
