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Complement activation by Proteus mirabilis negatively charged lipopolysaccharides
W Kaca1, E Literacka, A G Sjöholm
1Karolinska Institutet, Division of Clinical Bacteriology, Huddinge University Hospital, Sweden. wkaca@wirus.cmiwpan.lodz.pl
Abstract:
Proteus mirabilis strains are human pathogens responsible for urinary tract infections and bacteremias and may be involved in rheumatoid arthritis. Lipopolysaccharide (LPS, bacterial endotoxin), the major component of the cell wall, is one of the virulence factors of Proteus. In the presented studies, we have investigated complement activation by LPSs isolated from P. mirabilis O10, O23, O30, and O43 strains, which differ in the number of negative COO- groups on their polysaccharide components. Four P. mirabilis strains studied were sensitive to complement-mediated killing, despite complement binding by their LPSs. The optimal complement binding by LPSs was detected in serum with functional assays for both the classical and alternative pathways. Complement activation in 80% serum by the smooth, uronic acid, and hexosamine containing P. mirabilis LPSs was not critically determined by the structure of their O-chain polysaccharides. One of four LPSs used as a model, P. mirabilis O10 LPS, fragmented C3 in an LPS dose- and time-dependent manner. It was detected by crossed-immunoelectrophoresis and capture ELISA with anti-C3c antibodies. The lower complement activation by 023 LPS correlates with its reduced C3 fragmentation, compared with three other Proteus LPSs studied. Rabbit anti-O antibodies enhanced the complement binding and factor C3 fragmentation by O10, O23, O30, and O43 P. mirabilis LPSs.
Insights
Proteus mirabilis lipopolysaccharides (LPS) activate complement pathways, but strains remain susceptible to complement-mediated killing. Antibody enhancement of LPS complement binding and C3 fragmentation was observed.
Area of Science:
- Immunology
- Microbiology
- Bacterial Pathogenesis
Background:
- Proteus mirabilis is a significant human pathogen causing urinary tract infections and bacteremia.
- Lipopolysaccharide (LPS), a key component of the bacterial cell wall, is a crucial virulence factor for Proteus species.
- The role of LPS structure in complement activation and bacterial virulence is an area of active research.
Purpose of the Study:
- To investigate the complement activation properties of lipopolysaccharides (LPS) from various Proteus mirabilis strains (O10, O23, O30, O43).
- To determine the influence of LPS structure, specifically the number of negative COO- groups, on complement binding and activation.
- To explore the impact of anti-O antibodies on LPS-mediated complement activation.
Main Methods:
- Isolation of LPS from four P. mirabilis strains.
- Functional assays to assess complement binding and activation via classical and alternative pathways in human serum.
- Quantification of C3 fragmentation using crossed-immunoelectrophoresis and capture ELISA with anti-C3c antibodies.
- Evaluation of complement activation in the presence of rabbit anti-O antibodies.
Main Results:
- All four P. mirabilis LPSs bound complement, yet the strains remained sensitive to complement-mediated killing.
- Optimal complement binding and activation occurred in 80% serum, involving both classical and alternative pathways.
- Complement activation was not critically dependent on O-chain polysaccharide structure.
- P. mirabilis O10 LPS demonstrated dose- and time-dependent C3 fragmentation, with lower activation observed for O23 LPS.
- Rabbit anti-O antibodies significantly enhanced LPS-mediated complement binding and C3 fragmentation.
Conclusions:
- Proteus mirabilis LPS can activate complement, but this does not confer resistance to complement-mediated killing.
- The structure of O-chain polysaccharides has a limited impact on complement activation by these LPS.
- Antibody responses can significantly boost the complement-activating potential of P. mirabilis LPS, potentially influencing bacterial clearance.