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Binding of mannan-binding protein to various bacterial pathogens of meningitis
L C van Emmerik1, E J Kuijper, C A Fijen
1Department of Medical Microbiology, University of Amsterdam, The Netherlands.
Abstract:
Mannan-binding protein (MBP), a calcium-dependent plasma lectin, may play a role in the innate defence against microorganisms. After binding to carbohydrate structures at the bacterial surface, MBP activates the classical pathway of the complement system. To investigate the binding capacity of MBP to various bacteria associated with meningitis, an assay was developed to study the binding of MBP to bacteria grown in a semisynthetic fluid culture medium. Salmonella montevideo (containing a mannose-rich lipopolysaccharide (LPS)), used as a positive control strain, showed binding of radiolabelled MBP at a level of 80% compared with binding of MBP to zymosan. Binding of labelled MBP to Salm. montevideo was time-dependent, temperature-dependent and saturable. The binding was inhibited by unlabelled MBP, by mannose and by N-acetyl-D-glucosamine. Among bacterial pathogens often found to cause meningitis, a wide range of MBP binding capacities could be determined. The encapsulated Neisseria meningitidis (representatives from 11 serogroups other than group A were included: n = 22), N. mucosa (n = 1), Haemophilus influenzae type b (n = 10) and Streptococcus agalactiae (n = 5) had a low MBP binding capacity of 21.7% (95% confidence interval (CI) 3.3-40.1%). Escherichia coli K1 (n = 11), Strep. suis (n = 5), Strep. pneumoniae (n = 10) and N. meningitidis serogroup A (n = 2) showed intermediate MBP binding capacity of 58.4% (95% CI 40.0-76.8%). A third group consisting of non-encapsulated Listeria monocytogenes (n = 11), non-encapsulated H. influenzae (n = 2), non-encapsulated N. meningitidis (n = 2), N. cinera (n = 1) and N. subflava (n = 1) strains had a high MBP binding capacity of 87.5% (95% CI 62.5-112.5%). The majority of encapsulated pathogens causing bacterial meningitis seem to have a rather low MBP binding capacity.
Insights
Mannan-binding protein (MBP) binding varies among meningitis-causing bacteria. Encapsulated strains generally show low binding, while non-encapsulated strains exhibit high binding, impacting innate immunity against bacterial meningitis.
Area of Science:
- Immunology
- Microbiology
- Infectious Diseases
Background:
- Mannan-binding protein (MBP) is a calcium-dependent plasma lectin involved in innate immune defense against microorganisms.
- MBP activates the classical complement pathway upon binding to carbohydrate structures on bacterial surfaces.
Purpose of the Study:
- To investigate the binding capacity of MBP to various bacteria commonly associated with meningitis.
- To develop an assay for studying MBP binding to bacteria cultured in a semisynthetic fluid medium.
Main Methods:
- Developed an assay to quantify MBP binding to bacteria.
- Utilized radiolabeled MBP and bacterial strains including Salmonella montevideo (positive control), Neisseria meningitidis, Haemophilus influenzae, Streptococcus agalactiae, Escherichia coli K1, Streptococcus suis, Streptococcus pneumoniae, and Listeria monocytogenes.
- Assessed binding in relation to encapsulation status, time, temperature, and presence of inhibitors like mannose.
Main Results:
- Salmonella montevideo showed high MBP binding (80%), which was time-dependent, temperature-dependent, saturable, and inhibited by mannose and N-acetyl-D-glucosamine.
- Encapsulated Neisseria meningitidis, Haemophilus influenzae type b, and Streptococcus agalactiae exhibited low MBP binding (21.7%).
- Escherichia coli K1, Streptococcus pneumoniae, and Neisseria meningitidis serogroup A showed intermediate binding (58.4%).
- Non-encapsulated Listeria monocytogenes, Haemophilus influenzae, and Neisseria meningitidis strains demonstrated high MBP binding (87.5%).
Conclusions:
- MBP binding capacity varies significantly among bacterial meningitis pathogens.
- Encapsulated bacterial pathogens causing meningitis generally display low MBP binding capacity.
- Non-encapsulated strains show high MBP binding, suggesting a differential role in innate immunity against meningitis-causing bacteria.