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High-molecular-weight surface-exposed proteins of Haemophilus influenzae mediate binding to macrophages
G J Noel1, S J Barenkamp, J W St Geme
1Division of Pediatric Infectious Diseases and Immunology, Cornell University Medical College, New York, New York.
Abstract:
The molecular basis for direct bacteria-macrophage interactions that distinguishes nontypeable (NT) Haemophilus influenzae from type b organisms is not known. Because of similarities between filamentous hemagglutinin (FHA) adhesin of Bordetella pertussis and high-molecular-weight (HMW) proteins commonly expressed by NT H. influenzae, the role that HMW proteins play in determining NT H. influenzae-macrophage interactions was assessed. In tests with genetically engineered organisms, HMW protein-expressing bacteria bound significantly better than isogenic HMW protein-deficient bacteria to macrophages. HMW protein-dependent binding to macrophages is trypsin-sensitive, is independent of divalent cations, does not occur via the leukocyte integrin CD11b/CD18, and is not affected by galactose-containing carbohydrates. Organisms bound via HMW proteins remain largely extracellular and viable. Like FHA of Bordetella organisms, HMW proteins mediate binding of NT H. influenzae to macrophages. However, unlike the interaction determined by FHA, this interaction is characteristically one of adhesion and requires additional serum opsonization for efficient killing of bacteria by macrophages.
Insights
High-molecular-weight (HMW) proteins on nontypeable Haemophilus influenzae mediate bacterial adhesion to macrophages. This interaction, distinct from type b strains, requires serum for effective bacterial clearance.
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Nontypeable (NT) Haemophilus influenzae interactions with macrophages are not fully understood.
- Similarities exist between Bordetella pertussis filamentous hemagglutinin (FHA) and NT H. influenzae high-molecular-weight (HMW) proteins.
Purpose of the Study:
- To investigate the role of HMW proteins in NT H. influenzae binding to macrophages.
- To elucidate the molecular mechanisms underlying this interaction.
Main Methods:
- Utilized genetically engineered NT H. influenzae strains with and without HMW protein expression.
- Assessed bacterial binding to macrophages using various assays, including trypsin sensitivity and cation dependence.
- Investigated the role of CD11b/CD18 and galactose-containing carbohydrates.
Main Results:
- HMW protein-expressing NT H. influenzae exhibited significantly enhanced binding to macrophages compared to HMW-deficient strains.
- HMW protein-dependent binding was trypsin-sensitive, cation-independent, and did not involve CD11b/CD18 or galactose.
- Bound bacteria remained largely extracellular and viable, indicating adhesion rather than invasion.
Conclusions:
- HMW proteins are key mediators of NT H. influenzae adhesion to macrophages, similar to FHA in B. pertussis.
- This adhesion mechanism differs from FHA-mediated interactions and necessitates serum opsonization for efficient bacterial killing by macrophages.