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A large, antigenically conserved protein on the surface of Moraxella catarrhalis is a target for protective
M E Helminen1, I Maciver, J L Latimer
1Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235-9048.
Abstract:
A monoclonal antibody (MAb) to Moraxella catarrhalis O35E bound to a surface-exposed epitope of a proteinaceous antigen of this organism. The antigen, designated UspA, was present in every strain of the pathogen tested in a colony blot RIA. UspA had a molecular mass on SDS-PAGE that varied between 300 and 400 kDa, depending on the individual M. catarrhalis strain. Passive immunization of mice with the UspA-reactive Mab enhanced pulmonary clearance of M. catarrhalis. Use of this Mab to screen a M. catarrhalis genomic DNA library permitted identification of a recombinant bacteriophage expressing the M. catarrhalis UspA protein. The recombinant UspA protein was used in Western blot analysis with sera from patients with M. catarrhalis pneumonia. Convalescent-phase sera but not acute-phase sera from these patients contained antibodies to this M. catarrhalis surface protein, indicating that M. catarrhalis strains growing in vivo express this molecule.
Insights
A novel surface protein, UspA, from Moraxella catarrhalis was identified. Antibodies against UspA enhanced bacterial clearance in mice, suggesting its potential as a vaccine target.
Area of Science:
- Microbiology
- Immunology
- Bacteriology
Background:
- Moraxella catarrhalis is a significant human pathogen.
- Surface antigens are crucial for bacterial virulence and host immune response.
Purpose of the Study:
- To identify and characterize surface antigens of Moraxella catarrhalis.
- To evaluate the immunogenic potential of a novel surface protein, UspA.
Main Methods:
- Monoclonal antibody production and characterization.
- Colony blot radioimmunoassay (RIA) and SDS-PAGE for antigen detection and molecular mass determination.
- Passive immunization studies in mice.
- Screening of a genomic DNA library and recombinant protein expression.
- Western blot analysis using patient sera.
Main Results:
- A surface-exposed protein antigen, UspA, was identified in all Moraxella catarrhalis strains tested.
- UspA molecular mass varied from 300 to 400 kDa.
- Passive immunization with UspA-reactive monoclonal antibody enhanced pulmonary clearance of M. catarrhalis in mice.
- Recombinant UspA elicited antibody response in convalescent-phase sera from patients with M. catarrhalis pneumonia.
Conclusions:
- UspA is a conserved surface protein of Moraxella catarrhalis.
- UspA is expressed during in vivo infection.
- UspA is a potential target for vaccine development against Moraxella catarrhalis infections.