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Demonstration of an outer membrane protein with antiphagocytic activity from Pasteurella multocida of avian origin
1Department of Veterinary Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis 95616.
Abstract:
A strain of Pasteurella multocida of avian origin was found to inhibit phagocytosis of Candida albicans by mononuclear phagocytes in vitro. Whole-cell lysates of P. multocida showed this effect, as did a 50-kilodalton (kDa) protein eluted from sodium dodecyl sulfate-polyacrylamide gels obtained by electrophoresis of whole-cell lysates. Heat, digestion with trypsin, and antibody specific for this 50-kDa protein neutralized the antiphagocytic effects of P. multocida, of the whole-cell lysates, and of the 50-kDa protein itself. Evidence that this protein was in the outer membrane of the bacterial cell included the findings that (i) treatment of encapsulated or unencapsulated P. multocida with trypsin reduced the antiphagocytic effect; (ii) whole-cell lysates prepared from trypsinized, unencapsulated P. multocida had reduced antiphagocytic activity; and (iii) antibody to outer membrane proteins neutralized the antiphagocytic effect. Turkeys given antibodies specific for the 50-kDa outer membrane protein were protected against lethal challenge with P. multocida.
Insights
A specific protein from Pasteurella multocida inhibits the immune system's ability to engulf Candida albicans. Antibodies targeting this bacterial protein protect turkeys from infection.
Area of Science:
- Immunology
- Microbiology
- Bacteriology
Background:
- Phagocytosis is a key immune process where cells engulf pathogens.
- Certain bacterial components can interfere with host immune responses.
- Pasteurella multocida is an avian pathogen with potential immune-evasive mechanisms.
Purpose of the Study:
- To identify the specific component of Pasteurella multocida responsible for inhibiting phagocytosis.
- To characterize the nature and location of this antiphagocytic factor.
- To evaluate the potential of targeting this factor for therapeutic intervention.
Main Methods:
- In vitro assays using mononuclear phagocytes and Candida albicans.
- Isolation and purification of bacterial proteins via electrophoresis.
- Treatment of bacterial components with heat, trypsin, and specific antibodies.
- In vivo challenge studies in turkeys.
Main Results:
- A 50-kilodalton (kDa) protein from P. multocida inhibited phagocytosis of Candida albicans.
- This protein was localized to the bacterial outer membrane.
- Antibodies against the 50-kDa protein neutralized its antiphagocytic activity.
- Passive immunization with these antibodies protected turkeys against P. multocida challenge.
Conclusions:
- A 50-kDa outer membrane protein of Pasteurella multocida possesses antiphagocytic properties.
- This protein represents a potential virulence factor and a target for vaccine development.
- Antibody-mediated neutralization of this protein confers protection against avian pasteurellosis.