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Biological Sciences

Pathogenicity Genotype Versus Phenotype

Sponsor: National Institute of Allergy and Infectious Disease
Contact: Josh Adkins

Closely related pathogens such as distinct sub-species of Salmonella (typhimurium, typhi, and arizona) and related orthopoxviruses (variola major, vaccinia, and monkeypox) vary substantially in virulence. Even within the same species, many mutant strains are totally avirulent in immunocompetent individuals. Although the precise genetic defect is known for many strains of decreased virulence, the consequences of even well-defined mutations by the pathogen on other proteins, in particular major intracellular regulatory proteins, is unknown. Using Salmonella as a model bacterial system, we hypothesize that a subset of the proteins differentially expressed in wild-type vs. mutant strains of Salmonella are mechanistically involved in pathogenicity and thus could be novel therapeutic targets. We also hypothesize that proteins differentially expressed in wild-type monkeypox, in comparison to vaccinia or an avirulent mutant strain of monkeypox, contribute mechanistically to the differing virulence of these viruses in human hosts.

These hypotheses form the rationale for a pair of proteomic studies designed to compare highly virulent to less virulent pathogens. The first study aims to characterize different Salmonella strains grown in distinct host-cell types, while the second study seeks to characterize orthopox virus strains grown in epithelial cells and macrophages. An example of the results we expect to attain is a comparison of the S. typhimurium proteome expressed within mouse macrophages to that of a mutant strain that is missing a specific genetic regulator. These results can provide insight into the cascade of proteins that are involved in intracellular replication and virulence. We expect that a significant number of differentially expressed proteins, many of which may not be obviously related to pathogenesis, will be identified in these comparative studies of virulent and avirulent proteomes. While similar comparisons of expressed proteins from the same strain cultured in different cell types will also reveal differences, only a subset of these differences are expected to contribute directly to pathogenesis.

Obtaining specific information about the timing of expression, particularly in relation to the timing of intracellular replication, provides important information regarding those gene products that are most essential for intracellular replication. On the basis of this assumption, we plan to use bioinformatics to select proteins that are associated with virulence and are correspondingly altered in non-productive infections for further validation. The results from additional parallel studies with orthopoxviruses of differing pathogenicity in epithelial cells and macrophages will provide a useful comparison of differences in the host response to bacterial vs. viral infections.

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