Genetic basis of susceptibility to invasive pneumococcal disease

Lead Research Organisation: University of Leicester
Department Name: Infection Immunity and Inflammation


Streptococcus pneumoniae (the pneumococcus) is one of the most common infectious agents of humans and every year the bacterium causes illness and death in millions of individuals but the genetic basis of susceptibility to the bacterium is unknown. Previous attempts to directly identify in humans the gene explaining differing susceptibility to pneumococcal disease have been without significant success. In order to develop new hypotheses that can be tested in humans, in this project we will exploit the possibilities offered by using animals.
Previously we showed that different mouse strains vary in susceptibility to S. pneumoniae and identified part of the mouse chromosome 7, containing about 200 genes, as the location of a gene that determines susceptibility. This region of the mouse chromosome is very similar to part of a human chromosome. This project aims to identify the key mouse gene and to investigate how the gene influences the development of pneumococcal disease.
The project will use a programme of mouse breeding known as speed congenics, to narrow the ?susceptibility region? to about 10 genes. Each gene within the narrowed region will be assessed by comparison of its DNA sequence in susceptible and resistant mouse strains and by comparison of the expression of the genes in the tissues of these mice. The resulting hypothesis on which gene is the cause of susceptibility will be tested by determining how resistance and pathology is changed when we replace the candidate gene in the resistant strain with the gene from the susceptible strain. Identification of the candidate gene will increase our understanding of pneumococcal disease and will provide plausible candidates for future studies in humans and could lead to new drug targets and therapeutic approaches therapy.
We are committed to better public awareness of research issues through involvement with industry, healthcare providers, patient associations and the general public. Our press office has effective contacts with the media and on several occasions the media have interviewed us about pneumococcal disease and research issues. We present ourselves to the public via open days, public lectures and presentations to alumni. We have a policy of sharing results with external parties, after consideration of IPR. Therefore we will have a web-based database of findings and produce technical dossiers to explain results to different stakeholders including industry. We are committed to the publication of the project results in prestigious journals and at presentations at scientific and medical conferences.

Technical Summary

The objectives are to: [1] identify a candidate gene that is a basis for variation in susceptibility to invasive pneumococcal disease, [2] determine the causative mutation within the identified gene or its promoter, [3] investigate predictions of how the gene influences the pathogenesis of pneumonia.
The foundation of this proposal is our identification of mouse strains susceptible or resistant to pneumococcal disease and discovery of a single major linkage with survival and bacteraemia on an 8cM region of chromosome 7 of the mouse.
The flow of the work will be:
1:Speed congenics to narrow the region to less than 1cM (5-10 genes). The phenotype of the mice will be measured by the disease signs and extent of bacteraemia following intranasal infection.
2. Candidates within the 1cM region will be assessed by comparison of the nucleotide sequences of the genes and their promoters in the susceptible and resistant strains and by comparison of the transcript profiles in the lungs and bone marrow of the congenic mice.
3. The resulting hypothesis of which gene is the cause of susceptibility or resistance will be tested by determining how resistance is changed when the candidate gene in the resistant strain is replaced by the gene from the susceptible strain.
4. The strains of mice that will result will be used to define more clearly than can be done with the parent strains, how the causative gene influences the pathogenesis of pneumococcal disease.


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