Determining the role of M cells in TSE agent neuroinvasion from the intestine

Transmissible spongiform encephalophathies (TSEs) are prolonged diseases which cause extensive degeneration in the brain. In the absence of a cure these diseases are invariably fatal. These diseases affect both animals and humans, and include Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy in cattle, chronic wasting disease in mule deer and elk, and scrapie in sheep and goats.

Some animal species and humans have become infected with these diseases after eating TSE agent-contaminated food, or through lesions or cuts to the skin, mucous membranes or cornea. Many questions remain concerning the route the infectious TSE agent takes from the site of exposure (eg: skin lesions) to the brain where it causes damage to nerve cells. After exposure TSE agents appear to high-jack the immune system where they replicate in it before they then spread to the brain. This replication in the immune system is crucial for TSE agents to efficiently reach the brain where they ultimately cause nerve damage and death of the host.

Our studies show that after oral infection TSE agents target the Peyer's patches within the intestine and infect specialised cells, termed follicular dendritic cells. During TSE disease the body is unable to recognise and destroy the TSE agents. Instead, the follicular dendritic cells become infected with high levels of TSE agents. Our research shows that the infection of follicular dendritic cells by TSE agents is a crucial early step in the disease process as treatments that block TSE infection of follicular dendritic cells, block disease transmission.

How TSE agents initially infect Peyer's patches and the follicular dendritic cells within them is unknown. If we can discover how TSE agents infect these sites, we may be able to design treatments that block this ability and therefore prevent infection. The lining of the intestine is designed to prevent pathogenic microorganisms infecting the host. However, within it are specialised cells termed M cells which enable the immune system to sample the gut contents and mount an immune response if necessary. While M cells are an important component of the intestinal immune system they may also be an Achilles heal as some pathogens appear to exploit them to enter the host. Indeed some pathogens such as Salmonella may use M cells as Trojan horses to enter the body. This study will test the hypothesis that TSE agents likewise exploit M cells to gain access to Peyer's patches and infect follicular dendritic cells. If we can identify the cellular route through which TSE agents infect the host it may be possible to design treatments that block disease transmission. Currently, effective therapeutics and prophylactics to treat TSE diseases are lacking. Furthermore, no reliable preclinical diagnostic test is available. Thus a thorough understanding of the early events in TSE pathogenesis will aid the determination of risk, the development of pre-clinical diagnostics and therapeutics, especially the development vaccines against TSE agents.

After oral exposure many TSE agents replicate first on follicular dendritic cells (FDC) in the gut-associated lymphoid tissues (GALT) as they spread from the site exposure (intestine) to the brain (termed, neuroinvasion). For TSE agents to replicate on FDC in the GALT after ingestion of a contaminated meal they must first cross the gut epithelium. However, the precise cellular mechanism by which TSE agents are conveyed into Peyer's patches is not known. Within the Peyer's patch epithelium are M cells, unique epithelial cells specialized for the transepithelial transport of particles. M cells are plausible sites of TSE agent transport across the gut epithelium, but definitive demonstration in vivo is lacking. This is important, as several M cell-independent mechanisms have also been proposed. A thorough understanding of the early stages of TSE pathogenesis in the GALT is crucial to determine the factors that influence the risk of infection and the identification of cellular and molecular targets for intervention. Using unique in vivo models will be used to definitively determine the role of M cells in TSE agent neuroinvasion from the intestine and test the hypothesis that M cells play a crucial role in oral TSE pathogenesis. Objective 1 tests the hypothesis that in the specific absence of M cells, TSE agent accumulation in the GALT is blocked and neuroinvasion impaired. Objective 2 aims to determine whether inflammatory stimuli that enhance M cell differentiation also enhance TSE agent uptake. Objective 3 will determine whether inflammation-mediated villous M cell expansion exacerbates TSE pathogenesis by facilitating systemic dissemination and neuroinvasion from tissues other than Peyer's patches. These data will help predict how inflammation and co-fection with gastrointestinal pathogens may influence TSE pathogenesis. This study will provide important missing data on how orally-acquired TSE agents infect the GALT during steady-state and inflammatory conditions.

Researchers in industry and in academia will benefit from data in this project describing the role of M cells in TSE agent neuroinvasion from the intesine. Data describing the role of these cells in TSE disease susceptibility will aid the design of novel therapeutics, especially mucosal vaccines.

TSE diseases have had significant economic impact on the UK farming industry. Any future outbreaks of novel TSE outbreaks are likely to have huge economical impact on the food and livestock industry. Since any novel TSE outbreaks may most likely occur via the oral exposure, the farming and animal husbandry industries (farmers, breeders etc.), and food-security policy makers will have significant interest in the project's outputs.

Immunologists will be interested in data generated from this study . This is the first study to determine whether M cells and inflammatory stimuli that influence their development likewise influence susceptibility to an important orally-acquired pathogen.

UK policy makers will have interest in the project's findings on novel factors that may influence TSE susceptibility. This may influence their assessments of the risk of TSE disease transmission via oral exposure. Indeed, the applicant's recent study describing the effects of host age on TSE susceptibility (Brown et al. 2009 J. Immunol. 183, 5199) was discussed at the November 2009 meeting of the UK Spongiform Encephalopathies Advisory Committee (for minutes see http://www.seac.gov.uk/papers/103-2.pdf) and received significant media interest (eg: BBC website http://news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/8307551.stm).

Depending on the data generated from this study it is plausible that pharmaceutical companies may have significant interest in data generated from this study. Therefore, during the course of the project the applicant will consult with the Institute's Business Development and Commercialisation Department to seek potential Industry partners to exploit the project's data.

This study will enable the scientists working on the project to acquire many transferable skills. Important skills will be gained in two major disciplines: mucosal immunology and TSE diseases. During the course of this study the scientist will develop import skills in in vivo biology (a currently recognised priority for research) and high resolution bioimaging. This is a collaborative project with internationally recognised researchers. As a consequence, the scientists will gain invaluable additional expertise and develop their team-working, networking and collaboration skills.

Data from this study will be disseminated to the UK and international scientific communities in a timely manner through a combination of publication in quality peer-reviewed journals and presentation at scientific meetings including: international and national scientific conferences, seminars at other research institutions and lectures to undergraduate students. Dr. Mabbott is regularly invited to present data at these events. Appropriate opportunities will be taken to communicate the project's findings to the public. Dr. Mabbott was recently involved in Public Engagement activities for Brain Awareness Week (Univ. Edinburgh). This involved teaching primary school pupils some basic biology of the human brain through short practical examples. Dr. Mabbott is keen to explore similar opportunities to communicate data from this project in a similar manner through his activities as a BBSRC-funded Schools Regional Champion. The release of potential news-worthy publications would be discussed with the Institute and BBSRC press officers and press releases issued when appropriate. Dr Mabbott's recent study in the Journal of Immunology (Brown 2009) was handled in such manner and covered by national and international media including The Times newspaper and BBC news website.