The regulation of protective immunity to viruses by L-selectin

Virus infections in animals and humans cause morbid and fatal diseases which incur a severe economic burden. The ability of animals and humans to combat viruses depends on a subset of white blood cells called T lymphocytes. When a virus enters the body, T lymphocytes are presented with virus extracts in local lymph glands and turned into killer T cells before they are despatched to fight the virus. Some killer T cells turn into memory T cells which remember the virus and prevent re-infection. How killer T cells find their way to virus infected tissues, such as influenza infected lungs, is not understood.

Our latest work has identified a homing molecule on killer T cells, called L-selectin, that directs them to virus-infected tissues and maintains immune memory to that virus. L-selectin is lost from the surface of T lymphocytes as they turn into killer T cells. So more of it needs to be made by the killer T-cells before they leave the lymph glands, otherwise they can't sense detect infected cells in the body. By increasing the expression of L-selectin on killer T cells we can increase the number of killer T cells at the site of infection and boost killing of virus. However, if T lymphocytes do not make more L-selectin they are unable to locate where virus is growing and clear it from the body

In this proposal we want to find out how the level of L-selectin on the surface of killer T cells is controlled and what effect L-selectin has on memory T cells. We will also identify how L-selectin senses a virus-infected tissue by finding what binds to it to make T-lymphocytes go to the virus infected organs. There are currently no anti-viral drugs for many of the viruses that cause significant morbidity in animals and mortality in young and elderly humans. Furthermore, vaccines are either not available or need to be re-formulated every season, like with influenza. Our studies of killer T cell homing have revealed a new way of boosting the immune system. This is by increasing the homing of killer T cells to virus infected tissues. Understanding how L-selectin is involved in killer T cells will help to develop new approaches to combat viral infections in people and livestock.

This proposal is based on our newly established concept that L-selectin on cytotoxic T cells is inextricably linked to the protective function of T cells in controlling virus infections. Using two evolutionarily distinct viruses that infect mucosal and visceral organs (influenza and vaccinia), we have shown that L-selectin expression is essential to deliver cytotoxic T cells to virus-infected organs for protective immunity. Moreover, genetically modified cytotoxic T cells which do not downregulate L-selectin are better at clearing virus due to increased recruitment into virus-infected tissues whereas L-selectin deficient cytotoxic T cells are unable to control virus replication despite being activated normally in lymph nodes. In a new study we have found that memory to influenza virus requires L-selectin expression on CD8+ T cells. How L-selectin expression is regulated on influenza-specific cytotoxic T cells will be key to understanding its role in conferring protective immunity to the virus and this is the first aim of the proposal. The second aim is to determine the impact of L-selectin on the development, localisation and function of memory T cells. Our findings predict that expression of ligands for L-selectin is an important mechanism, whereby influenza-specific T cells detect where influenza virus is replicating in the body and may regulate the development and persistence of memory T cells. The final aim of the proposal will characterize influenza-induced ligands for L-selectin in infected tissues and determine how they are regulated. Our study will provide a mechanistic understanding of how L-selectin controls protective immunity to influenza virus at the molecular level.

Who will benefit?
The proposal will study fundamental aspects of lymphocyte recruitment from the bloodstream to sites of infection and how this is linked to protecting the body from invading pathogens. Our proposal that protective immunity to viruses can be boosted by promoting T lymphocyte homing to virus-infected tissues is novel. This principle is more widely applicable and we are currently exploring whether this approach can be used in cancer immunotherapy. The proposed research will benefit academics as well as biotechnology industries interested in how immunity to infectious agents is regulated by
immune cell trafficking and will provide new knowledge for the development of vaccines and other therapies to combat debilitating virus infections as well as cancer. The research provides vital skills training in in vivo immune cell trafficking and has wider educational benefit to postgraduate and postdoctoral scientists, as well as undergraduate science and medical school students in understanding how the immune system combats infection.
How will they benefit
Identification of strategies to boost protective immunity to viruses will contribute to improving the nation's health by combating the large number of viruses that infect animals and humans. Training of Ph.D. students and post-doctoral scientists in strategic skills of in vivo immunology and leucocyte trafficking will expand the expertise base within the UK and internationally in key areas identified by the research councils of being of high priority. The investigators host Cardiff University undergraduate biomedical science and intercalating medical and dental students for 8-week projects on a regular basis, as well as delivering lectures and seminars on Leucocyte Trafficking, Protein Engineering and Metalloproteinase Biology to science, medical and dental students. In addition, the PIs hosts biomedical students on the European Lifelong Learning ERASMUS programme.
The PIs (individually and through the Cardiff Institute for Tissue Engineering and Repair network) engage regularly with the public/potential stakeholders (local Schools, science centres, Soapbox Science, charity open days, TV, radio, newspapers, the aged community, presentations to MPs, links with clinicians) and direct dissemination to the scientific community (publications, conferences, workshops). The Schools of Medicine and Dentistry organise annual "Science in Health-Live" event whereby all Year 12 pupils in Wales and border counties are invited to attend in order to learn about the biomedical research at our institute. The event includes lectures, exhibitions, question-panels and tours and routinely attracts more than 500 students who are contemplating careers in the health sciences. Recently, Dr Ager delivered a lecture entitled 'Directing the Traffic: how do white blood cells know where to go?' Additional ad hoc work experience visits and Nuffield Foundation Science Bursary projects are arranged through contacts established during the Science in Health event. We are actively interested in communicating our work by participating in public lectures, open days for schools, work experience placements for school and undergraduate students from within the UK and Europe, which widely disseminates ongoing research in Cardiff into the interplay between viruses and the immune system.
Cardiff University also co-ordinates a monthly series of "Science in Health Public Lectures" that are open to the general public as a well as six-form pupils. The aim of these lectures is to open up areas of concern in health care and present new research on health issues to the public. It is envisaged that one of these forthcoming lectures will be given on the topic of Leucocyte trafficking in Infection and Immunity and will highlight ongoing research in Cardiff.