Immunology and Immunopathology of visceral leishmaniasis

Leishmaniasis is a disease caused when people are bitten by sandflies that contain a small single cell parasite, called Leishmania. Although some people never get sick, many develop local skin ulcers or a potentially fatal disease that affects the internal organs, called visceral leishmaniasis (kala azar or ?black sickness?). Why different people get different types of disease is not known, but it may relate to the type of Leishmania they are infected with and their health of their immune system. 2 million people get leishmaniasis every year (in 88 countries, including some in Europe) and visceral leishmaniasis is responsible for over 60,000 deaths annually. As the parasites live deep in the tissues (spleen, liver, bone marrow), it is difficult in sick people to see exactly how they are affecting our immune system and to find ways to improve how the immune system deals with them. Therefore, we need to use experimental models of the disease to study these questions. Although much progress has been made, experimental models cannot provide the whole picture and there may be important differences in how mice and people respond to these parasites, or in how much damage the immune system does to our organs trying to fight the infection. We wish to conduct an integrated research programme to let us study disease processes in human and mouse tissues side by side. This approach is important, both to see whether the responses in mice also occur in man (thus supporting clinical study of drugs/vaccines developed in mice) and conversely to see whether we can improve the predictive nature of models used for testing drugs/vaccines. We will be studying how Leishmania is eaten by white blood cells (phagocytes) in the liver, and how the expression of our genes changes in response to the infection. We will develop new microscopy approaches that allow us to see how infection affects phagocyte function and their ability to coordinate inflammation. We will use tissues samples taken from people during treatment and also at post mortem, to observe how well their immune systems have responded to treatment or to understand what went wrong that led to their death. In combination, these studies will provide much important new information on human disease, and help to reduce and improve the quality of animal experimentation.

Leishmaniasis represents a spectrum of diseases associated with infection by the protozoan parasite, Leishmania. Of global importance, with approximately 2M new cases reported annually from 88 countries, leishmaniasis ranks high amongst parasitic diseases for its impact on public health. Visceral leishmaniasis (VL), caused by L. donovani and L. infantum/chagasi is a leading cause of parasite-associated mortality. Research on VL thus holds potential for major benefits to health. In addition, the study of this intracellular parasite continues to increase our fundamental understanding of the host-parasite interface and immune function. Building on the exciting achievements of our previous MRC supported research, we now seek to develop a fully-integrated programme, using animal models, human liver-slice culture and clinical histopathology, to explore the diverse roles played by mononuclear phagocytes in VL (as host, regulator of inflammation / immunity, and mediator of pathology).



To study the biology of tissue-resident macrophages in their natural environment, we will define (at the molecular and cellular level) the in situ response of murine and human Kupffer cells to L. donovani infection and the downstream consequences for the initiation of inflammation. We will perform comparative mRNA and miRNA profiling of human and mouse Kupffer cells, and validate potential mediators of inflammation using dynamic imaging approaches in human and murine liver. New tools will allow us to examine the function of Kupffer cells in established granulomas in mice. We will perform comparative histopathology of spleen / LN from mice and patients with VL, to determine whether the lymphoid tissue remodelling associated with parasite persistence and immunosuppression in mice is also evident in human disease, and using intra-vital imaging in combination with mice that allow cell-specific and temporal depletion and lineage tracing, we will define the involvement of mononuclear phagocytes in this process. Informed by histopathology and transcriptional profiling, we will develop new models of hepatic infection that reflect more closely the diversity of response seen in man. Likewise, we will exploit recently identified sites of cryptic infection in mice to develop a greater understanding of the mechanisms underlying post kala azar dermal leishmaniasis, mucosal disease and secondary infection.



Collectively, the data generated in this Programme will test a number of new hypotheses related to mononuclear phagocyte function in VL, help to cross-validate existing and new mouse models and, by providing new comparative data on disease pathogenesis, increase the likelihood of effective translation of our research into new prophylactic or therapeutic interventions.