Projects

1. Immunity to Parasitic Worms - Recruitment and Functions of Effector Leukocytes

As parasitic worms pass through host tissues, acute inflammatory and granulomatous infiltrates can be elicited. Eosinophils are often a distinctive feature of these infiltrates and so we have been examining the impact of eosinophilia on host resistance to a number of different parasite species. We have shown that eosinophilic interleukin-5 (IL-5) transgenic mice are very resistant to infections with the nematode Nippostrongylus brasiliensis and we have strong evidence to suggest that it is eosinophils that are responsible for protecting the host against this parasite. We are currently determining where N. brasiliensis larvae are killed as they migrate through host tissues and how eosinophils and other leukocytes interact with the parasite. In IL-5 transgenic mice many larvae are killed within 24 hours of a primary infection, most probably at the site of inoculation. We are collaborating with colleagues in Canberra and the USA to assess the importance of proteins which are either unique to eosinophils or that regulate eosinophil function. Transgenic and gene knock-out mice are being used to assess cytokine, chemokine and eosinophil granule proteins that may be important in protecting the host against the parasite or in reducing tissue damage. We have also established that N. brasiliensis fails to develop or produce eggs in the small intestines of IL-5 transgenic mice. We are therefore defining the nature of the intestinal mucosal immune response to N. brasiliensis, characterizing factors that might adversely affect parasite development and fecundity, as well as those that could regulate tissue repair.

2. How Do Host Leukocytes Recognize Parasitic Worms?

We know that eosinophils are rapidly recruited into the skin after injection of larvae of the parasitic worm, N. brasiliensis. These and other leukocytes quickly attach to parasite larvae and can kill them. With Professors David Gordan (Flinders University Adelaide) and Marina Botto (Imperial College, London), we are assessing the involvement of complement proteins in targeting eosinophils to the surface of the parasite. Mice in which genes encoding complement proteins have been knocked out (eg. C1q, factor B and C3 KO mice) will be used to analyze the importance of complement in controlling parasite infections. We are also determining if N. brasiliensis larvae can evade this innate defence mechanism by making use of proteins that down-regulate complement activity. Eosinophils may also use other innate pattern recognition receptors to bind to parasites and the targets for these receptors may change as the parasite passes through different life cycle stages. The Honours projects that might be generated by this work could include techniques such as protein expression and purification, Western blotting, flow cytometry and in vivo studies of infection. We have also developed a series of in vitro assays that will be used to assess interactions between leukocytes and parasites.

3. Immune Evasion Strategies Used by Parasites to Avoid Destruction in the Host

Although resistant to N. brasiliensis, IL-5 transgenic mice are just as susceptible as wild type animals to some other parasite species. The nematode Toxocara canis induces intense eosinophilia after invading host tissues, but seems impervious to attack by these or other leukocytes. We are currently investigating how this and other parasites evade host defences and in particular, how parasites avoid destruction by eosinophils. This parasite and other parasites secrete lectin-like protein and with the help of our collaborators in Brisbane and Edinburgh, such molecules will be assessed for their capacity to interfere with leukocyte function. Parasites use many strategies to evade host immunity and produce an array of molecules to cripple particular components of immune responses. This is bad for the host, but perhaps it opens up new opportunities in biotechnology. Antibiotics and immunosuppressive drugs derived from fungi and bacteria are already the basis of major pharmaceuticals. Can molecules secreted by parasites also be developed as therapeutic agents, for example as immunosuppressive drugs to be used in organ transplantation and in the treatment of autoimmune or inflammatory diseases? Could we use products derived from parasites to control the immunopathology of allergic inflammatory diseases like asthma, where eosinophils are thought to have a negative impact? Basic science underpins most useful developments in biotechnology and this could be a good starting point for an Honours student with a particular interest in applied science. This project could include recombinant protein expression and purification, Western blotting, flow cytometry, in vitro assays of interactions between leukocytes and parasites and in vivo studies of infection.

4. Eosinophils and Asthma

Asthma is a common disease that affects approximately 10% of people in South Australia. The principal objective of this experimental study is to determine why only some individuals in the population are susceptible to this disease. In recent years we have learnt that the fundamental abnormality in asthma is a specific type of airways inflammation and tissue remodelling in which IL-5 and eosinophils could play a central role. Some strains of mice, when sensitized and challenged with an allergen, develop asthma-like responses, including bronchoconstriction. Although all strains tested in our laboratory develop very significant inflammation, only some show plugging of the airways and loss of lung function. Eosinophils and the cytokines that influence them may be responsible for some of the more adverse features of this baffling disease. We hope to identify factors that might influence the number of eosinophils recruited to the lungs and the actions of these cells when they arrive. While we know from our recent studies in reproductive biology that eosinophils can contribute to normal tissue development and remodelling, in a disease like asthma, eosinophils initially recruited to protect and repair, may ultimately contribute to airways damage. Our collaborators in Canberra have recently established the importance of eosinophils as antigen presenting cells in models of allergic asthma. Eosinophils may accelerate the disease process in asthma by stimulating T cells to produce IL-13, a cytokine known to drive allergic responses. Obviously an important new challenge is to determine what eosinophils do to T cells and to establish if this is more tightly regulated in strains of mice that do not develop the full asthma phenotype. Rapid clearance of eosinophils from the site of inflammation may be one way in which allergic responses are controlled and so we are currently interested in defining rates of leukocyte apoptosis. These and other important observations from our research teams, form the basis of several potential Honours projects. As with all of our projects, when investigating airways inflammation we use a wide range of techniques. For example, we have measured airway hyperreactivity (AHR) in mice to determine if eosinophil infiltration can be associated with functional impairment of the lungs. Future studies might also include measurements of cytokines and chemokine production using ELISA and RTPCR, assays for apoptosis, lymphocyte culture, immunohistochemistry and flow cytometry.