Intravital imaging of the interaction of the pathogenic fungus Aspergillus fumigatus with cells of the innate and adaptive immune system

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A. fumigatus is a saprophytic fungus, which is ubiquitously dispersed in the environment. Since it is constantly producing large amounts of conidia for asexual reproduction, the breathing air contains 1-100 m-3 conidia and every individual is constantly inhaling several 100 conidia per day. This rarely causes health problems for immunocompetent persons, as also huge amounts of conidia are easily cleared by cells of the innate immune system. However, the appearance of large cohorts of immunecompromised patients due to clinical intervention, e.g. in transplantation medicine or oncology or due to AIDS has made A. fumigatus a major cause of death among these patients in the last two decades. Today, the most fatal form of infection, invasive Aspergillosis (IA), is considered as the number one cause for infectious death in hematological patients. Research of the last 10-15 years on the role of the immune system in IA has shown that phagocytes, especially alveolar macrophages (AM) and neutrophils play a major role in A. fumigatus defense. But also the adaptive immune system has been shown to be important for the outcome of IA. The major problem with the previous work is that so far investigation of A. fumigatus defense has only been possible "post mortem", i.e. the cells, which have successfully fought an infection or the animals, which have succumbed to it, were not analyzed directly during the process of infection. Therefore, current concepts as to the in vivo events of IA are mainly correlative. Especially in the case of adaptive immunity A. fumigatus research has been hampered by the lack of an appropriate model system. In this proposal we intend to close these gaps. In a first project we will analyze the interaction and response of the innate immune system with A. fumigatus. Thereby, we will directly observe living cells during their interaction with the fungus under circumstances, where the animal successfully fights or succumbs to an infection. As a completely new approach we will do this by intravital microscopy in living animals. The second project deals with the development of a new A. fumigatus strain, which carries a model antigen, that can be recognized by T cells from T cell receptor transgenic mouse lines. This approach allows us to monitor the de novo development of an adaptive immune response in vivo by classical methods such as histology and flow cytometry and also by intravital imaging in the living animal. Thus, these two projects should lead to a completely understanding of the in vivo events leading to the development or fight of IA.