Pathogens as sensors for measuring immune defence efficiency in the on-going infection

• Applicant: Professor Dr. Andreas Müller
• Subject Area: Immunology ; Parasitology and Biology of Tropical Infectious Disease Pathogens
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262050617

Understanding how the immune defence impacts on pathogen biology is of fundamental importance: The immune system's mode of action, i.e. whether a pathogen is killed, inhibited in its growth, or spatially confined, has broad implications for the outcome of the infection, immunopathology, and the pathogen's susceptibility to treatment. However, it has so far been impossible to determine the mode of action of an on-going immune response. In the presented project, we will use in vivo reporter systems in the intracellular parasite Leishmania major to analyse how the pathogen reacts to the stress imposed by the immune system. This will be achieved via fluorescent protein constructs that permit the measurement of two different biological parameters in the living parasite: (1) the activity of stress-related proteases and (2) the integrity of the parasite's cellular membrane. The strategy of using pathogens as sensors for the output of immune effector activity will enable us to map the immune defence according to its actual effect on pathogen physiology. By using intravital 2-photon microscopy, we will be able to survey the mode of action of a protective immune response in the course of an on-going infection. Using inhibitors and knockout mice deficient in the production of reactive oxygen and nitrogen intermediates (ROI and RNI), we will also determine the importance of specific cellular defence mechanisms for the different modes of action of pathogen containment. By applying ROI/RNI production inhibitors in transgenic mice with fluorescently labelled phagocyte populations, we will analyse the requirement of ROI/RNI for defence against pathogens in specific cell types. Finally, we will use a mixed bone marrow chimera approach, combining partially ROI production deficient mice with RNI production inhibition, in order to assess the extent of synergism between ROI and RNI in their antimicrobial activity. The proposed experiments will elucidate how cellular defence mechanisms induced by the immune response impact on pathogen biology and how this impact relates to the efficient control of infection. Understanding this relationship will greatly enhance our knowledge of how the immune system carries protective responses into execution.

• DFG Programme: Research Grants