Interaction between the opportunistic pathogen Aspergillus fumigatus and its host

Abstract

Fungal infections are worldwide, with 1.5 million deaths each year, an increasing problem, especially due to the increased use of immunosuppressive medication. One of the main problems are the infections caused by Aspergillus fumigatus. This fungus is found worldwide, and the spores are easily dispersed via the air. On a daily basis humans inhale hundreds of these conidia. A group with a high risk for such infections are patients with a defective or weakened immune system. After inhalation these conidia end up in the lung, where they can develop to an invasive infection with high mortality rates. In healthy individuals this fungus can cause non-invasive infections. In this thesis the defense mechanisms of conidia against the human immune system are studied. The conidia of Aspergillus fumigatus are covered with a green pigment layer. It was thought that this pigment layer is the main defense against hydrogen peroxide, which is used by the immune system to kill the fungus. This study shows that this dogma is not true for Aspergillus fumigatus. Instead, it was shown that the absence of a catalase is responsible for the increased sensitivity for hydrogen peroxide in contrast to previous studies. This study shows that the absence of this secreted catalase can play a more important role during invasive aspergillosis as previously thought. This could also mean that this enzyme might be a new potential target for antifungals.