Chitinases in Invasive Fungal Infections

Immunocompromised people (due to e.g. illness or chemotherapy) are at risk for a pulmonary fungal infection: invasive aspergillosis. Treatment of this infection is challenging. Caspofungin is an agent with antifungal action in high concentrations in vitro, but when given to patients in lower concentrations, it was proven to work. The cause of this discrepancy is unknown.

This thesis investigates the role of the immune system in the antifungal action of caspofungin in the host with invasive pulmonary aspergillosis caused by Aspergillus fumigatus. We focused on the production of chitinases (fungal cell-wall degrading enzymes), which is increased in fungal infections. Signaling proteins such as cytokines are drastically increased in aspergillosis. Treatment with caspofungin causes a subtle change in immune response in terms of chitinase and cytokine production.

Genetic variation in the chitinase genes, resulting in inactive enzymes, did not influence the risk to develop invasive aspergillosis. However, it did influence the risk for mycetoma, a tropical fungal infection that is mainly found in Sudan.

We also tested a novel diagnostic strategy to identify the morphologically identical Aspergillus fumigatus and Aspergillus lentulus. MALDITOF-MS was shown to correctly identify both species. Finally, three novel proteins were tested for antifungal properties, which all showed good antifungal activity against yeasts but not against fungi.

Based on this thesis, we developed the hypothesis that caspofungin changes the fungal cell wall composition, resulting in enhancement of chitinase effects and in synergy with caspofungin. This results in altered cytokines and chemokines, finally leading to better outcomes in patients. Further research might explore therapeutic strategies with synthetic chitinases.