Project: Strategies of Candida albicans and Candida glabrata to exit from macrophages

  Candida cells (green) in interaction with macrophages Copyright: © Brunke/Hube Candida cells (green) in interaction with macrophages: While Candida glabrata continues to grow inside of modified phagosomes until the macrophages burst (left), Candida albicans rapidly forms hyphal filaments to escape the immune cells (right).

Candida albicans and C. glabrata are the two most common human pathogenic yeasts, responsible for superficial and life-threatening systemic infections with high morbidity and mortality. Although phylogenetically very different and following distinct infection strategies, both species have developed similar immune evasion mechanisms. For example, both fungi can survive and proliferate in macrophages and share the ability to inhibit phagosomal maturation and acidification. Importantly, both can also exit phagocytes, but differ in their escape patterns: C. albicans rapidly escapes phagosomes and causes macrophage cell death within hours, while C. glabrata only escapes after a longer persistence period. Furthermore, C. glabrata does not cause any obvious immune activation, while C. albicans triggers inflammatory responses such as inflammasome activation and NLRP3-mediated pyroptosis.

Several studies suggest that C. albicans filamentation plays an important role for exit from macrophages by causing phagosomal rupture, inducing host cell damage and killing, and facilitating escape. However, it remains unclear or controversial how hypha formation is triggered and precisely how host cells are damaged and killed. In particular, the mode of action of the hypha-associated toxin candidalysin inside macrophages and its contribution to host cell escape is ambiguous. In contrast to C. albicans, C. glabrata does not form hyphae and grows in the yeast morphology within macrophages. Yet, these proliferating yeasts kill their host cells and later escape by unknown mechanisms. Finally, the mechanisms by which both species acquire nutrients for intracellular growth and the host factors which may inhibit, prevent or foster fungal proliferation and escape are largely unknown.

In this project, we will (a) investigate the triggers for C. albicans hypha formation inside macrophages, (b) study how C. albicans and C. glabrata acquire nutrients inside macrophages, (c) identify and characterize fungal factors associated with phagosomal damage, host cell killing and exit, and (d) explore how host cells can be treated to limit or block intracellular fungal proliferation and escape.

We will do this by using methods established in our laboratory, including in vitro infection models based on primary macrophages and cell lines, microscopic imaging, transcriptional and single cell profiling as well as molecular biology approaches to generate Candida mutants and to screen available large-scale mutant libraries. Phenotypic screenings and cell biology approaches will be done in collaboration with national and international partners. In collaboration with partners of SPP 2225 we will analyse programmed cell death pathways, the involvement of fungal phospholipases, and the localization and function of candidalysin during escape. Results will be compared to other models within SPP 2225 to identify conserved and fungal-specific mechanism which allow the escape from macrophages.