Mammalian Pattern Recognition Receptors (PRRs) Involved in Recognition of Fungi

There are over 100,000 fungal species currently identified, some of which live as commensals in the microbiome of mammalian skin and mucosal surfaces. However, several opportunistic fungi can cause life-threatening invasive infections that lead to over 1.5 million deaths across the globe each year. The four main species that cause invasive infections are Candida, Aspergillus, Cryptococcus, and Pneumocystis. The immune response to these pathogens is initiated through pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs), including components of the fungal cell wall, RNA, and DNA. Following recognition, PRRs initiate phagocytosis, neutrophil extracellular trap (NET) formation, the respiratory burst, inflammasome activation, and production of chemokines and cytokines that drive inflammatory responses and shape the adaptive immune system. This chapter will focus on the PRRs that recognize PAMPs from the four main human fungal pathogens, Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, and Pneumocystis jirovecii. More specifically, we discuss PRRs from the C-type lectin receptor (CLR) family, the Toll-like receptor (TLRTLR) family, and some other receptors that have known fungal ligands and briefly discuss the role of these receptors during antifungal immunity.