Beta-glucan, which is absent in animal cells, but is a major component of the fungal cell wall, is an important recognition target [6]. Many find more PRRs, including dectin-1 [7], scavenger receptors [8], and complement receptor 3 [9], are capable of binding β-glucan. The signaling cascade triggered by interactions between particulate glucan and dectin-1 involves the sequential activation of spleen tyrosine kinase (Syk), CARD9,

and of the NF-κB and NFAT transcription factors. This pathway leads to phagocytosis, the “respiratory burst”, and cytokine gene induction. The importance of this pathway in anti-fungal host defenses has been demonstrated in experimental infections [10, 11] and is corroborated by the association between increased susceptibility to fungal infection and mutations in human genes encoding for

CARD9 [12]. The Syk/CARD9 pathway is also targeted by other lectin-type PRRs, such as dectin-2, which recognizes cell-wall mannans [13]. Much attention has been devoted to the ability of fungi to activate Toll-like receptors (TLRs) and to the ability of the latter to cooperate with lectin-type receptors in immune responses [14-16]. TLR engagement triggers signaling cascades involving intracellular Ensartinib adaptors, such as MyD88 and TRIF, which result in the activation of several transcription factors, including NF-κB and interferon regulatory factors (IRFs). An important role of TLR-mediated recognition in anti-fungal host defenses is suggested by the extreme susceptibility to infection of MyD88-deficient

mice [14, 17-19]. However, the in vivo role of single TLRs is uncertain [4, 5]. Moreover, the fungal PAMPs responsible for TLR stimulation remain largely undefined, although O-linked mannans and phospholipomannan from C. albicans have been proposed as TLR4 [20] and TLR2 [21] ligands, respectively. Anti-fungal defenses crucially rely on the balanced production of two key cytokines, IL-12p70 and IL-23, which display profound differences in the type of responses that they can elicit in cells of the innate and adaptive immune system. For example, IL-12p70 and IL-23 induce the production of IFN-γ and IL-17, respectively, in T cells. It has been suggested that the production of IL-12p70 and IL-23 are reciprocally regulated through the activation Amobarbital or co-activation of various TLRs and lectin-type receptors [4, 5]. However, little is known of the role of individual TLRs in such activities, especially in the context of infection with whole fungi, as opposed to stimulation with purified, nonfungal PRR agonists. We show here that TLR7-mediated sensing of fungal RNA leads to the production of a number of important cytokines, such as IL-12p70, IL-23, and tumor necrosis factor-alpha (TNF-α). Moreover, TLR7 was required for the induction of IL-12p70, but not IL-23 or TNF-α, in the context of whole yeast stimulation.