Chitin, Chitinase Responses, and Invasive Fungal Infections
Figure 2
Fungal cell wall pathogen-associated molecular patterns (PAMPs) and their host-pattern recognition receptors (PRRs). Various fungal cell wall components are recognized by specific PRRs. Some PAMPs are recognized by multiple PRRs; for example, N-linked mannan is recognized by mannan receptor (MR), dectin-2, and FcR [46, 47]. Phospholipomannan-(PLM-) coated -glucans are recognized by both TLR-6 and TLR-2 [53, 54]. Other receptors may involve the signaling pathway of another PRR. For example, galectin-3, which recognizes -mannosides, signals through TLR-2 (represented by a curved arrow) [47, 49] dectin-1, when activated by -glucans can signal to activate the nuclear factor kappa-lightchain enhancer of activated B cells (NF-B) on its own or with the help of TLR-2 [4, 45]. Fc gamma receptor (FcR) may signal through dectin-2 when activated by N-linked mannan [3, 45, 47, 55]. Recognition of these fungal cell wall components mediates fungal recognition and defense by the host. Recognition by host PRRs usually involves signaling through NF-B and activation of proinflammatory cytokines, such as TNF-, or in some instances, and anti-inflammatory cytokines such as interleukin (IL)-10 [45]. The possibility of an alternative chitin receptor exists, activation of which leads to the recruitment of IL-4 producing cells [45, 59]. However, chitin has been shown to function as a T helper (Th)1 immune modulator, which stands in contrast an IL-4 associated Th2 response [60–64].
