Dectin-1 uses novel mechanisms for yeast phagocytosis in macrophages

Abstract

The phagocytosis of pathogens is a critical event in host defense, not only for clearance of the invading microorganism, but also for the subsequent immune response. We have examined Dectin-1, a proinflammatory nonopsonic receptor for ␤-glucans, and show that it mediates the internalization of ␤-glucan-bearing ligands, including yeast particles. Although requiring tyrosine phosphorylation and the cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM)-like motif, uptake mediated by Dectin-1 was different from any previously reported phagocytic receptor and was not dependent on Syk-kinase in macrophages. IntroductionPhagocytosis plays a critical role in innate immunity, both by facilitating the removal and killing of pathogens and by priming the adaptive immune response. The phagocytic process is initiated by the cross-linking of an array of dedicated surface receptors, some capable of direct recognition, the so-called pattern recognition receptors (PRRs), and others that recognize opsonins coating the pathogens. Of these receptors, the opsonic Fc␥ (Fc␥Rs) and complement receptors (CRs) are the best described and exhibit different phagocytic mechanisms and subsequent cellular responses that reflect important differences in their signaling pathways. 1,2 Nonopsonic PRRs, such as the macrophage mannose receptor, scavenger receptors, and recently CEACAM3, [3][4][5] have also been suggested to possess phagocytic capacity, but the mechanisms underlying these activities are less clear.We have identified Dectin-1 as the major macrophage PRR for ␤-glucans, carbohydrate polymers that possess anti-infective and antitumorigenic properties in vivo. [6][7][8] Dectin-1, which is also expressed on the surface of other innate immune cells, including neutrophils and dendritic cells, 9 is a C-type lectinlike transmembrane receptor containing an immunoreceptor tyrosine-based activation motif (ITAM)-like motif in its cytoplasmic tail, which becomes tyrosine phosphorylated on ligand binding. 10,11 We and others have shown this motif was required for proinflammatory cytokine production, in collaboration with the Toll-like receptors (TLRs), and for induction of the respiratory burst in response to ␤-glucan ligands, including fungal pathogens. 11,12 The proinflammatory properties of Dectin-1 are similar to those of the ITAM-containing Fc␥Rs, which also mediate the internalization of immune complexes. 13 Phagocytosis by Fc␥R, after ligand binding, is thought to be initiated by src kinase-mediated tyrosine phosphorylation of the receptor ITAM domains leading to the recruitment of p72Syk, a protein tyrosine kinase that is required for subsequent cellular activation and ligand internalization. 1,14 Although the exact downstream pathways leading from Fc␥ and other receptors to actin polymerization and phagocytosis is currently unclear, other molecules, including phosphatidylinositol (PI)-3 kinase, protein kinase C (PKC), and the Rho guanosine triphosphatases (GTPases), are known to be involved. 1 We determined if Dectin-1 could als...

NADPH oxidase of human dendritic cells: Role in Candida albicans killing and regulation by interferons, dectin‐1 and CD206

“…It is known that DC interact with yeasts essentially by the mannose-binding receptors CD206 [22,31] and DCspecific intercellular adhesion molecule-grabbing nonintegrin (DC-SIGN) [32,33], the b-glucan receptor dectin-1 [27,32,[34][35][36][37], and TLR2 [32,38,39]. Therefore, we analyzed Candida uptake in the presence of mannan, which binds both CD206 and DC-SIGN [40,41] and interferes with particle internalization by these receptors [42], or laminarin, a specific dectin-1 inhibitor [27,35,40,41,43]. Fig.…”

The Shaving Reaction: Rituximab/CD20 Complexes Are Removed from Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia Cells by THP-1 Monocytes

“…This inhibitor interferes with actin filament formation, showing that this process is crucial for the shaving reaction. Interestingly, however, none of the inhibitors that block specific signaling pathways important for phagocytosis (47) was able to inhibit shaving, showing that shaving and phagocytosis are mechanistically distinct. Finally, we found that a protease inhibitor mixture blocked shaving (Fig.…”

“…However, shaving was not blocked by tyrosine kinase inhibitors known to block phagocytosis (Fig. 8A) (47). Phagocytosis is characterized by sequential phosphorylation of cellular proteins mediated by Src and Syk kinases (66), whereas simple endocytosis of small Ab-Ag complexes does not require tyrosine kinase action (23).…”

“…One group targets signaling pathways known to be involved in phagocytosis (47). These inhibitors can therefore provide information as to whether phagocytosis and shaving are governed by similar processes.…”

“…THP-1 cells were exposed to the following signal transduction inhibitors for 60 min at 37°C, before being mixed with donor cells: 5 g/ml cytochalasin D, 15 M PP2, 15 M PP3, 50 M piceattanol, 150 M genistein, or 100 ng/ml wortmannin, or for 15 min at 37°C with 10 M chelerythrine (47). To test for the role of THP-1-associated proteases, THP-1 cells were preincubated for 9 h with a protease inhibitor mixture that contained 2 mM 4-(2-aminoethyl)benzenesulfonyl fluoride, 1 mM EDTA, 5 mM 1,10-phenanthroline, 130 M bestatin, 14 M E-64, 1 M leupeptin, and 0.3 M aprotinin (48).…”