Biol. Pharm. Bull. 29(8) 1580—1586 (2006)

expressed on murine macrophages, dendritic cells, and neutrophils. Murine Dectin-1 (mDectin-1) is involved in the recognition of b-glucan, which is the main component of the fungal cell wall, and induces phagocytosis, the generation of reactive oxygen, and the production of proinflammatory cytokines. Thus, it has become clear that various murine anti-fungal immune responses are mediated by Dectin-1. The human homologue of Dectin-1 (hDectin-1) is structurally similar to mDectin-1, with about 60% identity in amino acid sequence. Both murine and human Dectin-1 possess motifs essential for responding to b-glucan. An immunoreceptor tyrosine-based activation motif (ITAM)-like motif consisting of the amino acid sequence (Tyr-X-X-Leu) in the cytoplasmic tail (Fig. 1A) is phosphorylated on stimulation with b-glucan particles and mediates various antifungal activities of Dectin-1. Also in the cytoplasmic tail, three consecutive acidic amino acid residues (Asp-GluAsp) form a putative internalizing signal sequence for the lysosomal endosome. We previously reported that the amino acid sequence (Trp-Ile-His) in the carbohydrate recognition domain (CRD) of Dectin-1 relates to the recognition of b-glucan. The mRNA of Dectin-1 is alternatively spliced and generates several isoforms. In the mouse, two isoforms (isoform A and B) can be generated (Fig. 1B). Isoform A possesses a cytoplasmic tail, transmembrane region, stalk region, and carbohydrate recognition domain (CRD). Meanwhile, isoform B lacks a stalk region consisting of 46 amino acid residues. In humans, there are at least eight isoforms. However, only isoform A and B, which are structurally similar to each of the murine isoforms, function as bglucan receptors. The other human isoforms do not recognize b-glucan because they lack a b-glucan recognition site in the CRD. One major difference among the four functional isoforms of murine and human Dectin-1 is the number and position of the N-linked glycosylation sites. Both of the mouse isoforms have two N-linked glycosylation sites in their CRD. In contrast, human isoform A has an N-linked glycosylation site in its stalk region, and isoform B has no glycosylation site because it lacks a stalk region. N-Linked glycosylation on cell surface receptors is generally recognized to increase the stability of a molecule, promote cell surface expression, and often modulate ligand-binding activities. The importance of glycosylation on some C-type lectin family receptors has also been reported, but the effect of the glycosylation of Dectin-1 has not been clarified. In this study, we generated various glycosylation-site mutants of murine and human Dectin-1, and demonstrated that Nlinked glycosylation on Dectin-1 is essential for cell surface expression, ligand-binding, and the activation of nuclear factor kB (NF-kB) together with toll-like receptor 2 (TLR2). These results suggest that N-linked glycosylation affects the anti-fungal activities of Dectin-1.