Tuberculosis remains a fatal disease caused by Mycobacterium tuberculosis, which contains various unique components that affect the host immune system. Trehalose-6,6′-dimycolate (TDM; also called cord factor) is a mycobacterial cell wall glycolipid that is the most studied immunostimulatory component of M. tuberculosis. Despite five decades of research on TDM, its host receptor has not been clearly identified. Here, we demonstrate that macrophage inducible C-type lectin (Mincle) is an essential receptor for TDM. Heat-killed mycobacteria activated Mincle-expressing cells, but the activity was lost upon delipidation of the bacteria; analysis of the lipid extracts identified TDM as a Mincle ligand. TDM activated macrophages to produce inflammatory cytokines and nitric oxide, which are completely suppressed in Mincle-deficient macrophages. In vivo TDM administration induced a robust elevation of inflammatory cytokines in sera and characteristic lung inflammation, such as granuloma formation. However, no TDM-induced lung granuloma was formed in Mincle-deficient mice. Whole mycobacteria were able to activate macrophages even in MyD88-deficient background, but the activation was significantly diminished in Mincle/MyD88 double-deficient macrophages. These results demonstrate that Mincle is an essential receptor for the mycobacterial glycolipid, TDM.

Macrophage-inducible C-type lectin (Mincle) is expressed mainly in macrophages and is induced after exposure to various stimuli and stresses. Here we show that Mincle selectively associated with the Fc receptor common gamma-chain and activated macrophages to produce inflammatory cytokines and chemokines. Mincle-expressing cells were activated in the presence of dead cells, and we identified SAP130, a component of small nuclear ribonucloprotein, as a Mincle ligand that is released from dead cells. To investigate whether Mincle is required for normal responses to cell death in vivo, we induced thymocyte death by irradiating mice and found that transient infiltration of neutrophils into the thymus could be blocked by injection of Mincle-specific antibody. Our results suggest that Mincle is a receptor that senses nonhomeostatic cell death and thereby induces the production of inflammatory cytokines to drive the infiltration of neutrophils into damaged tissue.

Mincle (also called as Clec4e and Clecsf9) is a C-type lectin receptor expressed in activated phagocytes. Recently, we have demonstrated that Mincle is an FcR␥-associated activating receptor that senses damaged cells. To search an exogenous ligand(s), we screened pathogenic fungi using cell line expressing Mincle, FcR␥, and NFAT-GFP reporter. We found that Mincle specifically recognizes the Malassezia species among 50 different fungal species tested. Malassezia is a pathogenic fungus that causes skin diseases, such as tinea versicolor and atopic dermatitis, and fatal sepsis. However, the specific receptor on host cells has not been identified. Mutation of the putative mannose-binding motif within C-type lectin domain of Mincle abrogated Malassezia recognition. Analyses of glycoconjugate microarray revealed that Mincle selectively binds to ␣-mannose but not mannan. Thus, Mincle may recognize specific geometry of ␣-mannosyl residues on Malassezia species and use this to distinguish them from other fungi. Malassezia activated macrophages to produce inflammatory cytokines/ chemokines. To elucidate the physiological function of Mincle, Mincle-deficient mice were established. Malassezia-induced cytokine/chemokine production by macrophages from Mincle ؊/؊ mice was significantly impaired. In vivo inflammatory responses against Malassezia was also impaired in Mincle ؊/؊ mice. These results indicate that Mincle is the first specific receptor for Malassezia species to be reported and plays a crucial role in immune responses to this fungus.ITAM ͉ macrophages ͉ signal transduction

Cord factor, also called trehalose-6,6'-dimycolate (TDM), is a potent mycobacterial adjuvant. We herein report that the C-type lectin MCL (also called Clec4d) is a TDM receptor that is likely to arise from gene duplication of Mincle (also called Clec4e). Mincle is known to be an inducible receptor recognizing TDM, whereas MCL was constitutively expressed in myeloid cells. To examine the contribution of MCL in response to TDM adjuvant, we generated MCL-deficient mice. TDM promoted innate immune responses, such as granuloma formation, which was severely impaired in MCL-deficient mice. TDM-induced acquired immune responses, such as experimental autoimmune encephalomyelitis (EAE), was almost completely dependent on MCL, but not Mincle. Furthermore, by generating Clec4e(gfp) reporter mice, we found that MCL was also crucial for driving Mincle induction upon TDM stimulation. These results suggest that MCL is an FcRγ-coupled activating receptor that mediates the adjuvanticity of TDM.

Various C-type lectin receptors (CLRs), including Mincle and Dectin-2, function as pattern recognition receptors and play a central role in immunity to fungal pathogens. However, the precise structures of the CLR ligands in various pathogenic fungi have yet to be completely defined. Here we report that Malassezia, an opportunistic skin fungal pathogen, is cooperatively recognized by Mincle and Dectin-2 through distinct ligands. Solvent-based fractionation revealed that Mincle and Dectin-2 recognize lipophilic and hydrophilic components of Malassezia, respectively. Mass spectrometry and nuclear magnetic resonance (NMR) revealed glyceroglycolipid and unique mannosyl fatty acids linked to mannitol as two Mincle ligands. An O-linked mannobiose-rich glycoprotein was identified as a Malassezia ligand for Dectin-2. Cytokine production in response to the Mincle ligands and the Dectin-2 ligand was abrogated in Mincle(-/-) and Dectin-2(-/-) dendritic cells, respectively. These results demonstrate that Mincle and Dectin-2 recognize distinct ligands in Malassezia to induce host immune responses.