Publications (94) View all
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Article: Inhibition of antibody production in vivo by pre-stimulation of Toll-like receptor 4 before antigen priming is caused by defective B cell priming and not impairment in antigen presentation.
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ABSTRACT: Stimulation of Toll-like receptor 4 (TLR4) induces not only innate but also adaptive immune responses, and has been suggested to exert adjuvant effects. Additional to such positive effects, pre-stimulation of TLR4 induces endotoxin tolerance where animals are unresponsive to subsequent lethal challenges with lipopolysaccharide (LPS). We examined the effects of pre-stimulation of TLR4 using agonistic anti-TLR4 mAbs (UT12) on antibody production in vivo. Pre-injection of UT12 prior to both primary and secondary immunization completely inhibited antigen-specific antibody responses. Cellular analysis revealed that the inhibition was not due to impairment of T cell activation. Accordingly, T helper activities in UT12 pre-injected mice were not impaired. In contrast, B cell priming was defective in UT12 pre-injected mice. The observation that the expression of activation markers such as CD69 and CD86 on B cells was blocked by UT12 pre-injection supports this. Interestingly, UT12 pre-injection only showed inhibitory effects at the primary and not the secondary immunization. These results provide important information concerning the regulatory mechanisms of antibody production, especially in endotoxin-tolerant states.International Immunology 10/2012; · 3.41 Impact Factor -
Article: Tetrameric interaction of the ectoenzyme CD38 on the cell surface enables its catalytic and raft-association activities.
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ABSTRACT: The leukocyte cell-surface antigen CD38 is the major nicotinamide adenide dinucleotide glycohydrolase in mammals, and its ectoenzyme activity is involved in calcium mobilization. CD38 is also a raft-dependent signaling molecule. CD38 forms a tetramer on the cell surface, but the structural basis and the functional significance of tetramerization have remained unexplored. We identified the interfaces contributing to the homophilic interaction of mouse CD38 by site-specific crosslinking on the cell surface with an expanded genetic code, based on a crystallographic analysis. A combination of the three interfaces enables CD38 to tetramerize: one interface involving the juxtamembrane α-helix is responsible for the formation of the core dimer, which is further dimerized via the other two interfaces. This dimerization of dimers is required for the catalytic activity and the localization of CD38 in membrane rafts. The glycosylation prevents further self-association of the tetramer. Accordingly, the tetrameric interaction underlies the multifaceted actions of CD38.Structure 08/2012; 20(9):1585-95. · 6.35 Impact Factor -
Article: Structural basis of interleukin-5 dimer recognition by its α receptor.
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ABSTRACT: Interleukin-5 (IL-5), a major hematopoietin, stimulates eosinophil proliferation, migration, and activation, which have been implicated in the pathogenesis of allergic inflammatory diseases, such as asthma. The specific IL-5 receptor (IL-5R) consists of the IL-5 receptor α subunit (IL-5RA) and the common receptor β subunit (βc). IL-5 binding to IL-5R on target cells induces rapid tyrosine phosphorylation and activation of various cellular proteins, including JAK1/JAK2 and STAT1/STAT5. Here, we report the crystal structure of dimeric IL-5 in complex with the IL-5RA extracellular domains. The structure revealed that IL-5RA sandwiches the IL-5 homodimer by three tandem domains, arranged in a "wrench-like" architecture. This association mode was confirmed for human cells expressing IL-5 and the full-length IL-5RA by applying expanded genetic code technology: protein photo-cross-linking experiments revealed that the two proteins interact with each other in vivo in the same manner as that in the crystal structure. Furthermore, a comparison with the previously reported, partial GM-CSF•GM-CSFRA•βc structure enabled us to propose complete structural models for the IL-5 and GM-CSF receptor complexes, and to identify the residues conferring the cytokine-specificities of IL-5RA and GM-CSFRA.Protein Science 03/2012; 21(6):850-64. · 2.80 Impact Factor -
Article: Glycyrrhizin and isoliquiritigenin suppress the LPS sensor toll-like receptor 4/MD-2 complex signaling in a different manner.
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ABSTRACT: Recent evidences suggest that the extracts of plant products are able to modulate innate immune responses. A saponin GL and a chalcone ILG are representative components of Glycyrrhiza uralensis, which attenuate inflammatory responses mediated by TLRs. Here, we show that GL and ILG suppress different steps of the LPS sensor TLR4/MD-2 complex signaling at the receptor level. Extract of G. uralensis suppressed IL-6 and TNF-α production induced by lipid A moiety of LPS in RAW264.7 cells. Among various G. uralensis-related components of saponins and flavanones/chalcones, GL and ILG could suppress IL-6 production induced by lipid A in dose-dependent manners in RAW264.7 cells. Furthermore, elevation of plasma TNF-α in LPS-injected mice was attenuated by passive administration of GL or ILG. GL and ILG inhibited lipid A-induced NF-κB activation in Ba/F3 cells expressing TLR4/MD-2 and CD14 and BMMs. These components also inhibited activation of MAPKs, including JNK, p38, and ERK in BMMs. In addition, GL and ILG inhibited NF-κB activation and IL-6 production induced by paclitaxel, a nonbacterial TLR4 ligand. Interestingly, GL attenuated the formation of the LPS-TLR4/MD-2 complexes, resulting in inhibition of homodimerization of TLR4. Although ILG did not affect LPS binding to TLR4/MD-2, it could inhibit LPS-induced TLR4 homodimerization. These results imply that GL and ILG modulate the TLR4/MD-2 complex at the receptor level, leading to suppress LPS-induced activation of signaling cascades and cytokine production, but their effects are exerted at different steps of TLR4/MD-2 signaling.Journal of leukocyte biology 03/2012; 91(6):967-76. · 4.99 Impact Factor -
Article: The radioprotective 105/MD-1 complex contributes to diet-induced obesity and adipose tissue inflammation.
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ABSTRACT: Recent accumulating evidence suggests that innate immunity is associated with obesity-induced chronic inflammation and metabolic disorders. Here, we show that a Toll-like receptor (TLR) protein, radioprotective 105 (RP105)/myeloid differentiation protein (MD)-1 complex, contributes to high-fat diet (HFD)-induced obesity, adipose tissue inflammation, and insulin resistance. An HFD dramatically increased RP105 mRNA and protein expression in stromal vascular fraction of epididymal white adipose tissue (eWAT) in wild-type (WT) mice. RP105 mRNA expression also was significantly increased in the visceral adipose tissue of obese human subjects relative to nonobese subjects. The RP105/MD-1 complex was expressed by most adipose tissue macrophages (ATMs). An HFD increased RP105/MD-1 expression on the M1 subset of ATMs that accumulate in eWAT. Macrophages also acquired this characteristic in coculture with 3T3-L1 adipocytes. RP105 knockout (KO) and MD-1 KO mice had less HFD-induced adipose tissue inflammation, hepatic steatosis, and insulin resistance compared with wild-type (WT) and TLR4 KO mice. Finally, the saturated fatty acids, palmitic and stearic acids, are endogenous ligands for TLR4, but they did not activate RP105/MD-1. Thus, the RP105/MD-1 complex is a major mediator of adipose tissue inflammation independent of TLR4 signaling and may represent a novel therapeutic target for obesity-associated metabolic disorders.Diabetes 03/2012; 61(5):1199-209. · 8.29 Impact Factor
