A clonogenic progenitor with prominent plasmacytoid dendritic cell developmental potential.

Macrophage and dendritic cell (DC) progenitors (MDPs) and common DC progenitors (CDPs) are bone marrow (BM) progenitors with DC differentiation potential. However, both MDPs and CDPs give rise to large numbers of conventional DCs (cDCs) and few plasmacytoid DCs (pDCs), implying that more dedicated pDC progenitors remain to be identified. Here we have described DC progenitors with a prominent pDC differentiation potential. Although both MDPs and CDPs express the macrophage colony stimulating factor (M-CSF) receptor (M-CSFR), the progenitors were confined to a M-CSFR(-) fraction, identified as Lin(-)c-Kit(int/lo)Flt3(+)M-CSFR(-), and expressed high amounts of E2-2 (also known as Tcf4) an essential transcription factor for pDC development. Importantly, they appeared to be directly derived from either CDPs or lymphoid-primed multipotent progenitors (LMPPs). Collectively, our findings provide insight into DC differentiation pathways and may lead to progenitor-based therapeutic applications for infection and autoimmune disease.

HTLV-1 bZIP Factor Enhances T-Cell Proliferation by Impeding the Suppressive Signaling of Co-inhibitory Receptors.

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia-lymphoma (ATL) and inflammatory diseases. To enhance cell-to-cell transmission of HTLV-1, the virus increases the number of infected cells in vivo. HTLV-1 bZIP factor (HBZ) is constitutively expressed in HTLV-1 infected cells and ATL cells and promotes T-cell proliferation. However, the detailed mechanism by which it does so remains unknown. Here, we show that HBZ enhances the proliferation of expressing T cells after stimulation via the T-cell receptor. HBZ promotes this proliferation by influencing the expression and function of multiple co-inhibitory receptors. HBZ suppresses the expression of BTLA and LAIR-1 in HBZ expressing T cells and ATL cells. Expression of T cell immunoglobulin and ITIM domain (TIGIT) and Programmed cell death 1 (PD-1) was enhanced, but their suppressive effect on T-cell proliferation was functionally impaired. HBZ inhibits the co-localization of SHP-2 and PD-1 in T cells, thereby leading to impaired inhibition of T-cell proliferation and suppressed dephosphorylation of ZAP-70 and CD3ζ. HBZ does this by interacting with THEMIS, which associates with Grb2 and SHP-2. Thus, HBZ interacts with the SHP containing complex, impedes the suppressive signal from PD-1 and TIGIT, and enhances the proliferation of T cells. Although HBZ was present in both the nucleus and the cytoplasm of T cells, HBZ was localized largely in the nucleus by suppressed expression of THEMIS by shRNA. This indicates that THEMIS is responsible for cytoplasmic localization of HBZ in T cells. Since THEMIS is expressed only in T-lineage cells, HBZ mediated inhibition of the suppressive effects of co-inhibitory receptors accounts for how HTLV-1 induces proliferation only of T cells in vivo. This study reveals that HBZ targets co-inhibitory receptors to cause the proliferation of infected cells.

Correction: HTLV-1 bZIP Factor Enhances T-cell Proliferation by Impeding the Suppressive Signaling of Co-inhibitory Receptors.

[This corrects the article DOI: 10.1371/journal.ppat.1006120.].

The Ly49Q receptor plays a crucial role in neutrophil polarization and migration by regulating raft trafficking.

Neutrophils rapidly undergo polarization and directional movement to infiltrate the sites of infection and inflammation. Here, we show that an inhibitory MHC I receptor, Ly49Q, was crucial for the swift polarization of and tissue infiltration by neutrophils. During the steady state, Ly49Q inhibited neutrophil adhesion by preventing focal-complex formation, likely by inhibiting Src and PI3 kinases. However, in the presence of inflammatory stimuli, Ly49Q mediated rapid neutrophil polarization and tissue infiltration in an ITIM-domain-dependent manner. These opposite functions appeared to be mediated by distinct use of effector phosphatase SHP-1 and SHP-2. Ly49Q-dependent polarization and migration were affected by Ly49Q regulation of membrane raft functions. We propose that Ly49Q is pivotal in switching neutrophils to their polarized morphology and rapid migration upon inflammation, through its spatiotemporal regulation of membrane rafts and raft-associated signaling molecules.

Absence of DCIR1 reduces the mortality rate of endotoxemic hepatitis in mice.

Dendritic cell immunoreceptor (DCIR) is a C-type lectin with an immunoreceptor tyrosine-based inhibitory motif (ITIM). Mice lacking DCIR1 (Dcir1-/- mice) show higher susceptibility to chronic arthritis with increasing age, suggesting that DCIR1 is involved in immune modulation via its ITIM. However, the role of DCIR1 in acute immune responses is not clear. In this study, we explored its role in acute experimental hepatitis. Upon injection of d-galactosamine and lipopolysaccharide, Dcir1-/- mice showed decreased mortality rates and serum levels of alanine aminotransferase. In early onset hepatitis, serum levels of TNF-α, which primarily cause inflammation and hepatocyte apoptosis, were significantly lower in Dcir1-/- mice than in WT mice. In the liver of Dcir1-/- mice, influx of neutrophils and other leukocytes decreased. Consistently, the levels of neutrophil-chemoattractant chemokine CXCL1/KC, but not CXCL2/MIP-2, were lower in Dcir1-/- mice than in WT mice. However, chemotaxis of Dcir1-/- neutrophils to CXCL1/KC appeared normal. Pervanadate treatment induced binding of DCIR1 and Src homology region 2 domain-containing phosphatase (SHP)-2, possibly leading to CXCL1/KC expression. These results suggest that DCIR1 is involved in exacerbation of endotoxemic hepatitis, providing a new therapeutic target for lethal hepatitis.

Functional evaluation of activation-dependent alterations in the sialoglycan composition of T cells.

Sialic acids (Sias) are often conjugated to the termini of cellular glycans and are key mediators of cellular recognition. Sias are nine-carbon acidic sugars, and, in vertebrates, the major species are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), differing in structure at the C5 position. Previously, we described a positive feedback loop involving regulation of Neu5Gc expression in mouse B cells. In this context, Neu5Gc negatively regulated B-cell proliferation, and Neu5Gc expression was suppressed upon activation. Similarly, resting mouse T cells expressed principally Neu5Gc, and Neu5Ac was induced upon activation. In the present work, we used various probes to examine sialoglycan expression by activated T cells in terms of the Sia species expressed and the linkages of Sias to glycans. Upon T-cell activation, sialoglycan expression shifted from Neu5Gc to Neu5Ac, and the linkage shifted from α2,6 to α2,3. These changes altered the expression levels of sialic acid-binding immunoglobulin-like lectin (siglec) ligands. Expression of sialoadhesin and Siglec-F ligands increased, and that of CD22 ligands decreased. Neu5Gc exerted a negative effect on T-cell activation, both in terms of the proliferative response and in the context of activation marker expression. Suppression of Neu5Gc expression in mouse T and B cells prevented the development of nonspecific CD22-mediated T cell-B cell interactions. Our results suggest that an activation-dependent shift from Neu5Gc to Neu5Ac and replacement of α2,6 by α2,3 linkages may regulate immune cell interactions at several levels.

Dendritic cell immunoreceptor 1 alters neutrophil responses in the development of experimental colitis.

BACKGROUND: Ulcerative colitis, an inflammatory bowel disease, is associated with the massive infiltration of neutrophils. Although the initial infiltration of neutrophils is beneficial for killing bacteria, it is presumed that persistent infiltration causes tissue damage by releasing antibacterial products as well as inflammatory cytokines. A murine C-type lectin receptor, dendritic cell immunoreceptor 1 (Dcir1), is expressed on CD11b(+) myeloid cells, such as macrophages, dendritic cells and neutrophils. It was reported that Dcir1 is required to maintain homeostasis of the immune system to prevent autoimmunity, but it is also involved in the development of infectious disease resulting in the enhanced severity of cerebral malaria. However, the role of Dcir1 in intestinal immune responses during colitis remains unclear. In this study, we investigated the role of Dcir1 in intestinal inflammation using an experimental colitis model induced with dextran sodium sulfate (DSS). RESULTS: In contrast to wild type (WT) mice, Dcir1 (-/-) mice exhibited mild body weight loss during the course of DSS colitis accompanied by reduced colonic inflammation. Dcir1 deficiency caused a reduced accumulation of neutrophils in the inflamed colon on day 5 of DSS colitis compared with WT mice. Consistently, the production of a neutrophil-attracting chemokine, MIP-2, was also decreased in the Dcir1 (-/-) colon compared with the WT colon on day 5. There were fewer myeloperoxidase-positive neutrophils in the inflamed colon of Dcir1 (-/-) mice than in that of WT mice. Moreover, bone marrow neutrophils from Dcir1 (-/-) mice produced less reactive oxygen species (ROS) by lipopolysaccharide stimulation than those from WT mice. This suggests that Dcir1 deficiency decreases the accumulation of tissue destructive neutrophils during DSS colitis. CONCLUSION: Dcir1 enhances the pathogenesis of DSS colitis by altering neutrophil recruitment and their functions.

Amyloid ß oligomers induce interleukin-1ß production in primary microglia in a cathepsin B- and reactive oxygen species-dependent manner.

Amyloid ß (Aß) peptide, a causative agent of Alzheimer's disease, forms two types of aggregates: oligomers and fibrils. These aggregates induce inflammatory responses, such as interleukin-1ß (IL-1ß) production by microglia, which are macrophage-like cells located in the brain. In this study, we examined the effect of the two forms of Aß aggregates on IL-1ß production in mouse primary microglia. We prepared Aß oligomer and fibril from Aß (1-42) peptide in vitro. We analyzed the characteristics of these oligomers and fibrils by electrophoresis and atomic force microscopy. Interestingly, Aß oligomers but not Aß monomers or fibrils induced robust IL-1ß production in the presence of lipopolysaccharide. Moreover, Aß oligomers induced endo/phagolysosome rupture, which released cathepsin B into the cytoplasm. Aß oligomer-induced IL-1ß production was inhibited not only by the cathepsin B inhibitor CA-074-Me but also by the reactive oxygen species (ROS) inhibitor N-acetylcysteine. Random chemical crosslinking abolished the ability of the oligomers to induce IL-1ß. Thus, multimerization and fibrillization causes Aß oligomers to lose the ability to induce IL-1ß. These results indicate that Aß oligomers, but not fibrils, induce IL-1ß production in primary microglia in a cathepsin B- and ROS-dependent manner.

Human CD1c⁺ myeloid dendritic cells acquire a high level of retinoic acid-producing capacity in response to vitamin D3.

All-trans-retinoic acid (RA) plays a critical role in maintaining immune homeostasis. Mouse intestinal CD103⁺ dendritic cells (DCs) produce a high level of RA by highly expressing retinal dehydrogenase (RALDH)2, an enzyme that converts retinal to RA, and induce gut-homing T cells. However, it has not been identified which subset of human DCs produce a high level of RA. In this study, we show that CD1c⁺ blood myeloid DCs (mDCs) but not CD141(high) mDCs or plasmacytoid DCs exhibited a high level of RALDH2 mRNA and aldehyde dehydrogenase (ALDH) activity in an RA- and p38-dependent manner when stimulated with 1α,25-dihydroxyvitamin D3 (VD3) in the presence of GM-CSF. The ALDH activity was abrogated by TLR ligands or TNF. CD103⁻ rather than CD103⁺ human mesenteric lymph node mDCs gained ALDH activity in response to VD3. Furthermore, unlike in humans, mouse conventional DCs in the spleen and mesenteric lymph nodes gained ALDH activity in response to GM-CSF alone. RALDH2(high) CD1c⁺ mDCs stimulated naive CD4⁺ T cells to express gut-homing molecules and to produce Th2 cytokines in an RA-dependent manner. This study suggests that CD1c⁺ mDCs are a major human DC subset that produces RA in response to VD3 in the steady state. The "vitamin D-CD1c⁺mDC-RA" axis may constitute an important immune component for maintaining tissue homeostasis in humans.

Identification of a novel type 2 innate immunocyte with the ability to enhance IgE production.

Fas (CD95), a member of the tumor necrosis factor receptor superfamily, mediates apoptosis-inducing signals in its expressing cells, especially in self-reactive cells. We recently reported that Fas(-/-) mice with a BALB/c background (BALB/c Fas(-/-) mice) developed blepharitis with allergic inflammation that was accompanied by hyper-IgE production. Here, we found a novel type of immunocyte in the spleen of BALB/c Fas(-/-) mice, which enhanced the production of IgE by B cells in the presence of IL-4 and CD40 signaling in vitro. The immunocyte did not express lineage markers but expressed Thy-1 and Sca-1 just like recently identified type 2 innate lymphoid cells, such as natural helper (NH) cells and nuocytes. However, they did not express c-Kit, IL-7R and IL-33R (T1/ST2), important markers of type 2 innate lymphoid cells. Instead, our identified Lin(-)Thy-1(+)Sca-1(+) cells expressed IL-18R and secreted Th2 cytokines when co-cultured with B cells or when stimulated with IL-18 and IL-2. Moreover, we found essentially the same type of cells in BALB/c wild-type mice as in BALB/c Fas(-/-) mice, which enhanced IgE production in contact with B cells in vitro. These cells from BALB/c wild-type mice expressed Fas and were sensitive to Fas-mediated apoptosis. Collectively, the newly identified Lin(-)Thy-1(+)Sca-1(+) cell, which we designated a F-NH cell (Fas-expressing natural helper cell), is a novel type 2 innate immunocyte with activity to enhance IgE production from B cells with the help of IL-4 and CD40 signaling. F-NH cells may play an important role in the development of chronic allergic inflammation.

Efficient capture of Candida albicans and zymosan by SIGNR1 augments TLR2-dependent TNF-α production.

SIGNR1, a mouse C-type lectin, binds various pathogens, including Candida albicans. In this study, we explore the impact of SIGNR1 in the recognition of C. albicans/zymosan and the subsequent tumor necrosis factor (TNF)-α production using SIGNR1-transfected RAW264.7 (RAW-SIGNR1) cells and resident peritoneal macrophages. Compared with RAW-control cells, RAW-SIGNR1 cells dramatically enhanced TNF-α production upon the stimulation with heat-killed C. albicans and zymosan. Recognition of microbes via carbohydrate recognition domain (CRD) of SIGNR1 was crucial for the enhanced TNF-α production. Consistently, such an enhancement was significantly decreased by anti-SIGNR1 mAb. Laminarin, antagonistic Dectin-1 ligand, cooperated to further diminish the response, although no effect was observed by itself in RAW-SIGNR1 cells. However, it moderately reduced the response of RAW-control cells. Zymosan depleted of toll-like receptor (TLR) ligands decreased the response, even though it was recognized by SIGNR1 and Dectin-1. Moreover, antagonistic anti-TLR2 abolished the response, suggesting that TNF-α production largely relies on TLR2-mediated signaling. Resident peritoneal macrophages expressing SIGNR1 predominantly captured zymosan injected intra-peritoneally and produced TNF-α, which was dependent on TLR2 and partly inhibited by anti-SIGNR1 mAb. Finally, physical association of SIGNR1 with the extracellular portion of TLR2 through CRD was confirmed by immunoprecipitation using various deletion mutants. These results suggest that SIGNR1 recognizing microbes participates in the enhanced TNF-α production by Mϕ in cooperation with TLR2.

Sulfatide inhibits α-galactosylceramide presentation by dendritic cells.

Sulfatide-reactive type II NKT cells, the so-called non-invariant NKT (non-iNKT) cells, have been shown to counteract invariant NKT (iNKT) cell activity. However, the effects of sulfatide on activation of iNKT cells by α-galactocylceramide (αGC) in the context of CD1d have not been studied in detail. Therefore, we studied the blocking effect of sulfatide on αGC-induced iNKT cell activation by dendritic cells (DCs). Even in the absence of non-iNKT cells, sulfatide inhibited αGC-mediated iNKT cell activation by reducing αGC/CD1d complex formations in a dose-dependent manner. This was also confirmed in a cell-free setting using immobilized CD1d-Ig. Moreover, simultaneous injection of αGC with sulfatide decreased αGC/CD1d complex formations on DCs, accompanied by the reduced CD40L-up-regulation and IFN-γ production by iNKT cells and IL-12p70 production by DCs. However, sulfatide by itself did not interfere with the presentation of MHC class II-mediated antigen presentation to specific T cells. These results demonstrate that sulfatide competes with αGC to be loaded onto CD1d along the endocytic pathway in DCs, thereby inhibiting the iNKT cell response.

IRF-2 regulates B-cell proliferation and antibody production through distinct mechanisms.

Interferon regulatory factor (IRF)-2 is a transcription factor involved in type I (IFN- α/ß) signaling. It has been reported that IRF-2 deficiency results in various immune dysfunctions. However, the role of IRF-2 in B-cell functions needs to be elucidated. Unlike wild-type (WT) B cells, IRF-2(-/-) B2 cells were refractory to anti-IgM, but not LPS. Such a defect in proliferation was dependent on IFN- α/ß receptor (IFNAR). Marginal zone B cells increased in the proportion relative to B2 cells in IRF-2(-/-) mice produced IgM normally to LPS stimulation. However, IRF-2(-/-) B2 cells were defective in IgM production in an IFNAR-independent manner, although both B-cell subsets differentiated phenotypically to plasma cells at elevated efficiencies. Class switch recombination of IRF-2(-/-) B2 cells by LPS plus IL-4 was also impaired. Their reduced IgM production was conceivably due to an inefficient up-regulation of Blimp-1. Consistent with these in vitro observations, specific antibody production in vivo to a T-dependent antigen by B2 cells was severely impaired in IRF-2(-/- )mice. However, a low, but significant, level of IgG was detected at a late time point, and this IgG exhibited comparable binding affinity to that in WT mice. Follicular helper T-cell development and germinal center formation were normal. A similar tendency was observed when µ chain(-/-) mice were reconstituted with IRF-2(-/- )B cells. These results revealed a multi-faceted role of IRF-2 in the function of B cells, particularly B2 cells, through regulating proliferation in an IFNAR-dependent manner and antibody production via up-regulation of Blimp-1.

Langerhans cells are critical in epicutaneous sensitization with protein antigen via thymic stromal lymphopoietin receptor signaling.

BACKGROUND: The clarification of cutaneous dendritic cell subset and the role of thymic stromal lymphopoietin (TSLP) signaling in epicutaneous sensitization with protein antigens, as in the development of atopic dermatitis, is a crucial issue. OBJECTIVES: Because TSLP is highly expressed in the vicinity of Langerhans cells (LCs), we sought to clarify our hypothesis that LCs play an essential role in epicutaneous sensitization with protein antigens through TSLP signaling. METHODS: By using Langerin-diphtheria toxin receptor knock-in mice and human Langerin-diphtheria toxin A transgenic mice, we prepared mice deficient in LCs. We also prepared mice deficient in TSLP receptors in LCs by using TSLP receptor-deficient mice with bone marrow chimeric technique. We applied these mice to an ovalbumin (OVA)-induced epicutaneous sensitization model. RESULTS: Upon the epicutaneous application of OVA, conditional LC depletion attenuated the development of clinical manifestations as well as serum OVA-specific IgE increase, OVA-specific T-cell proliferation, and IL-4 mRNA expression in the draining lymph nodes. Consistently, even in the steady state, permanent LC depletion resulted in decreased serum IgE levels, suggesting that LCs mediate the T(H)2 local environment. In addition, mice deficient in TSLP receptors on LCs abrogated the induction of OVA-specific IgE levels upon epicutaneous OVA sensitization. CONCLUSION: LCs initiate epicutaneous sensitization with protein antigens and induce T(H)2-type immune responses via TSLP signaling.

Difference in fine specificity to polysaccharides of Candida albicans mannoprotein between mouse SIGNR1 and human DC-SIGN.

C-type lectin SIGNR1 directly recognizes Candida albicans and zymosan and has been considered to share properties of polysaccharide recognition with human DC-SIGN (hDC-SIGN). However, the precise specificity of SIGNR1 and the difference from that of hDC-SIGN remain to be elucidated. We prepared soluble forms of SIGNR1 and hDC-SIGN and conducted experiments to examine their respective specificities. Soluble SIGNR1 (sSIGNR1) bound several types of live C. albicans clinical isolate strains in an EDTA-sensitive manner. Inhibition analyses of sSIGNR1 binding by glycans from various yeast strains demonstrated that SIGNR1 preferentially recognizes N-glycan α-mannose side chains in Candida mannoproteins, as reported in hDC-SIGN. Unlike shDC-SIGN, however, sSIGNR1 recognized not only Saccharomyces cerevisiae, but also C. albicans J-1012 glycan, even after α-mannosidase treatment that leaves only ß1,2-mannose-capped α-mannose side chains. In addition, glycomicroarray analyses showed that sSIGNR1 binds mannans from C. albicans and S. cerevisiae but does not recognize Lewis(a/b/x/y) antigen polysaccharides as in shDC-SIGN. Consistent with these results, RAW264.7 cells expressing hDC-SIGN in which the carbohydrate recognition domain (CRD) was replaced with that of SIGNR1 (RAW-chimera) produced comparable amounts of interleukin 10 (IL-10) in response to glycans from C. albicans and S. cerevisiae, but those expressing hDC-SIGN produced less IL-10 in response to S. cerevisiae than C. albicans. Furthermore, RAW-hDC-SIGN cells remarkably reduced IL-10 production after α-mannosidase treatment compared with RAW-chimera cells. These results indicate that SIGNR1 recognizes C. albicans/yeast through a specificity partly distinct from that of its homologue hDC-SIGN.

C-type lectin SIGNR1 enhances cellular oxidative burst response against C. albicans in cooperation with Dectin-1.

We investigated the role of SIGNR1 in the recognition of Candida albicans and the subsequent cellular oxidative burst response. Soluble SIGNR1 (sSIGNR1) tetramer bound equally to zymosan and both heat-killed (HK) and live C. albicans in an EDTA-sensitive manner, whereas sDectin-1 tetramer predominantly bound to zymosan and HK-microbes in an EDTA-independent manner. In cellular response, enhanced oxidative burst was observed in RAW264.7 cells expressing SIGNR1 (RAW-SIGNR1) compared with RAW-control cells upon stimulation with HK-C. albicans and zymosan. This response was independent of TLR2 and the cytosolic portion of SIGNR1 but dependent on the recognition by SIGNR1 via carbohydrate recognition domain. Antagonistic laminarin and anti-Dectin-1 mAb cooperatively reduced the response with mannan and anti-SIGNR1 mAb, respectively, although they had no effect by themselves. Moreover, oxidative response and bactericidal activity largely relied on Syk-mediated signaling. RAW-SIGNR1 cells not only captured microbes more efficiently but also showed higher responses than RAW-control cells. Similar enhanced responses were observed in SIGNR-1-expressing resident peritoneal Mϕ. Interestingly, Dectin-1 was recruited to the phagosomal membrane upon the stimulation and physically associated with SIGNR1. These results suggest that SIGNR1 plays a significant role in inducing oxidative response to C. albicans by Syk-dependent signaling, possibly through Dectin-1.

Rho-mDia1 pathway is required for adhesion, migration, and T-cell stimulation in dendritic cells.

Dendritic cells (DCs) are essential for the initiation of acquired immune responses through antigen acquisition, migration, maturation, and T-cell stimulation. One of the critical mechanisms in this response is the process actin nucleation and polymerization, which is mediated by several groups of proteins, including mammalian Diaphanous-related formins (mDia). However, the role of mDia in DCs remains unknown. Herein, we examined the role of mDia1 (one of the isoforms of mDia) in DCs. Although the proliferation and maturation of bone marrow-derived DCs were comparable between control C57BL/6 and mDia1-deficient (mDia1(-/-)) mice, adhesion and spreading to cellular matrix were impaired in mDia1(-/-) bone marrow-derived DCs. In addition, fluorescein isothiocyanate-induced cutaneous DC migration to draining lymph nodes in vivo and invasive migration and directional migration to CCL21 in vitro were suppressed in mDia1(-/-) DCs. Moreover, sustained T-cell interaction and T-cell stimulation in lymph nodes were impaired by mDia1 deficiency. Consistent with this, the DC-dependent delayed hypersensitivity response was attenuated by mDia1-deficient DCs. These results suggest that actin polymerization, which is mediated by mDia1, is essential for several aspects of DC-initiated acquired immune responses.

Spatiotemporal regulation of intracellular trafficking of Toll-like receptor 9 by an inhibitory receptor, Ly49Q.

Toll-like receptor (TLR) 9 recognizes unmethylated microorganismal cytosine guanine dinucleotide (CpG) DNA and elicits innate immune responses. However, the regulatory mechanisms of the TLR signaling remain elusive. We recently reported that Ly49Q, an immunoreceptor tyrosine-based inhibitory motif-bearing inhibitory receptor belonging to the natural killer receptor family, is crucial for TLR9-mediated type I interferon production by plasmacytoid dendritic cells. Ly49Q is expressed in plasmacytoid dendritic cells, macrophages, and neutrophils, but not natural killer cells. In this study, we showed that Ly49Q regulates TLR9 signaling by affecting endosome/lysosome behavior. Ly49Q colocalized with CpG in endosome/lysosome compartments. Cells lacking Ly49Q showed a disturbed redistribution of TLR9 and CpG. In particular, CpG-induced tubular endolysosomal extension was impaired in the absence of Ly49Q. Consistent with these findings, cells lacking Ly49Q showed impaired cytokine production in response to CpG-oligodeoxynucleotide. Our data highlight a novel mechanism by which TLR9 signaling is controlled through the spatiotemporal regulation of membrane trafficking by the immunoreceptor tyrosine-based inhibitory motif-bearing receptor Ly49Q.

Invariant NKT cell anergy is induced by a strong TCR-mediated signal plus co-stimulation.

Vα14 TCR expressing invariant NK T (iNKT) cells recognize α-galactosylceramide (αGC)/CD1d complex and produce large amounts of various cytokines before the onset of the adaptive immunity. After stimulation with a high dose (2-5 µg) of αGC in vivo, iNKT cells in the spleen and liver become anergic in terms of the proliferation and cytokine production to subsequent stimulation. In this study, we monitor how iNKT anergy is induced. Anergized iNKT cells dramatically reduced the expression of IL-2Rα, and exogenous IL-2 restored the ability to proliferate and produce IL-4 but not to produce IFN-γ. Anergized iNKT cells expressed high levels of programmed death-1 (PD-1). However, iNKT cells in PD-1-deficient mice became anergic as a result of αGC injection, as do normal mice. Furthermore, anti-PD-1 blocking mAb was unable to restore their responsiveness. When iNKT cells were stimulated with immobilized anti-CD3 in the presence or absence of anti-CD28, they produced cytokines in a dose-dependent manner. Unlike in naive CD4 T cells, the strong TCR-mediated signaling with co-stimulation renders them anergic to any subsequent stimulation with αGC and spleen dendritic cells (DCs). Moreover, iNKT cells also became anergic after stimulation with phorbol-12-myristate-13-acetate + ionophore. Finally, the injection of αGC-pulsed DCs was more potent in inducing anergy than B cells. These results indicate that strong TCR-mediated activation with co-stimulation provides signals that induce the anergic state in iNKT cells.