Yutaro Kumagai

The Jmjd3- Irf4 axis regulates M2 macrophage polarization and host responses against helminth infection

Polarization of macrophages to M1 or M2 cells is important for mounting responses against bacterial and helminth infections, respectively. Jumonji domain containing-3 (Jmjd3), a histone 3 Lys27 (H3K27) demethylase, has been implicated in the activation of macrophages. Here we show that Jmjd3 is essential for M2 macrophage polarization in response to helminth infection and chitin, though Jmjd3 is dispensable for M1 responses. Furthermore, Jmjd3 (also known as Kdm6b) is essential for proper bone marrow macrophage differentiation, and this function depends on demethylase activity of Jmjd3. Jmjd3 deficiency affected trimethylation of H3K27 in only a limited number of genes. Among them, we identified Irf4 as encoding a key transcription factor that controls M2 macrophage polarization. Collectively, these results show that Jmjd3-mediated H3K27 demethylation is crucial for regulating M2 macrophage development leading to anti-helminth host responses.

LGP2 is a positive regulator of RIG-I– and MDA5-mediated antiviral responses

RNA virus infection is recognized by retinoic acid-inducible gene (RIG)-I–like receptors (RLRs), RIG-I, and melanoma differentiation–associated gene 5 (MDA5) in the cytoplasm. RLRs are comprised of N-terminal caspase-recruitment domains (CARDs) and a DExD/H-box helicase domain. The third member of the RLR family, LGP2, lacks any CARDs and was originally identified as a negative regulator of RLR signaling. In the present study, we generated mice lacking LGP2 and found that LGP2 was required for RIG-I– and MDA5-mediated antiviral responses. In particular, LGP2 was essential for type I IFN production in response to picornaviridae infection. Overexpression of the CARDs from RIG-I and MDA5 in Lgp2−/− fibroblasts activated the IFN-β promoter, suggesting that LGP2 acts upstream of RIG-I and MDA5. We further examined the role of the LGP2 helicase domain by generating mice harboring a point mutation of Lys-30 to Ala (Lgp2K30A/K30A) that abrogated the LGP2 ATPase activity. Lgp2K30A/K30A dendritic cells showed impaired IFN-β productions in response to various RNA viruses to extents similar to those of Lgp2−/− cells. Lgp2−/− and Lgp2K30A/K30A mice were highly susceptible to encephalomyocarditis virus infection. Nevertheless, LGP2 and its ATPase activity were dispensable for the responses to synthetic RNA ligands for MDA5 and RIG-I. Taken together, the present data suggest that LGP2 facilitates viral RNA recognition by RIG-I and MDA5 through its ATPase domain.

Detection of pathogenic intestinal bacteria by Toll-like receptor 5 on intestinal CD11c+ lamina propria cells

Toll-like receptors (TLRs) recognize distinct microbial components and induce innate immune responses. TLR5 is triggered by bacterial flagellin. Here we generated Tlr5−/− 1mice and assessed TLR5 function in vivo. Unlike other TLRs, TLR5 was not expressed on conventional dendritic cells or macrophages. In contrast, TLR5 was expressed mainly on intestinal CD11c+ lamina propria cells (LPCs). CD11c+ LPCs detected pathogenic bacteria and secreted proinflammatory cytokines in a TLR5-dependent way. However, CD11c+ LPCs do not express TLR4 and did not secrete proinflammatory cytokines after exposure to a commensal bacterium. Notably, transport of pathogenic Salmonella typhimurium from the intestinal tract to mesenteric lymph nodes was impaired in Tlr5−/− mice. These data suggest that CD11c+ LPCs, via TLR5, detect and are used by pathogenic bacteria in the intestinal lumen.

Zc3h12a is an RNase essential for controlling immune responses by regulating mRNA decay

Toll-like receptors (TLRs) recognize microbial components, and evoke inflammation and immune responses. TLR stimulation activates complex gene expression networks that regulate the magnitude and duration of the immune reaction. Here we identify the TLR-inducible gene Zc3h12a as an immune response modifier that has an essential role in preventing immune disorders. Zc3h12a-deficient mice suffered from severe anaemia, and most died within 12 weeks. Zc3h12a-/- mice also showed augmented serum immunoglobulin levels and autoantibody production, together with a greatly increased number of plasma cells, as well as infiltration of plasma cells to the lung. Most Zc3h12a-/- splenic T cells showed effector/memory characteristics and produced interferon-γ in response to T-cell receptor stimulation. Macrophages from Zc3h12a-/- mice showed highly increased production of interleukin (IL)-6 and IL-12p40 (also known as IL12b), but not TNF, in response to TLR ligands. Although the activation of TLR signalling pathways was normal, Il6 messenger RNA decay was severely impaired in Zc3h12a-/- macrophages. Overexpression of Zc3h12a accelerated Il6 mRNA degradation via its 3′-untranslated region (UTR), and destabilized RNAs with 3′-UTRs for genes including Il6, Il12p40 and the calcitonin receptor gene Calcr. Zc3h12a contains a putative amino-terminal nuclease domain, and the expressed protein had RNase activity, consistent with a role in the decay of Il6 mRNA. Together, these results indicate that Zc3h12a is an essential RNase that prevents immune disorders by directly controlling the stability of a set of inflammatory genes.

Pathogen recognition by innate receptors.

Microbial infection elicits host immune responses through germline-encoded pattern recognition receptors (PRRs). Toll-like receptors (TLRs) are evolutionarily conserved membrane-bound PRRs that recognize a broad spectrum of microbial components. Recent studies have clarified that two classes of cytosolic receptors, retinoic acid-inducible gene I (RIG-I)-like helicases (RLHs) and nucleotide binding oligomerization domain (NOD)-like receptors (NLRs), play important roles in the cytosolic recognition of invading pathogens. After microbial infection, the host utilizes these receptors differentially to mount robust immune responses. This review will describe pathogen recognition by these receptors, signaling pathways, and their in vivo roles in innate antiviral immunity.

TLR9 as a key receptor for the recognition of DNA

Unmethylated DNA with CpG-motifs is recognized by Toll-like receptor 9 (TLR9) and pleiotropic immune responses are elicited. Macrophages and conventional dendritic cells (cDCs) produce proinflammatory cytokines to B/K-type CpG-DNA, whereas plasmacytoid DCs induce type I interferons to A/D-type CpG-DNA and DNA viruses. The TLR9 mediated signaling pathway is not only responsible for activation of innate immune cells, but also for mounting acquired responses. Thus, it has been attempted to exploit TLR9 ligands as a vaccine adjuvant for anti-cancer immunotherapy. Further, TLR9 mediated signaling is implicated in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus. Nevertheless, recent studies revealed that double-stranded DNA can be recognized by intracellular receptor(s) in a TLR9-independent manner. This review will focus on the roles of TLR9 in immune responses, and its signaling pathways.

TLR7-dependent and FcγR-independent production of type I interferon in experimental mouse lupus

Increased type I interferon (IFN-I) production and IFN-stimulated gene (ISG) expression are linked to the pathogenesis of systemic lupus erythematosus (SLE). Although the mechanisms responsible for dysregulated IFN-I production in SLE remain unclear, autoantibody-mediated uptake of endogenous nucleic acids is thought to play a role. 2,6,10,14-tetramethylpentadecane (TMPD; also known as pristane) induces a lupus-like disease in mice characterized by immune complex nephritis with autoantibodies to DNA and ribonucleoproteins. We recently reported that TMPD also causes increased ISG expression and that the development of the lupus is completely dependent on IFN-I signaling (Nacionales, D.C., K.M. Kelly-Scumpia, P.Y. Lee, J.S. Weinstein, R. Lyons, E. Sobel, M. Satoh, and W.H. Reeves. 2007. Arthritis Rheum. 56:3770–3783). We show that TMPD elicits IFN-I production, monocyte recruitment, and autoantibody production exclusively through a Toll-like receptor (TLR) 7– and myeloid differentiation factor 88 (MyD88)–dependent pathway. In vitro studies revealed that TMPD augments the effect of TLR7 ligands but does not directly activate TLR7 itself. The effects of TMPD were amplified by the Y-linked autoimmune acceleration cluster, which carries a duplication of the TLR7 gene. In contrast, deficiency of Fcγ receptors (FcγRs) did not affect the production of IFN-I. Collectively, the data demonstrate that TMPD-stimulated IFN-I production requires TLR7/MyD88 signaling and is independent of autoantibody-mediated uptake of ribonucleoproteins by FcγRs.

Involvement of the NLRP3 Inflammasome in Innate and Humoral Adaptive Immune Responses to Fungal β-Glucan

Fungal β-glucan, such as curdlan, triggers antifungal innate immune responses as well as shaping adaptive immune responses. In this study, we identified a key pathway that couples curdlan to immune responses. Curdlan promoted the production of the proinflammatory cytokine IL-1β by dendritic cells and macrophages through the NLRP3 inflammasome. Stimulation with Candida albicans and Saccharomyces cerevisiae also triggered the NLRP3 inflammasome-mediated IL-1β production. In vivo, NLRP3 was required for efficient Ag-specific Ab production when curdlan was used as an adjuvant, whereas it was dispensable for the induction of Th1 and Th17 cell differentiation. Furthermore, stimulation of purified B cells with curdlan-induced CD69 up-regulation and IgM production while stimulation with other NLRP3 inflammasome activators, such as silica and aluminum salt, did not. Notably, this induction required NLRP3 but was independent of Toll-like receptor and IL-1 receptor family signaling, suggesting the presence of NLRP3-dependent and IL-1 receptor family independent mechanisms in B cells responsible for Ab responses. Collectively, these findings reveal a critical role for the NLRP3 inflammasome in the regulation of antifungal innate immune responses as well as B cell activation.

Identification and functions of pattern-recognition receptors

Since the identification of Toll-like receptors, our knowledge about pattern-recognition receptors (PRRs) has increased rapidly. Classes of PRRs that have been recently discovered include RIG-I-like receptors, Nod-like receptors, and C-type lectin receptors. Recent studies have started to clarify the molecular basis of PRR-ligand interactions, yet the numbers of PRRs and their ligands continue to increase. New technologies have elucidated the network regulation of immune responses at the cellular and in vivo levels. We review the most recent discoveries about PRRs and their ligands, their roles in intracellular and in vivo regulation of immune responses, and the systems biology of innate immunity.

Lymphocytoid Choriomeningitis Virus Activates Plasmacytoid Dendritic Cells and Induces a Cytotoxic T-Cell Response via MyD88

ABSTRACT Toll-like receptors (TLRs) and retinoic acid-inducible gene I-like helicases (RLHs) are two major machineries recognizing RNA virus infection of innate immune cells. Intracellular signaling for TLRs and RLHs is mediated by their cytoplasmic adaptors, i.e., MyD88 or TRIF and IPS-1, respectively. In the present study, we investigated the contributions of TLRs and RLHs to the cytotoxic T-lymphocyte (CTL) response by using lymphocytoid choriomeningitis virus (LCMV) as a model virus. The generation of virus-specific cytotoxic T lymphocytes was critically dependent on MyD88 but not on IPS-1. Type I interferons (IFNs) are known to be important for the development of the CTL response to LCMV infection. Serum levels of type I IFNs and proinflammatory cytokines were mainly dependent on the presence of MyD88, although IPS-1−/− mice showed a decrease in IFN-α levels but not in IFN-β and proinflammatory cytokine levels. Analysis of Ifna6+/GFP reporter mice revealed that plasmacytoid dendritic cells (DCs) are the major source of IFN-α in LCMV infection. MyD88−/− mice were highly susceptible to LCMV infection in vivo. These results suggest that recognition of LCMV by plasmacytoid DCs via TLRs is responsible for the production of type I IFNs in vivo. Furthermore, the activation of a MyD88-dependent innate mechanism induces a CTL response, which eventually leads to virus elimination.