TCR Signals Controlling Adaptive Immunity against Toxoplasma and Cancer.

T cells play a crucial role in adaptive immunity by recognizing and eliminating foreign pathogens and abnormal cells such as cancer cells. T cell receptor (TCR), which is expressed on the surface of T cells, recognizes and binds to specific antigens presented by major histocompatibility complex (MHC) molecules on antigen-presenting cells (APCs). This activation process leads to the proliferation and differentiation of T cells, allowing them to carry out their specific immune response functions. This chapter outlines the TCR signaling pathways that are common to different T cell subsets, as well as the recently elucidated TCR signaling pathway specific to CD8+ T cells and its role in controlling anti-Toxoplasma and anti-tumor immunity.

Rapid multiplex real-time PCR assay using a portable device for the detection of oral pathogens.

Colonization by several oral pathogens and the onset of oral diseases, such as dental caries and periodontal diseases, are closely related. Therefore, the analysis of pathogens in oral specimens would be helpful for the risk assessment of oral diseases. We developed a rapid multiplex real-time polymerase chain reaction (PCR) method using a portable device and newly designed probe/primer sets to detect the oral pathogens Streptococcus mutans, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia. The theoretical minimum detectable cell numbers of S. mutans, P. gingivalis, T. denticola, and T. forsythia were 1, 1, 4, and 3, respectively. The multiplex real-time PCR system simultaneously detected the colonization of S. mutans and P. gingivalis in human saliva. These results suggest that the multiplex real-time PCR system may be useful for the risk assessment of oral diseases.

A genetic method specifically delineates Th1-type Treg cells and their roles in tumor immunity.

Regulatory T (Treg) cells expressing the transcription factor (TF) Foxp3 also express other TFs shared by T helper (Th) subsets under certain conditions. Here, to determine the roles of T-bet-expressing Treg cells, we generate a mouse strain, called VeDTR, in which T-bet/Foxp3 double-positive cells are engineered to be specifically labeled and depleted by a combination of Cre- and Flp-recombinase-dependent gene expression control. Characterization of T-bet+Foxp3+ cells using VeDTR mice reveals high resistance under oxidative stress, which is involved in accumulation of T-bet+Foxp3+ cells in tumor tissues. Moreover, short-term depletion of T-bet+Foxp3+ cells leads to anti-tumor immunity but not autoimmunity, whereas that of whole Treg cells does both. Although ablation of T-bet+Foxp3+ cells during Toxoplasma infection slightly enhances Th1 immune responses, it does not affect the course of the infection. Collectively, the intersectional genetic method reveals the specific roles of T-bet+Foxp3+ cells in suppressing tumor immunity.

TICAM-1/TRIF associates with Act1 and suppresses IL-17 receptor-mediated inflammatory responses.

TICAM-1 (also called TRIF) is the sole adaptor of TLR3 that recognizes double-stranded RNA. Here, we report that TICAM-1 is involved not only in TLR3 signaling but also in the cytokine receptor IL-17RA signaling. We found that TICAM-1 bound to IL-17R adaptor Act1 to inhibit the interaction between IL-17RA and Act1. Interestingly, TICAM-1 knockout promoted IL-17RA/Act1 interaction and increased IL-17A-mediated activation of NF-κB and MAP kinases, leading to enhanced expression of inflammatory cytokines and chemokines upon IL-17A stimulation. Moreover, Ticam-1 knockout augmented IL-17A-mediated CXCL1 and CXCL2 expression in vivo, resulting in accumulation of myeloid cells. Furthermore, Ticam-1 knockout enhanced delayed type hypersensitivity and exacerbated experimental autoimmune encephalomyelitis. Ticam-1 knockout promoted accumulation of myeloid and lymphoid cells in the spinal cord of EAE-induced mice. Collectively, these data indicate that TICAM-1 inhibits the interaction between IL-17RA and Act1 and functions as a negative regulator in IL-17A-mediated inflammatory responses.

Uncovering a novel role of PLCß4 in selectively mediating TCR signaling in CD8+ but not CD4+ T cells.

Because of their common signaling molecules, the main T cell receptor (TCR) signaling cascades in CD4+ and CD8+ T cells are considered qualitatively identical. Herein, we show that TCR signaling in CD8+ T cells is qualitatively different from that in CD4+ T cells, since CD8α ignites another cardinal signaling cascade involving phospholipase C ß4 (PLCß4). TCR-mediated responses were severely impaired in PLCß4-deficient CD8+ T cells, whereas those in CD4+ T cells were intact. PLCß4-deficient CD8+ T cells showed perturbed activation of peripheral TCR signaling pathways downstream of IP3 generation. Binding of PLCß4 to the cytoplasmic tail of CD8α was important for CD8+ T cell activation. Furthermore, GNAQ interacted with PLCß4, mediated double phosphorylation on threonine 886 and serine 890 positions of PLCß4, and activated CD8+ T cells in a PLCß4-dependent fashion. PLCß4-deficient mice exhibited defective antiparasitic host defense and antitumor immune responses. Altogether, PLCß4 differentiates TCR signaling in CD4+ and CD8+ T cells and selectively promotes CD8+ T cell-dependent adaptive immunity.

miR-451a levels rather than human papillomavirus vaccine administration is associated with the severity of murine experimental autoimmune encephalomyelitis.

Human papilloma virus (HPV) vaccine is currently the most effective prophylaxis to prevent cervical cancer. However, concerns regarding its potential severe adverse reactions have limited the vaccination rate. HPV vaccines have been determined to contain adjuvants which induce inflammation by the innate immune system and are crucial for triggering adaptive immunity. MicroRNA-451a (miR-451a) is located within circulating extracellular vesicles (EVs) and regulates the innate immune response. In this study, we examined the effect of HPV vaccines and EV miR-451a on murine experimental autoimmune encephalomyelitis (EAE), which is an autoimmune disorder that affects the central nervous system. Although HPV vaccine induced pro-inflammatory cytokine expression and macrophage cell death, it failed to exacerbate mouse EAE, whereas circulating EV miR-451a levels were associated with the severity of EAE. Since miR-451a knockout exhibited only marginal effect on the murine EAE clinical score, our data suggest that miR-451a levels reflect an unknown condition associated with EAE severity. Interestingly, excessive uptake of glucose increased EV miR-451a levels both in vitro and in vivo and also exacerbated mouse EAE. Therefore, environmental factors that increase EV miR-451a levels exacerbate the autoimmune disorder more than the HPV vaccine. These observations provide evidence for the safety of HPV vaccines.

Inhibitory effect of black cumin (Nigella sativa) seed essential oil on Fusobacterium nucleatum L-methionine-γ-lyase (L-methioninase) activity.

The enzyme L-methionine-γ-lyase is commonly found in a wide range of bacteria and catalyzes the α-elimination and γ-elimination of L-methionine to produce methyl mercaptan, α-ketobutyrate and ammonia. Black cumin seed essential oil (BC oil) reportedly exhibits deodorizing activity against methyl mercaptan. Therefore, we hypothesized that BC oil may also suppress methyl mercaptan production. In this study, we aimed to evaluate the inhibitory effect of BC oil on L-methionine-γ-lyase activity in Fusobacterium nucleatum. Recombinant L-methionine-γ-lyase was incubated under appropriate conditions with BC oil and its constituent thymoquinone. To analyze L-methionine-γ-lyase activity, α-ketobutyric acid and ammonia concentrations were determined. The concentrations of α-ketobutyric acid and ammonia were significantly decreased by 10 µg mL-1 of BC oil (P < 0.01) and 16.4 µg/mL of thymoquinone (P < 0.05). An enzyme kinetic assay showed a mixed inhibition pattern between L-methionine-γ-lyase and thymoquinone. In conclusion, BC oil not only had a deodorizing effect against methyl mercaptan but also an inhibitory effect on methyl mercaptan production through the suppression of L-methionine-γ-lyase activity. Thymoquinone may be mainly responsible for these effects of BC oil. Thus, application of natural BC oil may be adapted not only for medical use but also in other areas of life.

Initial phospholipid-dependent Irgb6 targeting to Toxoplasma gondii vacuoles mediates host defense.

Toxoplasma gondii is an obligate intracellular protozoan parasite capable of infecting warm-blooded animals by ingestion. The organism enters host cells and resides in the cytoplasm in a membrane-bound parasitophorous vacuole (PV). Inducing an interferon response enables IFN-γ-inducible immunity-related GTPase (IRG protein) to accumulate on the PV and to restrict parasite growth. However, little is known about the mechanisms by which IRG proteins recognize and destroy T. gondii PV. We characterized the role of IRG protein Irgb6 in the cell-autonomous response against T. gondii, which involves vacuole ubiquitination and breakdown. We show that Irgb6 is capable of binding a specific phospholipid on the PV membrane. Furthermore, the absence of Irgb6 causes reduced targeting of other effector IRG proteins to the PV. This suggests that Irgb6 has a role as a pioneer in the process by which multiple IRG proteins access the PV. Irgb6-deficient mice are highly susceptible to infection by a strain of T. gondii avirulent in wild-type mice.

Cytoplasmic dsRNA induces the expression of OCT3/4 and NANOG mRNAs in differentiated human cells.

Cytoplasmic dsRNA is recognized by RNA helicase RIG-I (RIG-I) and melanoma differentiation-associated protein 5 (MDA5), triggering induction of the innate immune response via the mitochondrial antiviral signaling protein (MAVS). In contrast, extracellular dsRNA is internalized into endosomes and recognized by Toll-like receptor 3 (TLR3), which triggers signaling via the Toll-like receptor adaptor molecule 1 (TICAM-1). Poly(I:C) is a synthetic dsRNA analog and increases the expression of octamer-binding protein 3/4 (OCT3/4), NANOG, and SRY-box (SOX) mRNAs during pluripotency induction. However, the mechanism underlying this increase is unclear. Here, we focused on the mechanism of poly(I:C)-induced expression of stem cell-specific genes in human somatic cells. Addition of poly(I:C) to human fibroblast culture medium did not increase OCT3/4 mRNA expression, but poly(I:C) transfection markedly increased OCT3/4 expression and induced nuclear localization of the OCT3/4 protein, implying that not TLR3, but RIG-I and MDA5 are required for OCT3/4 expression. Moreover, although cytoplasmic dsRNA increased OCT3/4 mRNA, cytoplasmic dsDNAs, such as salmon sperm DNA and poly(dA:dT), did not. Interestingly, the expression of NANOG, SOX2, Krüppel-like factor 4 (KLF4), and proto-oncogene c-Myc was also increased by cytoplasmic dsRNA. Of note, siRNAs that silenced MAVS and interferon regulatory factor 1 (IRF1) expression reduced OCT3/4 levels after stimulation with poly(I:C); however, an NF-κB inhibitor and siRNA-mediated knockdown of proto-oncogene c-Jun did not significantly reduce the mRNA levels. We conclude that cytoplasmic dsRNA increases the expression of stem cell-specific genes in human somatic cells in a MAVS- and IRF1-dependent manner.

Attenuation of the Innate Immune Response against Viral Infection Due to ZNF598-Promoted Binding of FAT10 to RIG-I.

Excessive innate immune response is harmful to the host, and aberrant activation of the cytoplasmic viral RNA sensors RIG-I and MDA5 leads to autoimmune disorders. ZNF598 is an E3 ubiquitin ligase involved in the ribosome quality control pathway. It is also involved in the suppression of interferon (IFN)-stimulated gene (ISG) expression; however, its underlying mechanism is unclear. In this study, we show that ZNF598 is a negative regulator of the RIG-I-mediated signaling pathway, and endogenous ZNF598 protein binds to RIG-I. ZNF598 ubiquitin ligase activity is dispensable for the suppression of RIG-I signaling. Instead, ZNF598 delivers a ubiquitin-like protein FAT10 to the RIG-I protein, resulting in the inhibition of RIG-I polyubiquitination, which is required for triggering downstream signaling to produce type I IFN. Moreover, ZNF598-mediated suppression is abrogated by FAT10 knockout. Our data elucidate the mechanism by which ZNF598 inhibits RIG-I-mediated innate immune response.

MicroRNA-451a in extracellular, blood-resident vesicles attenuates macrophage and dendritic cell responses to influenza whole-virus vaccine.

The innate immune system is important for the efficacy of vaccines, but excessive innate immune responses can cause adverse reactions after vaccination. Extracellular vesicles (EVs) are enriched in the blood and can deliver functional RNAs, such as microRNAs (miRNAs), to recipient cells, thereby mediating intercellular communication. However, the role of EVs in controlling the innate immune responses to vaccines has not been fully elucidated. Here, we found that miR-451a is abundant in human serum EVs and that its presence in blood-circulating EVs affects the innate immune responses of macrophages and dendritic cells to inactivated whole-virus vaccines (WV) against influenza. miR-451a in human serum EVs was stable for a week in healthy subjects, and its levels gradually fluctuated over several months. miR-451a within serum EVs was internalized into serum-cultured macrophages and dendritic cells and reduced endogenous 14-3-3ζ protein levels and decreased the expression of type I IFN and interleukin 6 in response to WV stimulation. miR-451a levels in blood-circulating EVs were positively correlated with intracellular miR-451a levels in mouse splenic CD11c+ cells and inversely correlated with the innate immune response to inactivated WV in vivo These findings suggest that miR-451a in circulating EVs is internalized into recipient cells in vivo and that this internalization results in an attenuation of the innate immune response to WV. Moreover, a microarray analysis identified several other miRNAs that affect the macrophage response to inactivated WV. Our results reveal that miRNAs in circulating EVs significantly modify the responses of macrophages and dendritic cells to inactivated WV.

Activation of TLR3 and its adaptor TICAM-1 increases miR-21 levels in extracellular vesicles released from human cells.

Pattern-recognition receptors (PRRs) recognizes viral RNAs and trigger the innate immune responses. Toll-like receptor 3 (TLR3), a PRR, recognizes viral double-stranded RNA (dsRNA) in endolysosomes, whereas cytoplasmic dsRNA is sensed by another PRR, MDA5. TLR3 and MDA5 utilize TICAM-1 and MAVS, respectively, to trigger the signal for inducing innate immune responses. Extracellular vesicles (EVs) include the exosomes and microvesicles; an accumulating body of evidence has shown that EVs delivers functional RNA, such as microRNAs (miRNAs), to other cells and thus mediate intercellular communications. Therefore, EVs carrying miRNAs affect innate immune responses in macrophages and dendritic cells. However, the mechanism underlying the regulation of miRNA levels in EVs remains unclear. To elucidate the mechanism, we sought to reveal the pathway that control miRNA expression levels in EVs. Here, we found that TLR3 stimulation increased miR-21 levels in EVs released from various types of human cells. Ectopic expression of the TLR3 adaptor, TICAM-1, increased miR-21 levels in EVs but not intracellular miR-21 levels, suggesting that TICAM-1 augmented sorting of miR-21 to EVs. In contrast, the MDA5 adaptor, MAVS, did not increase miR-21 levels in EVs. The siRNA for TICAM-1 reduced EV miR-21 levels after stimulation of TLR3. Collectively, our data indicate a novel role of the TLR3-TICAM-1 pathway in controlling miR-21 levels in EVs.

Aureobasidium pullulans-cultured fluid induces IL-18 production, leading to Th1-polarization during influenza A virus infection.

Several microbial molecules with pathogen-associated molecular patterns stimulate host innate immune responses. The innate immune system plays a crucial role in activating acquired immune response via cytokine production and antigen presentation. Previous studies have shown that Aureobasidium pullulans-cultured fluid (AP-CF), which contains ß-glucan, exhibits adjuvant activity and renders mice resistance to influenza A virus infection; however, the underlying mechanism remains elusive. In this study, we investigated the innate immune response to AP-CF. We found that intraperitoneal administration of AP-CF increased the serum level of IL-18 and the number of splenic IFN-γ producing CD4+ cells during influenza A virus infection. The adjuvant effect of AP-CF was distinct from that of alum, which is known to have the ability to stimulate a Th2 immune response. In addition, AP-CF injection barely increased the number of peritoneal neutrophils and inflammatory macrophages, whereas alum injection markedly increased the number of neutrophils and inflammatory macrophages, suggesting that AP-CF is a weak inducer of inflammation compared to alum. AP-CF induced IL-18 production by DC2.4 cells, a dendritic cell line, and by peritoneal exudate cells that include peritoneal macrophages. Collectively, our findings indicate that AP-CF is an adjuvant that promotes the Th1 response during influenza A virus infection.

Characterization of specimens obtained by different sampling methods for evaluation of periodontal bacteria.

Quantitative analysis of periodontal bacteria is considered useful for clinical diagnosis, evaluation and assessment of the risk of periodontal disease. The purpose of this study was to compare the effectiveness of sampling of saliva, supragingival and subgingival plaque for evaluation of periodontal bacteria. From each of 12 subjects, i) subgingival plaque was collected from the deepest pocket using a sterile paper point, ii) stimulated whole saliva was collected after chewing gum, and iii) supragingival plaque was collected using a tooth brush. These samples were sent to the medical examination laboratory for quantitative analysis of the counts of three periodontal bacterial species: Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia. The proportions of these bacteria in subgingival plaque were higher than those in saliva or supragingival plaque, but lower in subgingival plaque than in saliva or supragingival plaque. In several cases, periodontal bacteria were below the levels of detection in subgingival plaque. We concluded that samples taken from subgingival plaque may be more useful for evaluating the proportion of periodontal bacteria in deep pockets than is the case for other samples. Therefore, for evaluation of periodontal bacteria, clinicians should consider the characteristics of the specimens obtained using different sampling methods.

Zyxin stabilizes RIG-I and MAVS interactions and promotes type I interferon response.

RIG-I and MDA5 are cytoplasmic viral RNA sensors that belong to the RIG-I-like receptors (RLRs), which induce antiviral innate immune responses, including the production of type I interferon and other pro-inflammatory cytokines. After recognition of viral RNA, the N-terminal caspase activation and recruitment domains (CARDs) of RIG-I and MDA5 bind to a CARD in the MAVS adaptor molecule, resulting in MAVS oligomerization and downstream signaling. To reveal the molecular mechanism of MAVS-dependent signaling, we performed a yeast two-hybrid screening and identified zyxin as a protein that binds to MAVS. Zyxin co-immunoprecipitated with MAVS in human cells. A proximity ligation assay showed that zyxin and MAVS partly co-localized on mitochondria. Ectopic expression of zyxin augmented MAVS-mediated IFN-ß promoter activation, and knockdown of zyxin (ZYX) attenuated the IFN-ß promoter activation. Moreover, ZYX knockdown reduced the expression of type I IFN and an interferon-inducible gene after stimulation with polyI:C or influenza A virus RNA. Interestingly, physical interactions between RLRs and MAVS were abrogated by ZYX knockdown. These observations indicate that zyxin serves as a scaffold for the interactions between RLRs and MAVS.

Recognition of Viral RNA by Pattern Recognition Receptors in the Induction of Innate Immunity and Excessive Inflammation During Respiratory Viral Infections.

The innate immune system is the first line of defense against virus infection that triggers the expression of type I interferon (IFN) and proinflammatory cytokines. Pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns, resulting in the induction of innate immune responses. Viral RNA in endosomes is recognized by Toll-like receptors, and cytoplasmic viral RNA is recognized by RIG-I-like receptors. The host innate immune response is critical for protection against virus infection. However, it has been postulated that an excessive inflammatory response in the lung caused by the innate immune response is harmful to the host and is a cause of lethality during influenza A virus infection. Although the deletion of genes encoding PRRs or proinflammatory cytokines does not improve the mortality of mice infected with influenza A virus, a partial block of the innate immune response is successful in decreasing the mortality rate of mice without a loss of protection against virus infection. In addition, morbidity and mortality rates are influenced by other factors. For example, secondary bacterial infection increases the mortality rate in patients with influenza A virus and in animal models of the disease, and environmental factors, such as cigarette smoke and fine particles, also affect the innate immune response. In this review, we summarize recent findings related to the role of PRRs in innate immune response during respiratory viral infection.

Chair-side detection of Prevotella Intermedia in mature dental plaque by its fluorescence.

BACKGROUND: Prevotella intermedia/nigrescens is one of the well-known pathogens causing periodontal diseases, and the red florescence excited by the visible blue light caused by the protoporphyrin IX in the bacterial cells could be useful for the chair-side detection. The aim of this study was to evaluated levels of periodontal pathogen, especially P. intermedia in clinical samples of red fluorescent dental plaque. METHODS: Thirty two supra gingival plaque samples from six individuals were measured its fluorescence at 640nm wavelength excited by 409nm. Periodontopathic bacteria were counted by the Invader PLUS PCR assay. Co-relations the fluorescence intensity and bacterial counts were analyzed by Person's correlation coefficient and simple and multiple regression analysis. Positive and negative predictive values of the fluorescence intensities for with or without P. intermedia in supragingival plaque was calculated. RESULTS: When relative fluorescence unit (RFU) were logarithmic transformed, statistically significant linear relations between RFU and bacterial counts were obtained for P. intermedia, Porphyromonas gingivalis and Tannerella forsythia. By the multiple regression analysis, only P. intermedia had statistically significant co-relation with fluorescence intensities. All of the fluorescent dental plaque contained P. intermedia m. In contrast, 28% of non-fluorescent plaques contained P. intermedia. CONCLUSION: To check the fluorescence dental plaque in the oral cavity could be the simple chair-side screening of the mature dental plaque before examining the periodontal pathogens especially P. intermedia by the PCR method.

Extracellular Vesicles Deliver Host and Virus RNA and Regulate Innate Immune Response.

The innate immune system plays a crucial role in controlling viral infection. Pattern recognition receptors (PRRs), such as Toll-like receptors and RIG-I-like receptors, sense viral components called pathogen-associated molecular patterns (PAMPs) and trigger signals to induce innate immune responses. Extracellular vesicles (EVs), including exosomes and microvesicles, deliver functional RNA and mediate intercellular communications. Recent studies have revealed that EVs released from virus-infected cells deliver viral RNA to dendritic cells and macrophages, thereby activating PRRs in recipient cells, which results in the expression of type I interferon and pro-inflammatory cytokines. On the other hand, EVs transfer not only viral RNA but also host microRNAs to recipient cells. Recently, infection of hepatocytes with hepatitis B virus (HBV) was shown to affect microRNA levels in EVs released from virus-infected cells, leading to attenuation of host innate immune response. This suggests that the virus utilizes the EVs and host microRNAs to counteract the antiviral innate immune responses. In this review, we summarize recent findings related to the role of EVs in antiviral innate immune responses.

Regulation of RIG-I Activation by K63-Linked Polyubiquitination.

RIG-I is a pattern recognition receptor and recognizes cytoplasmic viral double-stranded RNA (dsRNA). Influenza A virus, hepatitis C virus, and several other pathogenic viruses are mainly recognized by RIG-I, resulting in the activation of the innate immune responses. The protein comprises N-terminal two caspase activation and recruitment domains (2CARDs), an RNA helicase domain, and the C-terminal domain (CTD). The CTD recognizes 5'-triphosphate viral dsRNA. After recognition of viral dsRNA, the protein harbors K63-linked polyubiquitination essential for RIG-I activation. First, it was reported that TRIM25 ubiquitin ligase delivered K63-linked polyubiquitin moiety to the 2CARDs. The polyubiquitin chain stabilizes a structure called the 2CARD tetramer, in which four 2CARDs assemble and make a core that promotes the aggregation of the mitochondrial antiviral-signaling (MAVS) protein on mitochondria. MAVS aggregation then triggers the signal to induce the innate immune responses. However, subsequent studies have reported that Riplet, MEX3C, and TRIM4 ubiquitin ligases are also involved in K63-linked polyubiquitination and the activation of RIG-I. MEX3C and TRIM4 mediate polyubiquitination of the 2CARDs. By contrast, Riplet ubiquitinates the CTD. The physiological significance of each ubiquitin ligases has been shown by knockout and knockdown studies, but there appears to be contradictory to evidence reported in the literature. In this review, we summarize recent findings related to K63-linked polyubiquitination and propose a model that could reconcile current contradictory theories. We also discuss the physiological significance of the ubiquitin ligases in the immune system against viral infection.

Complete genome sequence of Streptococcus troglodytae TKU31 isolated from the oral cavity of a chimpanzee (Pan troglodytes).

Streptococcus troglodytae TKU31 was isolated from the oral cavity of a chimpanzee (Pan troglodytes) and was found to be the most closely related species of the mutans group streptococci to Streptococcus mutans. The complete sequence of TKU31 genome consists of a single circular chromosome that is 2,097,874 base pairs long and has a G + C content of 37.18%. It possesses 2082 coding sequences (CDSs), 65 tRNAs and five rRNA operons (15 rRNAs). Two clustered regularly interspaced short palindromic repeats, six insertion sequences and two predicted prophage elements were identified. The genome of TKU31 harbors some putative virulence associated genes, including gtfB, gtfC and gtfD genes encoding glucosyltransferase and gbpA, gbpB, gbpC and gbpD genes encoding glucan-binding cell wall-anchored protein. The deduced amino acid identity of the rhamnose-glucose polysaccharide F gene (rgpF), which is one of the serotype determinants, is 91% identical with that of S. mutans LJ23 (serotype k) strain. However, two other virulence-associated genes cnm and cbm, which encode the collagen-binding proteins, were not found in the TKU31 genome. The complete genome sequence of S. troglodytae TKU31 has been deposited at DDBJ/European Nucleotide Archive/GenBank under the accession no. AP014612.