Microbiology and Immunology最新文献

Streptococcus pyogenes displays a wide variety of pili, which is largely dependent on serotype. A distinct subset of S. pyogenes strains that possess the Nra transcriptional regulator demonstrates thermoregulated pilus production. Findings obtained in the present study of an Nra-positive serotype M49 strain revealed involvement of conserved virulence factor A (CvfA), also referred to as ribonuclease Y (RNase Y), in virulence factor expression and pilus production, while a cvfA deletion strain showed reduced pilus production and adherence to human keratinocytes as compared with wild-type and revertant strains. Furthermore, transcript levels of pilus subunits and srtC2 genes were decreased by cvfA deletion, which was remarkable at 25°C. Likewise, both messenger RNA (mRNA) and protein levels of Nra were remarkably decreased by cvfA deletion. Whether the expression of other pilus-related regulators, including fasX and CovR, was subject to thermoregulation was also examined. While the mRNA level of fasX, which inhibits cpa and fctA translation, was decreased by cvfA deletion at both 37°C and 25°C, CovR mRNA and protein levels, as well as its phosphorylation level were not significantly changed, suggesting that neither fasX nor CovR is necessarily involved in thermosensitive pilus production. Phenotypic analysis of the mutant strains revealed that culture temperature and cvfA deletion had varied effects on streptolysin S and SpeB activities. Furthermore, bactericidal assay data showed that cvfA deletion decreased the rate of survival in human blood. Together, the present findings indicate that CvfA is involved in regulation of pilus production and virulence-related phenotypes of the serotype M49 strain of S. pyogenes.

Cover photograph: (1) The role of γδ T cells in skin is still unknown. Do they interact with sporozoite? Do they able to kill sporozoite or facilitate DC to recognize and phagocytize sporozoite? Lots to be answered in the future. (2) The responses of γδ T cells during liver-stage are mainly protective. Studies of attenuated sporozoite vaccination showed activation and expansion of γδ T cells. These γδ T cells produce large amount of IFN-γ and were able to protect subsequent challenge infection in human. γδ T cells are involved in activation and maturation of DC, and they may facilitate recruitment of inflammatory cells in the liver. γδ T cells also contribute to the activation and accumulation of CD8+ T cells directly or through DC. (3) Protective and pathogenic roles of γδ T cells during blood-stage have been proposed. Upon activation γδ T cells produce pro-inflammatory cytokines which enhance APC cells maturation. Also they are involved in accumulation and activation of myeloid cells by producing M-CSF. They can present antigens to naïve γδ T cells and initiate adaptive immune response. Moreover, γδ T cells facilitate antibody production and germinal center formation either directly contacting with B cells or through T follicular helper cells. In vitro studies of human γδ T cells showed capacity of antigen presentation, phagocytosis and cytotoxicity. However, these functions should be investigated in the tissue or in vivo. Microbiol Immunol: 67:239–247. Article link here

Human herpesvirus 8 (HHV8; also known as Kaposi's sarcoma-associated herpesvirus [KSHV]) utilizes the viral E3 ubiquitin ligase family members K3 and K5 for immune evasion. Both K3 and K5 mediate the ubiquitination of host MHC class I (MHC-I) molecules, which play a key role in antigen presentation to cytotoxic T lymphocytes (CTLs). Because ubiquitinated MHC-I is immediately down-regulated from the cell surface, HHV8-infected cells can escape surveillance by CTLs. K3 and K5 have similar domain structures and topologies. They contain an N-terminal RINGv ubiquitin ligase domain, two transmembrane helices, and an intrinsically disordered cytoplasmic tail at the C-terminus. The cytoplasmic tail contains a membrane-proximal “conserved region” involved in ligase activity. On the other hand, the role of the membrane-distal region of the cytoplasmic tail, termed the “C-tail” in this study, remains unclear. Here, we demonstrate that the C-tail contributes to the protein expression of both K3 and K5. The C-tail-truncated K3 and K5 mutants were rapidly reduced in cells. The recombinant C-tail proteins bind to acidic lipids via a basic charge cluster located near the C-terminus of the C-tails. Similar to the C-tail-truncated mutants, the basic charge cluster-substituting mutants showed decreased protein expression of K3 and K5. These findings suggest that the basic charge cluster near the C-terminus of the cytoplasmic tail contributes to the molecular stability of K3 and K5.

Cover photograph: Location of missense mutation associated with chronic granulomatous disease within the Nox2-p22phox heterodimer. Microbiol Immunol: 67:194–200. Article link here

Many Rickettsia species of the spotted fever group (SFG) cause tick-borne diseases known as “spotted fever.” One of the candidate SFG Rickettsia species is “Candidatus Rickettsia kotlanii,” which was first detected in Haemaphysalis concinna in Hungary in 2006. However, its precise phylogenetic position in the SFG is not clear because only single-gene sequence–based phylogenetic analyses were performed using very limited genes. Here, we present the complete genome sequences of two Japanese “Ca. R. kotlanii” isolates, which differed only by a 135 bp insertion/deletion (InDel). Using these genomes and publicly available whole genome sequences of other Rickettsia species, the precise phylogenetic position of “Ca. R. kotlanii” in Rickettsia was determined to be in a clade of the SFG. The phylogenetic relationships and average nucleotide identity of “Ca. R. kotlanii” relative to the other species indicated that “Ca. R. kotlanii” is an independent taxon in the SFG. Notably, although the genomes of the two isolates were almost identical, the isolates were obtained from different tick species in different regions and years, suggesting extremely low genomic diversity in “Ca. R. kotlanii.” While the genome of “Ca. R. kotlanii” is the smallest in the transitional group and SFG Rickettsia sequenced to date, we identified genes uniquely present or absent in “Ca. R. kotlanii,” but most were apparently degraded. Therefore, analyses of differences at the sequence (single nucleotide polymorphisms and small InDels) or gene expression level will be required to understand the functional or physiological features unique to “Ca. R. kotlanii.”

Immune checkpoint inhibitors (ICIs) have recently improved the prognosis of various cancers. By contrast, some immune-related adverse events (irAEs) caused by ICIs are fatal and have become problematic. The pathogenesis of irAEs remains unknown and must be elucidated to establish biomarkers. This study investigated plasma cytokine, chemokine, and anti-CD74 autoantibody levels in patients with renal cell carcinoma (RCC) and analyzed their association with irAEs. In a discovery cohort of 13 patients, plasma levels of chemokine (C–X–C motif) ligand (CXCL) 1, IL-17A, IL-1β, IL-6, IL-8, CXCL10, MCP-1, and TNFα were measured at baseline and post–dose 1. Only CXCL10, at post–dose 1 but not at baseline, was significantly associated with grade 2 or higher irAEs (P = 0.0413). Plasma CXCL10 levels were then measured at baseline and post–dose 1 in an extended cohort of 43 patients with RCC who received ICI-based treatment. Higher plasma CXCL10 levels both at baseline and post–dose1 were significantly associated with the occurrence of grade 2 or higher irAEs (P = 0.0246 and 0.0137, respectively). Plasma CXCL13 levels, which we measured in a previous study, were significantly higher in patients with grade 2 or higher irAEs at baseline but not at post–dose 1 (P = 0.0037 and 0.052, respectively). No significant association between plasma anti-CD74 autoantibody level and both irAE pneumonitis and any grade 2 or higher irAE was observed. In conclusion, plasma CXCL10 is significantly associated with the occurrence of irAEs in patients with RCC treated with ICIs. CXCL10 is a potential predictive and on-treatment biomarker for irAEs.

Bordetella pertussis causes pertussis, which is characterized by paroxysmal coughing. This disease is generally prevented through vaccination; however, the number of pertussis cases is increasing worldwide despite high vaccination coverage. We previously reported that an autotransporter of B. pertussis, virulence-associated gene 8 (Vag8), causes coughing in combination with pertussis toxin and lipooligosaccharide. Here, we show that immunization with Vag8 protected mice from coughing after B. pertussis infection and enhanced the efficacy of a current pertussis vaccine containing pertussis toxoid against the cough. Our findings indicate that Vag8 could be a vaccine antigen to prevent pertussis cough.

Human cytomegalovirus (HCMV) infection of monocytes results in the production of inflammatory cytokine through inflammasome. However, the mechanism of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation in HCMV infection remains unclear. In this study, HCMV infection promoted the increase of mitochondrial fusion and caused mitochondrial dysfunction in THP-1 cells, including excessive reactive oxygen species production and decreased mitochondrial membrane potential (Δψm). Meanwhile, the expression of mitochondrial DNA (mtDNA)-binding protein TFAM (transcription factor A, mitochondrial) was decreased and mtDNA content in the cytoplasm was increased. Knockdown of TFAM caused an increase in mtDNA copy number in the cytoplasm and resulted in elevated NLRP3 expression, active caspase-1, and mature IL-1β. After a 3 h treatment with MCC950, an NLRP3 inhibitor, the increase of cleaved caspase-1 and mature IL-1β were suppressed. Besides, overexpression of TFAM inhibited the expression of NLRP3, cleaved caspase-1, and mature IL-1β. In addition, knockdown of NLRP3 inhibited the IL-1β process after HCMV infection. mtDNA-deficient cells showed a limited ability to produce NLRP3 and process IL-1β after HCMV infection. In conclusion, HCMV infection of THP-1 cells resulted in decreased mitochondrial TFAM protein expression and increased mtDNA release into the cytoplasm, which eventually led to the activation of NLRP3 inflammasome.

Hepatitis B virus (HBV) is a leading cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Current therapeutic drugs for chronic HBV infection use IFN and nucleos(t)ide analogs; however, their efficacy is limited. Thus, there is an urgent need to develop new antivirals for HBV therapy. In this study, we identified a plant-derived polyphenolic bioflavonoid, amentoflavone, as a new anti-HBV compound. Amentoflavone treatment dose-dependently inhibited HBV infection in HBV-susceptible cells with HepG2-hNTCP-C4 and primary human hepatocyte PXB-cells. A mode-of-action study showed that amentoflavone inhibits the viral entry step, but not the viral internalization and early replication processes. Attachment of HBV particles as well as HBV preS1 peptide to HepG2-hNTCP-C4 cells was inhibited by amentoflavone. The transporter assay revealed that amentoflavone partly inhibits uptake of sodium taurocholate cotransporting polypeptide (NTCP)–mediated bile acid. Furthermore, effect of various amentoflavone analogs on HBs and HBe production from HBV-infected HepG2-hNTCP-C4 cells was examined. Robustaflavone exhibited comparable anti-HBV activity to that of amentoflavone and an amentoflavone-7,4', 4‴-trimethyl ether derivative (sciadopitysin) with moderate anti-HBV activity. Cupressuflavone or the monomeric flavonoid apigenin did not exhibit the antiviral activity. Amentoflavone and its structurally related biflavonoids may provide a potential drug scaffold in the design of a new anti-HBV drug inhibitor targeting NTCP.

Dendritic cells (DCs) take up antigens derived from pathogens such as bacteria and viruses, and from tumor cells and induce the activation of antigen-specific T cells through major histocompatibility complex (MHC)-mediated antigen presentation. Mainstream cigarette smoke extract (CSE) has various effects, and the effects of its major components, nicotine and tar, have been analyzed extensively. Recently, the physiological effects of nicotine- and tar-removed CSE (cCSE) have also been reported. However, the effects of cCSE on DC-mediated immune responses remain unknown. In this study, we found that cCSE enhanced lipopolysaccharide (LPS)-stimulated induction of the expression of MHC-I and MHC-II on the cell surface of mouse bone marrow-derived DCs (BMDCs). In contrast, cCSE suppressed the induction of CD86 induced by stimulation with curdlan and interferon-γ (IFN-γ). In addition, cCSE suppressed the production of IL-12, IL-23, and IL-10 by LPS and curdlan stimulation. In the presence of cCSE, LPS-stimulated BMDCs showed enhanced activation of CD4 and CD8 T cells and increased IL-2 production from T cells by antigen presentation in a mixed-leukocyte reaction assay. In contrast, cCSE did not affect the activation of T cells by curdlan- or IFN-γ-stimulated BMDCs, and curdlan-stimulated BMDCs suppressed IL-17 production from T cells and enhanced IFN-γ production. These results suggest that cCSE has different effects on the activation signals induced by LPS, curdlan, and IFN-γ in BMDCs and modulates the antigen presentation function of BMDCs.