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Maezono Keisuke

Faculty of Veterinary Medicine　Veterinary Medicine　Preventive Veterinary MedicineAssistant Professor
International Institute for Zoonosis ControlAssistant Professor

Researcher basic information

■ Degree
  • 学士（獣医学）, Mar. 2021
■ URL
researchmap URLホームページURL■ Various IDs
Researcher number
  • 61008497
ORCID IDJ-Global ID■ Educational Organization

Career

■ Career
Career
  • Jun. 2024 - Present
    北海道大学 大学院獣医学研究院 獣医学部門 衛生学分野 公衆衛生学教室, 助教
  • Apr. 2024 - Mar. 2026
    Japan Society for the Promotion of Science, 特別研究員DC2
  • Apr. 2021 - Mar. 2022
    Morinaga Milk Industry Co., Ltd., 研究本部
Educational Background
  • Apr. 2022 - May 2024, Hokkaido University, 大学院獣医学研究院
  • Apr. 2015 - Mar. 2021, Hokkaido University, School of Veterinary Medicine

Research activity information

■ Papers
  • Maintenance of Hokkaido virus, a genotype of Orthohantavirus puumalaense, in the rodent host Myodes rufocanus bedfordiae under natural conditions.
    Thi Ngoc Thuy Duong; Michihito Sasaki; Yasuko Orba; Keisuke Aoshima; Osamu Ichii; Keisuke Maezono; Passawat Thammahakin; Haruto Eguchi; Shintaro Kobayashi; Hiroaki Kariwa
    Journal of virology, 100, 7, e0032126, 21 Jul. 2026, [International Magazine]
    English, Scientific journal, UNLABELLED: A variety of orthohantaviruses (family Hantaviridae) have preferred natural host species, with transmission among hosts generally thought to occur through direct physical contact and inhalation of virus-contaminated excreta, although the infection to the other species occasionally occurs. Despite extensive experimental studies, the mechanisms of orthohantavirus maintenance and transmission under natural conditions remain unclear. In this study, field surveys were conducted in a forest in Tobetsu, Hokkaido, Japan, between 2022 and 2025 to capture gray red-backed voles (Myodes rufocanus bedfordiae), the natural host of Hokkaido virus (HOKV), a genotype of Orthohantavirus puumalaense. Among 199 captured rodents, 23 were positive for HOKV infection. Five individuals were positive for viral RNA but negative for anti-HOKV IgG antibodies on ELISA and IFA and exhibited low neutralizing antibody titers and low IgG avidity indexes (≤26%), suggesting acute infection. In contrast, 18 individuals were positive for viral RNA and showed high antibody titers on ELISA, IFA, and neutralization tests, as well as high IgG avidities (≥64%); these individuals were considered persistently infected. High levels of viral RNA and antigens were consistently detected in the lungs, kidneys, and spleen during both potential acute and persistent phases of HOKV infection by quantitative PCR and immunohistochemistry. Infectious HOKV was also recovered from oral swabs (8/8), urine (3/6), and feces (4/6) of individual rodents captured in 2024. These findings showed that HOKV can persist at high viral loads in host organs and be excreted throughout the course of infection, contributing to the long-term maintenance of orthohantavirus in natural host populations. IMPORTANCE: Diseases caused by zoonotic agents are major public health concerns. Orthohantaviruses are typical examples of zoonotic viruses transmitted from wild rodent hosts. Despite extensive laboratory investigations, the mechanisms of viral persistence and transmission in natural hosts remain poorly understood. Our study demonstrated that Hokkaido virus (HOKV), a genotype of Orthohantavirus puumalaense, seems to establish both acute and persistent infections in wild grey red-backed voles (Myodes rufocanus bedfordiae) without inducing major pathological changes. Detection of infectious virus in saliva, urine, and feces revealed multiple virus-shedding routes. Saliva likely serves as the predominant source of transmission, given that infectious virus was recovered from oral swabs of all infected rodents captured in 2024. These findings expand understanding of orthohantavirus ecology, persistence, and maintenance in reservoir populations. This information is crucial for evaluating spillover risks and enhancing public health preparedness.
  • The ER-Resident Protein PDZD8 Inhibits Virus Production of West Nile Virus.
    Shiori Abe; Akari Sato; Haruto Eguchi; Keisuke Maezono; Passawat Thammahakin; Duong Thi Ngoc Thuy; Hiroaki Kariwa; Shintaro Kobayashi
    Microbiology and immunology, 29 Jun. 2026, [International Magazine]
    English, Scientific journal, West Nile virus (WNV) remodels the endoplasmic reticulum (ER) membrane in cells to aid virus production. However, the molecular mechanisms underlying this process remain unclear. PDZD8 is an ER-resident protein that mediates ER-mitochondria contact and lipid transfer, both of which are associated with membrane remodeling. In this study, we found that WNV infection suppressed the expression of PDZD8, leading to a reduction in ER-mitochondria contact sites. By contrast, PDZD8 suppressed WNV production by inhibiting the processes of viral particle assembly and release. These findings suggest that WNV suppresses PDZD8 expression to partially counteract its inhibitory effect on WNV production.
  • Tick saliva reprograms macrophages into immunosuppressive hubs that regulate T-cell immunity in Rhipicephalus microplus infestation.
    Hayato Nakamura; Tomohiro Okagawa; Naoya Maekawa; Luís Fernando Parizi; Mari Ikehata; Wisa Tiyamanee; Shwe Yee Win; Hiroto Takeuchi; Keisuke Maezono; Passawat Thammahakin; Shintaro Kobayashi; Mizuki Fukuta; Minato Hirano; Kentaro Yoshii; Shiro Murata; Kazuhiko Ohashi; Carlos Logullo; Itabajara da Silva Vaz Jr; Satoru Konnai
    Communications biology, 9, 1, 30 Apr. 2026, [International Magazine]
    English, Scientific journal, Ticks transmit diverse pathogens and secrete saliva with immunomodulatory properties that facilitates blood feeding. However, the cellular mechanisms underlying saliva-mediated immune suppression remain poorly defined. Here, we identify macrophages as the central hub through which saliva from the cattle tick Rhipicephalus microplus suppresses T-cell mediated immunity. Tick saliva inhibited IFN-γ and TNF production by CD4⁺ and CD8⁺ T cells while enhancing IL-10 and TGF-β expression, particularly in regulatory T cells. These effects were lost upon removal of CD14⁺ cells, underscoring the importance of macrophage-lineage cells in saliva-induced immunosuppression. Transcriptomic and functional analyses showed that tick saliva reprograms macrophages into an immunosuppressive state with reduced MHC class II, attenuated proinflammatory signaling, and suppressed chemokine production. Consistent with these findings, immunofluorescence analysis of tick-feeding sites showed an increased presence of IL-10-expressing macrophages and T cells. Our findings highlight a strategy by which arthropod saliva suppresses host immunity to facilitate pathogen transmission.
  • Exhausted CD4+T cells are associated with CCL4-driven immunosuppressive macrophage accumulation in enzootic bovine leukosis.
    Hayato Nakamura; Tomohiro Okagawa; Malik Hamaïdia; Wisa Tiyamanee; Mari Ikehata; Minagi Hirose; Maho Inoue; Luc Willems; Keisuke Maezono; Passawat Thammahakin; Shintaro Kobayashi; Yukinari Kato; Yasuhiko Suzuki; Naoya Maekawa; Shiro Murata; Kazuhiko Ohashi; Satoru Konnai
    Frontiers in immunology, 17, 1808815, 1808815, 2026, [International Magazine]
    English, Scientific journal, In enzootic bovine leukosis (EBL), a B-cell lymphoma caused by bovine leukemia virus (BLV) infection, immune remodeling within tumor-affected lymph nodes is currently poorly understood. Here, we analyzed chemokine production and macrophage phenotypes in tumor-affected lymph nodes in EBL, focusing on CCL4. Intracellular cytokine staining revealed that, compared with healthy lymph nodes, EBL tumor-affected lymph nodes showed increased proportions of CCL4 expressing cells, particularly among CD4+ T cells and B cells. Functional migration assays showed that recombinant CCL4 induced robust monocyte migration, with a comparatively modest T-cell migration. To identify lymph node macrophages, we characterized CD11bhiCD172a+ cells and confirmed their macrophage identity based on high expression levels of CD11c, CD14, CD16, and CD68. Using this definition, we found that the CD11bhiCD172a+ population was markedly increased in tumor-affected lymph nodes. Phenotypic analysis revealed an increased proportion of CD163+ and CD163+PD-L1+ macrophages, consistent with the acquisition of an immunosuppressive phenotype. In parallel, macrophages in tumor-affected lymph nodes showed a shift from MHC class I/IIhi to MHC I/IIlo subsets and reduced co-expression of MHC molecules with CD80 and CD86, indicating impaired antigen-presenting features. Collectively, these findings suggest that elevated CCL4 production in tumor lesions induced by EBL is associated with monocyte recruitment and the accumulation of phenotypically altered macrophages, highlighting a chemokine-driven remodeling of the tumor immune microenvironment.
  • Molecular evolution of Hokkaido virus, a genotype of Orthohantavirus puumalaense, among Myodes rodents.
    Duong Thi Ngoc Thuy; Michihito Sasaki; Yasuko Orba; Passawat Thammahakin; Keisuke Maezono; Shintaro Kobayashi; Hiroaki Kariwa
    Virology, 597, 110168, 110168, Sep. 2024, [International Magazine]
    English, Scientific journal, Viruses in the genus Orthohantavirus within the family Hantaviridae cause human hantavirus infections and represent a threat to public health. Hokkaido virus (HOKV), a genotype of Orthohantavirus puumalaense (Puumala virus; PUUV), was first identified in Tobetsu, Hokkaido, Japan. Although it is genetically related to the prototype of PUUV, the evolutionary pathway of HOKV is unclear. We conducted a field survey in a forest in Tobetsu in 2022 and captured 44 rodents. Complete coding genome sequences of HOKVs were obtained from five viral-RNA-positive rodents (four Myodes rufocanus bedfordiae and one Apodemus speciosus). Phylogenetic analysis revealed a close relationship between the phylogenies and geographical origins of M. rufocanus-related orthohantaviruses. Comparison of the phylogenetic trees of the S segments of orthohantaviruses and the cytochrome b genes of Myodes species suggested that Myodes-related orthohantaviruses evolved in Myodes rodent species as a result of genetic isolation and host switching.
  • Rab27a promotes degradation of West Nile virus E protein in the lysosome.
    Shintaro Kobayashi; Seira Kawai; Yukine Fukuda; Haruto Eguchi; Keisuke Maezono; Passawat Thammahakin; Hirofumi Sawa; Hiroaki Kariwa
    iScience, 27, 4, 109539, 109539, 19 Apr. 2024, [International Magazine]
    English, Scientific journal, Rab27a, a Rab family small GTPases, plays an important role in the trafficking and secretion of the intracellular proteins and has been reported to promote various viral multiplication. However, whether Rab27a is involved in West Nile virus (WNV) multiplication is unknown. This study examined the ability of Rab27a to suppress WNV multiplication. The inhibition of Rab27a expression increased viral multiplication and the intracellular levels of WNV structural proteins, E and prM proteins. Rab27a partially colocalized with E protein, mainly in the perinuclear region, while inhibition of Rab27a expression resulted in diffuse subcellular localization of E protein. In addition, some of the perinuclear E protein colocalized with the lysosomal marker LAMP1, and inhibition of lysosomal acidification increased intracellular levels of Rab27a and E proteins. These observations suggested that Rab27a inhibits WNV multiplication by inducing the degradation of viral protein in lysosomes.
  • Ubiquitin accumulation induced by the finger and palm sub-domains of NS5 modulates the replication of West Nile virus.
    Shintaro Kobayashi; Ryoko Kawakami; Chisaki Takeda; Keisuke Maezono; Passawat Thammahakin; Haruto Eguchi; Bernard M Hang'ombe; Yasuko Orba; Hirofumi Sawa; Kentaro Yoshii; Hiroaki Kariwa
    Virology, 588, 109902, 109902, Nov. 2023, [International Magazine]
    English, Scientific journal, West Nile virus (WNV) causes encephalitis in human and animals. WNV is phylogenetically classified into at least five distinct genetic lineages with different pathogenicity. The pathogenesis of West Nile encephalitis is affected by ubiquitin accumulation in infected cells, but the mechanism is unknown. In this study, the association between ubiquitin accumulation and WNV pathogenicity was investigated. Ubiquitin accumulation was detected in cells infected with NY99 strain belonging to lineage-1, but not FCG and Zmq16 strains belonging to lineage-2. Substitution of the Finger and Palm sub-domains of NS5 from lineage-1 to -2 decreased ubiquitin accumulation and viral replication. Furthermore, the survival rate was increased, and viral replication and ubiquitin accumulation in the brain were attenuated, in mice inoculated with the substituted WNV compared with lineage-1 WNV. Therefore, the intracellular ubiquitin accumulation induced by the Finger and Palm sub-domains of NS5 is linked to the differences in pathogenicity among WNV lineages.
  • Detection of disease-associated microglia among various microglia phenotypes induced by West Nile virus infection in mice.
    Passawat Thammahakin; Keisuke Maezono; Naoya Maekawa; Hiroaki Kariwa; Shintaro Kobayashi
    Journal of neurovirology, 29, 4, 367, 375, Aug. 2023, [International Magazine]
    English, Scientific journal, West Nile virus (WNV) has emerged as a significant cause of viral encephalitis in humans and horses. However, the pathogenesis of the West Nile encephalitis remains unclear. Microglia are activated by WNV infection, and the pathogenic involvement of their phenotypes is controversial. In this study, we examined the diversity of microglia phenotypes caused by WNV infection by assessing various microglia markers and identified disease-associated microglia in WNV-infected mouse brain tissue. Cells positive for general microglia markers such as Iba1, P2RY12, or TMEM119 were detected in the control and WNV-infected brain tissue. The morphology of the positive cells in brain tissue infected by WNV was different from that of control brain tissue, indicating that WNV infection induced activation of microglia. The activated microglia were classified into various phenotypes by investigation of specific marker expression. Among the activated microglia, disease-associated microglia that were positive for CD11c and weakly positive for TMEM119 were detected close to the WNV-infected cells. These results indicate that WNV infection induces activation of diverse microglia phenotypes and that disease-associated microglia may be associated with the pathogenicity of WNV infection in the mouse brain.
  • Development of recombinant West Nile virus expressing mCherry reporter protein.
    Shintaro Kobayashi; Yukine Fukuda; Kentaro Yoshii; Passawat Thammahakin; Keisuke Maezono; Luděk Eyer; Daniel Růžek; Hiroaki Kariwa
    Journal of virological methods, 317, 114744, 114744, Jul. 2023, [International Magazine]
    English, Scientific journal, West Nile virus (WNV) is transmitted to humans and animals by a mosquito and enters the central nervous system, leading to lethal encephalitis. Reporter viruses expressing fluorescent proteins enable detection of infected cells in vitro and in vivo, facilitating evaluation of the dynamics of viral infection, and the development of diagnostic or therapeutic methods. In this study, we developed a method for production of a recombinant replication-competent WNV expressing mCherry fluorescent protein. The expression of mCherry was observed in viral antigen-positive cells in vitro and in vivo, but the growth of the reporter WNV was reduced as compared to the parental WNV. The expression of mCherry was stable during 5 passages in reporter WNV-infected culture cells. Neurological symptoms were observed in mice inoculated intracranially with the reporter WNV. The reporter WNV expressing mCherry will facilitate research into WNV replication in mouse brains.
  • Development of a highly specific serodiagnostic ELISA for West Nile virus infection using subviral particles.
    Keisuke Maezono; Shintaro Kobayashi; Koshiro Tabata; Kentaro Yoshii; Hiroaki Kariwa
    Scientific reports, 11, 1, 9213, 9213, 28 Apr. 2021, [International Magazine]
    English, Scientific journal, West Nile virus (WNV), a member of the Japanese encephalitis virus (JEV) serocomplex group, causes lethal encephalitis in humans and horses. Because serodiagnosis of WNV and JEV is hampered by cross-reactivity, the development of a simple, secure, and WNV-specific serodiagnostic system is required. The coexpression of prM protein and E protein leads to the secretion of subviral particles (SPs). Deletion of the C-terminal region of E protein is reported to affect the production of SPs by some flaviviruses. However, the influence of such a deletion on the properties and antigenicity of WNV E protein is unclear. We analyzed the properties of full-length E protein and E proteins lacking the C-terminal region as novel serodiagnostics for WNV infection. Deletion of the C-terminal region of E protein suppressed the formation of SPs but did not affect the production of E protein. The sensitivity of an enzyme-linked immunosorbent assay (ELISA) using the full-length E protein was higher than that using the truncated E proteins. Furthermore, in the ELISA using full-length E protein, there was little cross-reactivity with anti-JEV antibodies, and the sensitivity was similar to that of the neutralization test.
■ Other Activities and Achievements
■ Research Themes