Orientia tsutsugamushi Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages

James Fisher, Casey Gonzales, Zachary Chroust, Yuejin Liang, Lynn Soong

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Orientia tsutsugamushi is an obligately intracellular bacterium and an etiological agent of scrub typhus. Human studies and animal models of scrub typhus have shown robust type 1-skewed proinflammatory responses during severe infection. Macrophages (MΦ) play a critical role in initiating such responses, yet mechanisms of innate recognition for O. tsutsugamushi remain unclear. In this study, we investigated whether Syk-dependent C-type lectin receptors (CLRs) contribute to innate immune recognition and the generation of proinflammatory responses. To validate the role of CLRs in scrub typhus, we infected murine bone marrow-derived MΦ with O. tsutsugamushi in the presence of selective Syk inhibitors and analyzed a panel of CLRs and proinflammatory markers via qRT-PCR. We found that Mincle/Clec4a and Clec5a transcription was significantly abrogated upon Syk inhibition at 6 h of infection. The effect of Syk inhibition on Mincle protein expression was validated via Western blot. Syk-inhibited MΦ had diminished expression of type 1 cytokines/chemokines (Il12p40, Tnf, Il27p28, Cxcl1) during infection. Additionally, expression of innate immune cytosolic sensors (Mx1 and Oas1-3) was highly induced in the brain of lethally infected mice. We established that Mx1 and Oas1 expression was reduced in Syk-inhibited MΦ, while Oas2, Oas3, and MerTK were not sensitive to Syk inhibition. This study reveals that Syk-dependent CLRs contribute to inflammatory responses against O. tsutsugamushi. It also provides the first evidence for Syk-dependent activation of intracellular defenses during infection, suggesting a role of pattern recognition receptor crosstalk in orchestrating macrophage-mediated responses to this poorly studied bacterium.

Original languageEnglish (US)
Article number53
Issue number1
StatePublished - Jan 2023


  • C-type lectin
  • Orientia
  • Syk
  • innate immunity
  • macrophage
  • obligate intracellular bacteria
  • pattern recognition receptor

ASJC Scopus subject areas

  • Immunology and Allergy
  • Molecular Biology
  • General Immunology and Microbiology
  • Microbiology (medical)
  • Infectious Diseases


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