<i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages
<i>Orientia tsutsugamushi</i> 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 ini...
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MDPI AG
2022-12-01
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| Series: | Pathogens |
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| Online Access: | https://www.mdpi.com/2076-0817/12/1/53 |
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| author | James Fisher Casey Gonzales Zachary Chroust Yuejin Liang Lynn Soong |
| author_facet | James Fisher Casey Gonzales Zachary Chroust Yuejin Liang Lynn Soong |
| author_sort | James Fisher |
| collection | DOAJ |
| description | <i>Orientia tsutsugamushi</i> 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 <i>O. tsutsugamushi</i> 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 <i>O. tsutsugamushi</i> in the presence of selective Syk inhibitors and analyzed a panel of CLRs and proinflammatory markers via qRT-PCR. We found that Mincle/<i>Clec4a</i> and <i>Clec5a</i> 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 (<i>Il12p40</i>, <i>Tnf</i>, <i>Il27p28</i>, <i>Cxcl1</i>) during infection. Additionally, expression of innate immune cytosolic sensors (<i>Mx1</i> and <i>Oas1</i>-3) was highly induced in the brain of lethally infected mice. We established that <i>Mx1</i> and <i>Oas1</i> expression was reduced in Syk-inhibited MΦ, while <i>Oas2</i>, <i>Oas3</i>, and <i>MerTK</i> were not sensitive to Syk inhibition. This study reveals that Syk-dependent CLRs contribute to inflammatory responses against <i>O. tsutsugamushi</i>. 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. |
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| issn | 2076-0817 |
| language | English |
| last_indexed | 2024-03-09T11:30:22Z |
| publishDate | 2022-12-01 |
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| spelling | doaj.art-39e7565a9fd14666b989a52336c157ee2023-11-30T23:53:05ZengMDPI AGPathogens2076-08172022-12-011215310.3390/pathogens12010053<i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in MacrophagesJames Fisher0Casey Gonzales1Zachary Chroust2Yuejin Liang3Lynn Soong4Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX 77555-1070, USADepartment of Pathology, University of Texas Medical Branch, Galveston, TX 77555-1070, USASchool of Medicine, University of Texas Medical Branch, Galveston, TX 77555-1070, USADepartment of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX 77555-1070, USADepartment of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX 77555-1070, USA<i>Orientia tsutsugamushi</i> 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 <i>O. tsutsugamushi</i> 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 <i>O. tsutsugamushi</i> in the presence of selective Syk inhibitors and analyzed a panel of CLRs and proinflammatory markers via qRT-PCR. We found that Mincle/<i>Clec4a</i> and <i>Clec5a</i> 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 (<i>Il12p40</i>, <i>Tnf</i>, <i>Il27p28</i>, <i>Cxcl1</i>) during infection. Additionally, expression of innate immune cytosolic sensors (<i>Mx1</i> and <i>Oas1</i>-3) was highly induced in the brain of lethally infected mice. We established that <i>Mx1</i> and <i>Oas1</i> expression was reduced in Syk-inhibited MΦ, while <i>Oas2</i>, <i>Oas3</i>, and <i>MerTK</i> were not sensitive to Syk inhibition. This study reveals that Syk-dependent CLRs contribute to inflammatory responses against <i>O. tsutsugamushi</i>. 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.https://www.mdpi.com/2076-0817/12/1/53<i>Orientia</i>obligate intracellular bacteriainnate immunitypattern recognition receptorSykC-type lectin |
| spellingShingle | James Fisher Casey Gonzales Zachary Chroust Yuejin Liang Lynn Soong <i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages Pathogens <i>Orientia</i> obligate intracellular bacteria innate immunity pattern recognition receptor Syk C-type lectin |
| title | <i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages |
| title_full | <i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages |
| title_fullStr | <i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages |
| title_full_unstemmed | <i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages |
| title_short | <i>Orientia tsutsugamushi</i> Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages |
| title_sort | i orientia tsutsugamushi i infection stimulates syk dependent responses and innate cytosolic defenses in macrophages |
| topic | <i>Orientia</i> obligate intracellular bacteria innate immunity pattern recognition receptor Syk C-type lectin |
| url | https://www.mdpi.com/2076-0817/12/1/53 |
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