Role of Mincle in Immune Responses to Orientia tsutsugamushi infection

Scrub typhus is a major public health concern for more than one billion people living in or travelling to endemic countries. The causative agent of scrub typhus, Orientia tsutsugamushi, is an obligate intracellular bacterium transmitted via bite of the Leptotrombidium mite (chigger). O. tsutsugamushi replicates in endothelial cells and macrophages (MF) and initial symptoms of infection are nonspecific, including cough, headache, and malaise. The lung is a target organ during infection and if treatment is delayed mild disease can progress to lethal pulmonary, cardiac, and neurologic syndromes. However, little is known regarding immune recognition of the bacterium and transitional mechanisms from mild to severe disease. The first objective of this work defined the contribution of Mincle, a C-type lectin receptor (CLR), in innate immunity to O. tsutsugamushi. Following lethal infection in C57BL/6 mice, pulmonary differential expression analysis revealed Mincle (Clec4e) among the top 5 greatest up-regulated genes, accompanied with CLR signaling partners (FcRg), and type 1-skewing cytokines/chemokines. To validate a role of Mincle in scrub typhus, we exposed murine bone marrow-derived macrophages (MF) to live or inactivated O. tsutsugamushi. We found that while heat-killed bacteria stimulated transitory Mincle expression, live bacteria generated a sustained Mincle response. Notably, infection had limited impact on other tested CLRs or TLRs. Sustained proinflammatory gene expression in MF was also induced by live, but not inactivated, bacteria; infected Mincle-/- MF significantly reduced proinflammatory responses compared with WT cells. The second objective was to examine the contribution of multiple CLRs to inflammation via inhibiting the adaptor protein necessary for CLR signal transduction (Syk). Infected/Syk-inhibited MF displayed significant reductions in Mincle, Clec5a, and proinflammatory/type-1 transcripts when compared with infected-but-untreated cells. Notably, the abrogated inflammatory response observed in infected Syk-inhibited cells was more pronounced than that seen in Mincle-/- cells, implicating multiple CLRs in sensing the bacterium. Surprisingly, MF displayed Syk-dependent, antiviral-like responses during infection. Together, we show that CLRs play an important role in sensing O. tsutsugamushi and generating proinflammatory immune responses during infection. My work has shed light on novel aspects of the innate response to O. tsutsugamushi and uncovered potential drivers of inflammation during infection.

Name thesis:degree_name

Microbiology and Immunology (Doctoral)

Grantor

The University of Texas Medical Branch at Galveston

Year dc:date.issued

2024

Author dc:creator

• Fisher, James

• Biology, Microbiology
• Health Sciences, Immunology

Handle dc:identifier.uri

https://hdl.handle.net/2152.3/12668

OAI identifier oai:identifier

oai:utmb-ir.tdl.org:2152.3/12668