Persistent Toll-like receptor 7 stimulation induces behavioral and molecular innate immune tolerance

Katherine A. Michaelis, Mason A. Norgard, Peter R. Levasseur, Brennan Olson, Kevin G. Burfeind, Abigail C. Buenafe, Xinxia Zhu, Sophia Jeng, Shannon McWeeney, Daniel Marks

Research output: Contribution to journalArticle

Abstract

Toll-like receptors 7 and 8 (TLR7 and TLR8) are endosomal pattern recognition receptors that detect a variety of single-stranded RNA species. While TLR7/8 agonists have robust therapeutic potential, clinical utility of these agents is limited by sickness responses associated with treatment induction. To understand the kinetics and mechanism of these responses, we characterized the acute and chronic effects of TLR7 stimulation. Single-cell RNA-sequencing studies, RNAscope, and radiolabeled in situ hybridization demonstrate that central nervous system gene expression of TLR7 is exclusive to microglia. In vitro studies demonstrate that microglia are highly sensitive to TLR7 stimulation, and respond in a dose-dependent manner to the imidazoquinoline R848. In vivo, both intraperitoneal (IP) and intracerebroventricular (ICV) R848 induce acute sickness responses including hypophagia, weight loss, and decreased voluntary locomotor activity, associated with increased CNS pro-inflammatory gene expression and changes to glial morphology. However, chronic daily IP R848 resulted in rapid tachyphylaxis of behavioral and molecular manifestations of illness. In microglial in vitro assays, pro-inflammatory transcriptional responses rapidly diminished in the context of repeated R848. In addition to TLR7 desensitization, we found that microglia become partially refractory to lipopolysaccharide (LPS) following R848 pretreatment, associated with induction of negative regulators A20 and Irak3. Similarly, mice pre-treated with R848 demonstrate reduced sickness responses, hypothalamic inflammation, and hepatic inflammation in response to LPS. These data combined demonstrate that TLR7 stimulation induces acute behavioral and molecular evidence of sickness responses. Following prolonged dosing, R848 induces a refractory state to both TLR7 and TLR4 activation, consistent with induced immune tolerance.

Original languageEnglish (US)
JournalBrain, Behavior, and Immunity
DOIs
StateAccepted/In press - Jan 1 2019

Fingerprint

resiquimod
Toll-Like Receptor 7
Immune Tolerance
Microglia
Lipopolysaccharides
Toll-Like Receptor 8
Inflammation
RNA Sequence Analysis
Tachyphylaxis
Pattern Recognition Receptors
Gene Expression
Locomotion
Neuroglia
In Situ Hybridization
Weight Loss
Central Nervous System
RNA

Keywords

  • Desensitization
  • Innate immunology
  • Microglia
  • Sickness response
  • Tachyphylaxis
  • Tolerance
  • Toll-like receptors

ASJC Scopus subject areas

  • Immunology
  • Endocrine and Autonomic Systems
  • Behavioral Neuroscience

Cite this

Persistent Toll-like receptor 7 stimulation induces behavioral and molecular innate immune tolerance. / Michaelis, Katherine A.; Norgard, Mason A.; Levasseur, Peter R.; Olson, Brennan; Burfeind, Kevin G.; Buenafe, Abigail C.; Zhu, Xinxia; Jeng, Sophia; McWeeney, Shannon; Marks, Daniel.

In: Brain, Behavior, and Immunity, 01.01.2019.

Research output: Contribution to journalArticle

Michaelis, Katherine A. ; Norgard, Mason A. ; Levasseur, Peter R. ; Olson, Brennan ; Burfeind, Kevin G. ; Buenafe, Abigail C. ; Zhu, Xinxia ; Jeng, Sophia ; McWeeney, Shannon ; Marks, Daniel. / Persistent Toll-like receptor 7 stimulation induces behavioral and molecular innate immune tolerance. In: Brain, Behavior, and Immunity. 2019.
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AU - Burfeind, Kevin G.

AU - Buenafe, Abigail C.

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