Treatment of Autoimmune Inflammation by a TLR7 Ligand Regulating the Innate Immune System

Tomoko Hayashi,Linda Vuong,Christine Gray,Fitzgerald Lao,Dennis A Carson,Michael Chan,Brian Crain,Rommel I Tawatao,Howard B Cottam,Maripat Corr,Shiyin Yao,Laurel L Lenz

doi:10.1371/journal.pone.0045860

Abstract

The Toll-like receptors (TLR) have been advocated as attractive therapeutic targets because TLR signaling plays dual roles in initiating adaptive immune responses and perpetuating inflammation. Paradoxically, repeated stimulation of bone marrow mononuclear cells with a synthetic TLR7 ligand 9-benzyl-8-hydroxy-2-(2-methoxyethoxy) adenine (called 1V136) leads to subsequent TLR hyporesponsiveness. Further studies on the mechanism of action of this pharmacologic agent demonstrated that the TLR7 ligand treatment depressed dendritic cell activation, but did not directly affect T cell function. To verify this mechanism, we utilized experimental allergic encephalitis (EAE) as an in vivo T cell dependent autoimmune model. Drug treated SJL/J mice immunized with proteolipid protein (PLP)139–151 peptide had attenuated disease severity, reduced accumulation of mononuclear cells in the central nervous system (CNS), and limited demyelination, without any apparent systemic toxicity. Splenic T cells from treated mice produced less cytokines upon antigenic rechallenge. In the spinal cords of 1V136-treated EAE mice, the expression of chemoattractants was also reduced, suggesting innate immune cell hyposensitization in the CNS. Indeed, systemic 1V136 did penetrate the CNS. These experiments indicated that repeated doses of a TLR7 ligand may desensitize dendritic cells in lymphoid organs, leading to diminished T cell responses. This treatment strategy might be a new modality to treat T cell mediated autoimmune diseases.

Highlights

The innate immune system forms part of the first line defense of barrier tissues and immuno-privileged sites
Tlr72/2 and wild type (WT) T cells the drug did not directly affect T cells. We extended these studies to the experimental allergic encephalitis (EAE) model where SJL/J mice immunized with peptide from myelin proteolipid protein (PLP)139–151 [10] were treated with daily doses of 1V136 or vehicle after the antigen priming phase beginning on day 6
Responses As EAE is a T cell driven disease, we examined if treatment with an innate immune stimulating agent (1V136) could influence an antigen specific T helper (Th) cell response after the initial priming phase

Summary

Introduction

The innate immune system forms part of the first line defense of barrier tissues and immuno-privileged sites. The discovery that synthetic molecules can bind specific TLRs has generated interest for the development of novel therapeutics for diseases that involve innate immunity. TLR7 recognizes naturally occurring single strand (ss) RNA and synthetic low molecular weight ligands, including imidazoquinolines, and purine-like molecules [2,3,4]. Among the latter, 9-benzyl-8-hydroxy-2-(2-methoxyethoxy) adenine (SM360320; designated here as 1V136), has been shown to be a potent and specific TLR7 agonist [5]. The concomitant pharmacological down-regulation of the MyD88 signaling pathway was neuroprotective in vivo and attenuated inflammatory responses in the myelin oligodendrocyte glycoprotein (MOG) peptide induced experimental allergic encephalitis (EAE) model of multiple sclerosis (MS) [6]. The in vivo mechanism of action of the drug was not determined [6]

Methods

Results

Conclusion