New Checkpoint in TLR7/8 Sensing Rewrites Innate Immune Rules

March 14, 2026 Members in the News, Special Article of Interest

A recent study by Alharbi et.al. from the Gantier Lab published in Nature Immunology, “2′-O-Methyl-guanosine RNA fragments antagonize TLR7 and TLR8 to limit autoimmunity”, showed that TLR7 and TLR8 sensing is kept in check by naturally occurring 2′-O-methyl (2′-OMe)-modified ribosomal RNA fragments, avoiding autoimmune responses to host RNA in the absence of pathogens. Their study focuses on the functional and structural characterization of the binding between 2′-OMe-Guanosine RNA fragments and TLR7/8 receptors. They discovered that this interaction takes place in a new site, apart from the already known binding sites (Site 1 and 2), which results in an inactive open conformation of the dimers. Furthermore, they described how some rare variants in TLR7 and TLR8 impacting this antagonist binding site lead to autoimmunity due to lack of TLR7 and/or TLR8 inhibition. Thus, they provided a new model for TRL7/8 sensing and opened the avenue for potential RNA-based therapeutics for TLR7/8-driven autoimmune pathologies.

ABSTRACT

Recognition of RNA fragments by Toll-like receptor 7 (TLR7) and TLR8 helps to initiate the innate immune response against pathogens. An outstanding question is why RNA fragments generated during clearance of apoptotic cells fail to activate TLR7 and TLR8 signaling. Here we show that select 2′-O-methyl (2′-OMe) guanosine RNA fragments, including those derived from host RNAs, function as potent TLR7 and TLR8 antagonists and reduce TLR7 sensing in vivo. Mechanistically, these fragments bind to an antagonistic site on these proteins via their 5′-end 2′-OMe guanosine. These findings indicate that host RNAs evade detection because abundant ribosomal 2′-OMe-modified fragments naturally antagonize TLR7 and TLR8. Crucially, rare TLR7 and TLR8 mutations at this antagonist binding site decrease inhibition by 2′-OMe guanosine RNA fragments, leading to autoimmunity in patients. Collectively, this work redefines TLR7 and TLR8 sensing by introducing 2′-OMe guanosine as a natural immune checkpoint for their activation.

GRAPHICAL SUMMARY

Graphical Summary
Endosomal nucleic acids from various origins (for example host or pathogens) are sequentially processed by endo and exonucleases including RNase T2/2/6 and PLD3/4, respectively. Partial fragments ( ~ 2-3 bases) and single unmodified guanosine bind to site 2 and site 1 of TLR7, respectively. Cooperative binding to site 1 and 2 leads to a closed conformation of the dimers, allowing for downstream signaling. On the other hand, binding of RNA fragments containing 2′-OMe guanosine residues or 2′-OMe guanosine single nucleosides, originating from abundant ribosomal RNA, bind to the antagonistic sites of TLR7 resulting in an inactive open conformation of the dimers.

Michael Gantier, PhD, is an Adjunct Professor at the Department of Molecular and Translational Science, Monash University (Australia), and Research Group Head of Nucleic Acids and Innate Immunity group at Hudson Institute of Medical Research. On the one hand, his research focuses in understanding how innate immune sensors misfire, with the goal of preventing autoimmunity; on the other hand, he works to develop a new class of anti-inflammatory molecules, known as RNA therapeutics, to blunt aberrant inflammation at its source in a wide range of diseases. Dr Gantier has been a member of the Cytokines Society for the past 20 years and he received the Milstein Young Investigator Award in 2010, at the 8th Joint Meeting of the International Society for Interferon and Cytokine Research and the International Cytokine Society annual conference held in Chicago, USA.

Photo of Gantier and Sapkota
Dr Michael Gantier (left) and Dr Sunil Sapkota (right), corresponding authors of the article recently published in Nature Immunology.

Signals+ editor Maialen Sebastian-delaCruz interviewed Gantier about the latest article from his lab.

What was the key question you addressed with this paper, and what led you to ask it?

Over the past decade, pioneering studies conducted by Toshiyuki Shimizu and Veit Hornung’s teams have revealed that TLR7/8 are detecting endosomal RNA degradation products, specifically short RNA (ranging from two to three base fragments) and nucleosides (uridine and guanosine). Given that their agonism relies on such short RNA moieties, the receptors are unable to discern between endogenous (self) and exogenous (non-self) RNA fragments. Consequently, this raises the question of how TLR7/8 circumvent aberrant activation in steady-states, which are addressing in our manuscript.

Could you tell us how the initial idea and/or observation led to the major discovery?

We had previously observed that synthetic oligonucleotides (oligos) containing DNA and 2’-O-Methyl bases were highly effective inhibitors of TLR7, through an unknown mechanism. Conversely, some of these oligos were capable of potentiating TLR8 sensing (Alharbi et al., NAR 2020). We hypothesized that these oligos were degraded within endosomes, and that some of their fragments could bind to either inhibit or potentiate TLR7/8 sensing. Upon testing truncation products from our oligos, we discovered that 3-base RNA fragments with 2’-O-Methyl guanosine modification could antagonize TLR7 and TLR8 sensing. This led us to discover how TLR7/8 are inhibited, at the structural level.

Which of your findings was the most unexpected and/or exciting to you?

The most exciting finding was when we realized that a few TLR7/8 residues underpinning interaction with 2′-O-Methyl guanosine fragments were mutated in rare patients with autoimmunity. This suggests that these mutations may be the underlying cause of autoimmune diseases in these patients by preventing the binding of antagonistic RNA fragments to TLR7/8. Given the rarity of these receptor mutations, they highlight an essential aspect of biology that is fundamental to maintaining homeostasis.

If people take away only three things from this paper, what do you want them to be?

In short:

  1. We found that TLR7/8 are antagonized by 2′-O-Methyl guanosine RNA fragments which can originate from ribosomal RNA.
  2. These fragments bind to a new site in TLR7/8 to inactivate the proteins.
  3. Mutations impacting this antagonist binding site lead to autoimmunity.

Why is this discovery of particular significance to the Cytokines community?

Over the past 2 decades, our field has largely operated under the assumption that innate immune nucleic acid sensors detect molecular patterns that are unique to pathogens (referred to pathogen associated molecular patterns or PAMPs), to initiate rapid immune responses. Collectively with previous works from other labs, including those from Toshiyuki Shimizu and Veit Hornung’s teams, this study provides a new model for TLR7/8 sensing: activation results from a competition of naturally inhibited state of the receptors, not the selective binding of a PAMP. This questions the concept of self and non-self discrimination of RNA based on features by TLR7/8: the receptors are equally activated by both self and non-self RNAs, provided fragments generated by endo and exonucleases can outcompete natural antagonism.

Citation of the article:
Alharbi, A.S., Sapkota, S., Zhang, Z. et al. 2′-O-Methyl-guanosine RNA fragments antagonize TLR7 and TLR8 to limit autoimmunity. Nat Immunol (2026). https://doi.org/10.1038/s41590-026-02429-2

Link (open access): https://www.nature.com/articles/s41590-026-02429-2

On 24th February, by Maialen Sebastian-delaCruz, PhD