Toll-like receptors in innate immunity and inflammation: from fundamental biology to clinic insights
TL;DR
Toll-like receptors (TLRs) function as highly regulated, multi-layered information-processing hubs controlled by post-translational modifications, epigenetics, and metabolism, the dysregulation of which directly drives diseases like lupus and sepsis.
Problem / question
How the innate immune system uses Toll-like receptors to reliably detect diverse pathogens and tissue damage without triggering excessive, self-destructive inflammation or autoimmune responses.
Methods
The authors synthesized decades of molecular immunology research, analyzing structural biology, proteomics, and genetic studies to map the intrinsic regulatory networks (including post-translational modifications, epigenetics, and metabolic rewiring) and cross-pathway interactions of mammalian TLRs.
Key findings
TLR signaling centers on supramolecular organizing centers (SMOCs) like the myddosome, which acts as a central hub rather than a linear cascade. This signaling is tightly constrained by negative feedback loops, including alternative splicing (e.g., the inhibitory MyD88-S isoform) and metabolic shifts (e.g., lipid mediator class switching to pro-resolving oxylipins). Genetic variants in these pathways directly drive disease: the TLR7 F506S mutation causes systemic lupus erythematosus (SLE), while TLR4 D299G increases susceptibility to Gram-negative sepsis. Additionally, pathogens and mRNA vaccines exploit these pathways, using RNA modifications like pseudouridine to evade TLR7/8 detection.
Why it matters
Understanding the precise molecular brakes and accelerators of TLR signaling enables the rational design of targeted immunotherapies, mRNA vaccine adjuvants, and treatments for autoimmune diseases and severe infections.
Limitations
The authors note ongoing controversy over whether certain endogenous danger signals (DAMPs like HSPs and HMGB1) directly activate TLRs or if past results were confounded by bacterial endotoxin contamination, and highlight that the mechanisms of many inhibitory splice variants remain uncharted.
Takeaway
TLR signaling is not a simple on/off switch but a dynamic, heavily regulated network integrating metabolic, epigenetic, and environmental cues, making it a prime target for therapeutic intervention in immune disorders.