Structural modeling and functional characterization of a novel gain-of-function TLR8 variant causing severe inflammatory syndrome

2026/02/23 by Nikolaos T. Skenteris, Elisa Luttermann, Sanjana Nair +32 · 2 voices
Immunology and Microbiology · #Immune Response and Inflammation #Immunodeficiency and Autoimmune Disorders #T-cell and B-cell Immunology

paper · pdf · doi:10.1172/jci.insight.187422

openalex publication_date 2026/02/23 · openalex created_date 2026/02/24 · openalex updated_date 2026/07/31

Abstract

With the increasing use of genetic sequencing to investigate inborn errors of immunity, rare variants are frequently identified, yet their clinical relevance often remains uncertain. Establishing pathogenicity requires a multidisciplinary approach that integrates genetic, structural, functional, and clinical data. Here, we used such a strategy to investigate a previously unreported hemizygous missense variant - alanine (A) to threonine (T) at residue 518 - in Toll-like receptor 8 (TLR8), identified in 2 male siblings with recurrent infections and systemic inflammation, characterized by a proinflammatory immune signature and B cell dysregulation. Functional studies showed that the TLR8 A518T variant enhanced NF-κB activation and increased secretion of proinflammatory cytokines compared with WT TLR8 upon stimulation, consistent with a gain-of-function effect. Protein degradation and turnover assays revealed reduced abundance of the mutant TLR8 protein due to faster turnover and increased proteasomal degradation. Computational modeling predicted enhanced structural stabilization of the active TLR8 homodimer interface via additional water-mediated hydrogen bonds introduced by the A518T substitution. Together, these findings integrating structural modeling with functional assays identify a novel TLR8 ligand-specific gain-of-function mutation resulting in complex immunopathology in 2 siblings.

Citations

• Comparative Protein Modelling by Satisfaction of Spatial Restraints
• The mutational constraint spectrum quantified from variation in 141,456 humans
• Human Inborn Errors of Immunity: 2022 Update on the Classification from the International Union of Immunological Societies Expert Committee
• Accurate proteome-wide missense variant effect prediction with AlphaMissense
• UCSF ChimeraX: Tools for structure building and analysis
• AmberTools
• OpenMM 8: Molecular Dynamics Simulation with Machine Learning Potentials

Discussions

• Sequencing has aided in the discovery of mutations in inborn errors of immunity, but their clinical relevance is often unclear Altfeld & team @leibnizliv.bsky.social identify a TLR8 mutation causing [bsky, 1 points, 0 comments]
• Sequencing has aided in the discovery of mutations in inborn errors of immunity, but their clinical relevance is often unclear ASCI member Altfeld & team @leibnizliv.bsky.social identify a TLR8 mutat [bsky, 1 points, 0 comments]

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