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

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.

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Publication Details

Journal
JCI Insight
Published
2026-02-23
DOI
https://doi.org/10.1172/jci.insight.187422
Primary Topic
Immune Response and Inflammation
Type
article
Field-Weighted Citation Impact
0.00

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article

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

Altfeld Marcus, Christian Schlein, Brigitte Beifuss, Jana Hennesen et al.
JCI Insight
Immune Response and Inflammation
article

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

Altfeld Marcus, Christian Schlein, Brigitte Beifuss, Jana Hennesen, Felix R. Stahl, Maria Pujantell, Felix J. Flomm, Veit Hornung, Marie Eggers, Michael Kutsche, Benedetta Padoan, Marleen Bérouti, Heike Hildebrandt, F. Koch-Nolte, Ioannis Evangelakos, Urte Matschl, Nicola M. Tomas, Fabian Hausmann, Viacheslav O. Nikolaev, Sanjana Nair, I. Kötter, Benjamin Grünhagel, Janna Marieke Claussen, Eva Tolosa, Marc Lütgehetmann, Maya Topf, Christian Kubisch, Saskia Biskup, Patrick Blümke, Elisa Luttermann, Nikolaos T. Skenteris, Anika Salfelder, Katrin Rading, Silke Giesemann-Jansen, Madeleine J. Bunders
article en

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.

JCI InsightVol. 11(4)
Leibniz Institute of Virology (LIV) (DE), Universität Hamburg (DE), Instituto de Salud Carlos III (ES), German Center for Pediatric and Adolescent Rheumatology (DE), University Medical Center Hamburg-Eppendorf (DE), Praxis für Humangenetik Tübingen (DE), HNO Bad Bramstedt (DE), German Centre for Cardiovascular Research (DE), Institute of Immunology (HR), Centre for Structural Systems Biology (DE), Institute of Virology of the Slovak Academy of Sciences (SK), Ludwig-Maximilians-Universität München (DE)
Leibniz-Gemeinschaft
Good health and well-being
Openalex Percentile: Top 45%
Immune Response and Inflammation
DOIOpen Access PDFOpenAlex
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