Cellular and molecular mechanisms underlying the antinuclear autoimmune response in ANA+ juvenile idiopathic arthritis

• Applicant: Privatdozent Dr. Henner Morbach
• Subject Area: Pediatric and Adolescent Medicine
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446925698

Juvenile idiopathic arthritis (JIA) comprises a heterogeneous group of chronic inflammatory joint diseases in childhood. Current classification systems rely on clinical features and insufficiently reflect the underlying molecular endotypes. A subset defined by the presence of antinuclear antibodies (ANA⁺) is characterized by early disease onset, female predominance, and an increased risk of uveitis. Whether this phenotype represents a distinct molecular endotype remains unclear. In the previous funding period, we identified a marked expansion of peripheral helper T (Tph) cells in the synovial fluid of ANA⁺ JIA patients. These Tph cells induced by secretion of a “B helper” cytokine program the differentiation of plasma cells and double-negative B cells in vitro. In silico analyses and in vitro CRISPR-Cas9 knockout experiments using Tph cell differentiation assays revealed the transcription factor BHLHE40 as a key regulator of the Tph-associated cytokine program. scRNA-Seq data from synovial B cells suggest local affinity maturation of autoreactive B cell receptors (BCRs) with antinuclear specificity. The proposed project aims to elucidate the molecular mechanisms underlying local autoimmunity in ANA⁺ JIA. Building on single-cell RNA sequencing datasets generated in the previous funding period, we will analyze the polarization states, transcriptional programs, and functional modules of Tph cells. Additional key transcription factors will be identified by in silico gene perturbation and functionally validated in vitro through targeted gene editing. In parallel, we will perform paratyping of the synovial BCR repertoire to identify disease-specific BCR motifs, which will serve as templates for generating recombinant monoclonal antibodies to define potential autoantigen targets using proteomic analysis. In addition, clonal differentiation trajectories of antinuclear B cells within the synovial tissue will be reconstructed and the emergence of autoreactivity along these trajectories will be correlated with transcriptional programs. In the long term, this project is expected to contribute to a molecular reclassification of JIA and to inform the development of novel diagnostic and therapeutic strategies.

• DFG Programme: Research Grants