Deficiencies of Runx3 and tissue-resident CD4+ intestinal epithelial lymphocytes link intestinal dysbiosis and inflammation in mouse and human spondyloarthropathy
Authors: Bhuyan Zaied Ahmed , Maradana Muralidhara Rao , Rahman M. Arifur , Mehdi Ahmed , Bergot Anne-Sophie , Simone Davide , Hanson Aimee L , Nel Hendrik , Garrido-Mesa Jose , El-Kurdi Marya , Kenna Tony , Leo Paul , Rehaume Linda , Brown Matthew A , Ciccia Francesco , Thomas Ranjeny 
Published: July 2022

AbstractObjectiveDisturbances in immune regulation, intestinal microbial dysbiosis and intestinal inflammation characterize ankylosing spondylitis (AS), which is associated with RUNX3 loss-of-function variants. ZAP70W163C mutant (SKG) mice have reduced ZAP70 signaling, spondyloarthritis and ileitis. At intestinal epithelial interfaces, lamina propria Foxp3+ regulatory T cells (Treg) and intraepithelial CD4+CD8αα+TCRαβ+ lymphocytes (CD4-IEL) control inflammation. TGF-β and retinoic acid (RA)-producing dendritic cells are required for induction of Treg and for CD4-IEL differentiation from CD4+ conventional or Treg precursors, with upregulation of Runx3 and suppression of ThPOK. We investigated Treg, CD4-IEL, ZAP70 and Runx3 in SKG mice and AS patients.MethodsWe compared ileal Treg and CD4-IEL numbers and differentiation in BALB/c and SKG mice, and with ZAP70 inhibition, and related differentially-expressed genes in terminal ileum to ChIP-seq-identified Runx3-regulated genes. We compared proportions of CD4-IEL in ileum and CD4+8+ T cells in blood of AS patients and healthy controls.ResultsZAP70W163C or ZAP70 inhibition prevented intestinal CD4-IEL but not Foxp3+ Treg differentiation in context of TGF-β and RA in vitro and in vivo, resulting in Runx3 and ThPOK dysregulation. CD4-IEL frequency and expression of tissue resident memory T-cell and Runx3-regulated genes was reduced in SKG intestine. Multiple under-expressed genes were shared with risk SNPs identified in human spondyloarthropathies. CD4-IEL were decreased in AS intestine. Double-positive T cells were reduced and Treg increased in AS peripheral blood.ConclusionHigh-affinity TCR-ZAP70 signalling is required for Runx3-mediated intestinal CD4-IEL differentiation from Treg. Genetically-encoded relative immunodeficiency of T cells underpins poor intestinal barrier control in mouse and human spondyloarthropathy.What is already known about this subject?Ankylosing spondylitis (AS) is associated with RUNX3 loss-of-function variants.Capacity of the AS T cell receptor repertoire to expand in response to infectious antigens is reduced.Foxp3+ regulatory T cells (Treg) are increased in AS intestine.ZAP70W163C mutant (SKG) mice have reduced ZAP70 signaling, spondyloarthritis (SpA) and ileitis.Intestinal epithelial Foxp3+ Treg and CD4+CD8+ cytotoxic lymphocytes (CD4-IEL) control local inflammation. CD4-IEL differentiate from Treg, with upregulation of Runx3 and suppression of ThPOK transcription factors.What does this study add?High-affinity TCR-ZAP70 signalling is required for Runx3-mediated intestinal CD4-IEL differentiation from TregIntestinal CD4-IEL and circulating CD4+CD8+ T cells are reduced in AS while circulating Treg are increased. Impaired CD8 expression may be correctible by TNF inhibition in AS CD4+ T cells.Deficiencies of Runx3 and tissue-resident CD4-IEL link intestinal dysbiosis and inflammation in mouse and human SpA.How might this influence clinical practice or future developments?Genetically-encoded relative T immunodeficiency underpins poor intestinal barrier control in SpA