Background/Purpose: In ankylosing spondylitis, spondyloarthritis (SpA) is often associated with gut inflammation. The strong genetic association with HLA-B27 and expanded CD8 TCR public clonotypes implicate T cells in the pathogenesis, but it remains unclear how gut dysbiosis, T cells and SpA are mechanistically linked. ZAP70W163C SKG mice have a relative CD4+ lymphopenia with enrichment of Foxp3+ Treg, and a Th17 skew compared to BALB/c mice and ileal CD4+CD8+ cytotoxic T cells are deficient. SKG mice develop IL-23-dependent SpA, ileitis and faecal dysbiosis enriched in Gram-negative pathobionts after systemic β-1,3-glucan (curdlan). Bacteroidaceae and Porohvromonadaceae are dominant families in SKG relative to BALB/c stool. This study compared T cell clonotypic expansion in gut and joint draining lymph nodes, spleen and ankle joint, and stool metabolomics in gnotobiotic Parabacteroides goldsteinii (Bacteroidaceae Pg) SpA-prone SKG mice and tolerant BALB/c mice.

Methods: Germ-free (GF) SKG or BALB/c mice were gavaged or not with Pg before i.p. curdlan. Mesenteric (MLN), popliteal (PLN), lumbar-aortic (LALN) lymph nodes and spleen were collected at 1 week; ankle were collected at 5 weeks post-curdlan then analyzed by flow cytometry. CD4+ and CD8+ T cells sorted from MLN, PLN and the ankles, along with myeloid cells sorted from the ankles were subjected to scRNA/TCR sequencing combined with CITE-seq. Stool samples collected at 5 weeks post-curdlan were investigated with untargeted metabolomics using LC-MS.

Results: Pg-SKG mice developed ileitis and SpA whilst Pg-BALB/c mice remained healthy 5 weeks post-curdlan. GF mice developed enthesitis only. In Pg-SKG mice, CD44+Ki67+ T cells were significantly more frequent among CD8+ T cels and CD4+ conventional and regulatory T cells in MLN, PLN and ankle than in Pg-BALB/c mice (p< 0.05). Paired scRNA/TCR-seq in Pg-SKG ankle identified the most expanded CD4+ clonotypes as IL-17+ resident memory (Trm), Treg, IL-17+ Treg, and IL-17+ γδ T cells. The most expanded CD8+ clonotypes were Tfh-like CD4+CD8+, CXCR3+ and naïve T cells. IL-17+ CD4 Trm and IL-17+ Treg shared TCR clonotypes. Myeloid cells in SKG ankle were enriched in type 1 interferon-stimulated genes. Stool LC-MS yielded 1310 putative metabolites. Metabolites with anti-inflammatory/microbial properties were over-expressed in Pg-BALB/c stool, including the immunosuppressive molecule myriocin/FTY700.

Conclusion: These data indicate that Pg acts as a commensal in BALB/c mice but pathobiont in SKG mice, associated with downregulation of its immune regulatory properties. Pathogenic self or bacteria-reactive Th17 expand from conventional and regulatory T cells in SKG mice in the context of type 1 interferon-driven inflammatory myeloid antigen-presenting cells.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/self-or-bacteria-reactive-th17-expand-from-conventional-and-regulatory-t-cells-in-parabacteroides-goldsteinii-gnotobiotic-arthritic-skg-mice-in-context-of-interferon-driven-synovial-inflammatory-mac/