Background/Purpose: In spondyloarthropathy (SpA), arthritis is often associated with gut inflammation. The strong genetic association with HLA-B27 implicates involvement of T cells, but how gut dysbiosis, T cells and SpA are mechanistically linked remain unknown. In the SpA-susceptible ZAP-70W163C SKG mice, Gram-negative dysbiosis is associated with disease severity following curdlan injection. They exhibit defective thymic selection and impaired T cell tolerance, including dysfunctional Tregs, aberrant CD4+CD8+ intraepithelial cytotoxic T lymphocytes, and impaired control of mouse mammary tumour virus (MMTV) superantigen responses. In this study, we investigated the T cell response mediating ileitis and arthritis to gut pathobiont Parabacteroides goldsteinii (Pg; a species of Bacteroidaceae enriched in the SKG stool post-curdlan) and its role in mediating ileitis and arthritis in SKG and BALB/c mice.

Methods: Germ-free (GF) SKG and BALB/c mice were orally mono-associated with Pg or remained GF for 4 weeks prior to i.p. curdlan injection. CD4+ and CD8+ T cells were FACS-sorted from mesenteric (MLN), popliteal lymph nodes (PLN) at day 6 post curdlan and from ankle joints at day 35 post curdlan. The transcriptome, TCR clonality and usage were analysed by paired scRNA/TCR sequencing combined with CITE-seq using the 10x Genomics pipeline. Bioinformatics analysis was performed using ScanPy, Dandelion, Scirpy pipelines and IEDB database.

Results: At 5 weeks post-curdlan, Pg-SKG mice developed ileitis and SpA whilst Pg-BALB/c and GF animals were resistant. Naïve T cells, T follicular helper cells (Tfh), early activated T cells, resident-memory T cells (Trm), regulatory Trm cells (Treg-Trm), α4β7 integrin+ T cells were found in the CD4+ compartment, whilst many cell clusters in CD8+ T cells expressed exhaustion-related genes, such as Hspa1a, Tox, Lag3 and Ctla4. Notably, many α4β7 integrin+ effector T cells were found in Pg-SKG ankle and PLN suggestive of their gut origins. Also, IL-17-producing Trm and Treg-Trm cells were enriched in the arthritic ankle joints of Pg-SKG mice and exhibited the highest clonality within the CD4+ compartment. These IL-17+ subsets preferentially used TRBV31, TRBV20, and TRBV12-2, of which TRBV12-2 is known to recognize MMTV superantigens. A conserved TCR motif consisted of 14 amino acids was observed across the expanded clones. Structural prediction for this TCR using IEDB database implicated microbial and host-derived proteins, including GPER protein, inner membrane protein YeiH, small nuclear ribonucleoprotein Prp3, and type II secretion system protein GspD in Chlamydia trachomatis, as potential reactive antigens.

Conclusion: Gut-derived Pg drives ileitis and arthritis in SpA-prone SKG mice by promoting an IL-17+ tissue-resident memory T cell response in the joints. These pathogenic helper T cells may arise from conventional or regulatory T cells in the gut responding to bacterial or viral superantigens in the ankle, providing insight into how gut pathobionts can trigger SpA. Targeting specific TCR motifs, IL-17+ Trm, or their microbial/viral triggers may offer new revenues for treating gut-joint axis inflammation in an antigen-specific manner.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/enrichment-of-putative-bacteria-reactive-gut-derived-il-17-tissue-resident-memory-helper-t-cells-in-arthritic-ankles-in-the-skg-mouse-model-of-spondyloarthritis/