Background Recent animal studies have suggested that γδT-cells accumulate at enthesis, secrete IL-17 and are responsible for driving the spondyoarthritis (SpA) phenotype resulting from IL-23 overexpression in mice (1, 2). In humans examination of the immunological profile of enthesis has been hampered by lack of tissue. Recently, we used a novel strategy to show that group 3 innate lymphoid cells are present at the human enthesis (3). Here we extend our methodology to examine the broader immunological profile of human enthesis and to determine if γδT-cells are also present.
Objectives To characterise γδT-cells at human enthesis and adjacent peri-entheseal bone
Methods Human etheseal soft tissue (EST) and peri-entheseal bone (PEB) was harvested from normal spinous process in patients undergoing elective spinal orthopaedic procedures. Interspinous EST was dissected from PEB and enzymatically digested, followed by isolation of mononuclear cells. Flow cytometry was then used to determine the proportion of B-cells (CD45+, CD19+) NK cells (CD45+, CD3-, CD56+) and T-cells (CD45+, CD3+). T-cells were then sub divided based on expression of CD4 (T-helper cells), CD8 (Cytotoxic T-cells) and TCRγδ (γδT-cells). All entheseal data was compared to age-matched peripheral blood from healthy controls.
Results Entheseal digests contained on average a lower proportion of T-cells compared to peripheral blood (p=0.018). However, the proportion of T-cells not expressing either CD4 or CD8 was greater in entheseal tissues (p=0.021), this population was largely composed of γδT-cells. As a proportion of T-cells γδT-cells were 6 fold more numerous in EST compared to peripheral blood (p=0.024), and PEB had 3 fold more. 37% of EST γδT-cells expressed CCR6 this compared to 26% and 34% in PEB and peripheral blood respectively.
Conclusions γδT-cells are present in normal human enthesis and γδT-cells constitute a greater proportion of the T-cell pool compared to peripheral blood, making it likely that they represent a tissue resident population. Additionally, we observed a very similar proportion γδT-cells that expressed CCR6, a functional marker for IL-17 production, as was observed in mice (2). This is the first description of γδT-cells at the human enthesis and offers tentative confirmation of findings in mouse models where these cells play a key role in SpA pathogenesis.
Sherlock JP, Joyce-Shaikh B, Turner SP, Chao CC, Sathe M, Grein J, et al. IL-23 induces spondyloarthropathy by acting on ROR-gammat+ CD3+CD4-CD8- entheseal resident T cells. Nat Med. 2012 Jul;18(7):1069–76. PubMed PMID: 22772566.
Reinhardt A, Yevsa T, Worbs T, Lienenklaus S, Sandrock I, Oberdörfer L, et al. IL-23-dependent γδT cells produce IL-17 and accumulate in enthesis, aortic valve, and ciliary body. Arthritis & Rheumatology. 2016.
Cuthbert R, Fragkakis E, Dunsmuir R, Millner P, El-Sherbiny Y, McGonagle D. AB0028 Innate Lymphoid Cells Are Present at Normal Human Enthesis Providing A Potential Mechanism for Spondyloarthropathy Pathogenesis. Annals of the Rheumatic Diseases. 2016;75(Suppl 2):906-.
Disclosure of Interest None declared
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