OP0213 Ly6G+CXCR2-CD101- GRANULOCYTES REGULATE INFLAMMATION IN AXIAL SPONDYLOARTHRITIS

Background: TNFα and IL-23/IL-17 axis plays a pivotal role in the pathogenesis of axial spondyloarthritis (axSpA). Although inhibition of TNFα or IL-17 is a common treatment approach, long-term disease control is still often limited with these drugs. Reactivation of inflammation (clinical relapse) is frequently observed, and so far there is no definitive cure for axSpA using these treatments. Alternatively, the active stimulation of resolution of inflammation via activation of cytotoxic T-lymphocyte-associated Protein 4 (CTLA4) is a common treatment approach in e.g. rheumatoid arthritis. However, mechanisms that induce resolution of inflammation in axSpA are poorly understood. Recently, the heterogeneity of myeloid cells during the course of axSpA has been identified. While the immunoregulatory capacity of myeloid cells is well known from cancer and autoimmune diseases, their emergence, mechanisms of action, and therapeutic potential in axSpA remain unknown. Objectives: To investigate the role of regulatory myeloid cells in subsets of patients with radiographic axSpA. Methods: Axial inflammation was induced in Tg197 hTNFtg mice after hydrodynamic tail vein injection of IL-23 minicircle-DNA. CD11b+Ly6G+CXCR2-CD101- and CXCR2+CD101+ cells were flow-sorted and tested for suppressive function in T cell proliferation assays. Subsequently, results from mice were translated into humans. Peripheral blood was collected from 54 axSpA patients (ASDAS 2.02 ± 1.16) and 21 healthy controls. The abundance of CD66b+CXCR2-CD101-cells in the peripheral blood of active (n = 33) and inactive (n = 18; in inactive disease status according to ASDAS) axSpA patients and healthy controls was measured by flow cytometry. Biopsies from sacroiliac and facet joints of the lumbal spine were obtained from other 18 axSpA patients (BASDAI 5.2±1.4) and 8 non-inflammatory controls. The biopsies were taken under MRI (sacroiliac) or radiographic control (facet jonts) and immediately processed for imaging mass cytometry (IMC). IMC was performed with 37 validated antibodies for immunoprofiling as well as detecting resident mesenchymal cells. Results: IL-23 minicircle overexpression in 8 weeks old hTNFtg mice induced axial inflammation. Flow cytometric analyses of axial joints identified two main subtypes of neutrophils. While CXCR2+CD101+ neutrophils stimulated T cell proliferation,, sorted CXCR2-CD101- granulocytes from inflamed ankle joints exhibited potent immunosuppressive function in ex vivo T cell proliferation assays. Absolute numbers of CXCR2+CD101+ granulocytes increased after IL-23 overexpression, accompanied by a decrease in the CXCR2-CD101- to CXCR2+CD101+ ratio, indicating a local shift towards pro-inflammatory granulocytes. In r-axSpA patients, total neutrophil numbers, as well as CXCR2+CD101+ granulocytes, were significantly increased compared to healthy controls, independent of disease activity. In contrast, patients in clinical remission (as assessed by ASDAS) showed an increase of circulating CXCR2-CD101- granulocytes. To investigate the role of CXCR2-CD101- granulocytes at sites of inflammation in axSpA patients, we performed MRI guided biopsies of sacroiliac and facet joints of the lumbal spine. Immunoprofiling via IMC revealed a complex microenvironment of innate (innate lymphoid cells (ILCs), granulocytes) and adaptive immune cells (B and T cells) embeded in a mesenchymal network of fibroblasts and endothelial cells. Herein, CXCR2-CD101- immunoregulatory granulocytes particularly colocalized with pro-resolving ILC2s, suggesting their immuno-regulatory capacity. Conclusion: Our study established the existence of immunoregulatory CXCR2-CD101- granulocytes in axSpA. Their ability to inhibit T cell proliferation in vitro, along with their colocalization with pro-resolving immune cells at inflamed joints of axSpA patients, underscores their relevance in the pathophysiology of axSpA. Moreover, the negative correlation with disease activity suggests their potential as biomarkers and therapeutic targets in future treatment strategies. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: None declared.