OP0062 CYTOKINE PRODUCING B CELLS SKEW MACROPHAGES TOWARDS A PRO-INFLAMMATORY PHENOTYPE IN GIANT CELL ARTERITIS

Background: Giant cell arteritis (GCA) is the most frequent form of systemic vasculitis affecting the temporal artery (TA) and the aorta. Macrophages and T cells are well recognized players in the pathogenesis of GCA while B cells are often not taken into account. Recently, changes in the circulating B cell compartment were documented in GCA and B cells were found to organize into tertiary lymphoid organs at the site of vascular inflammation (TA and aorta).1,2 The exact role of B cells in GCA is still unknown as no disease-specific antibodies have been defined. However, beside their role in humoral immunity, B cells can also produce various cytokines. In GCA, peripheral B cells of treated GCA patients, showed an enhanced capacity to produce pro-inflammatory cytokine Interleukin (IL)63 which is nowadays an important target of treatment in GCA.4 We hypothesize that B cells help shape the inflammatory response in GCA by producing effector and regulatory cytokines. Objectives: We aimed to assess the cytokine profile of circulating and lesional B cells in GCA and studied the effects on macrophage skewing. Methods: To assess B cells with the capacity to produce cytokines, cryopreserved peripheral blood mononuclear cells of 11 untreated GCA patients and 15 age- and sex-matched healthy controls (HC) were cultured for 3 days in the presence of CpG-ODN 2006. During the last 5 hours phorbol myristate acetate and Calcium Ionophore were added. Thereafter, intracellular effector (IL6, TNFa, IFNy, LTb) and regulatory B cell-related cytokines (IL10) were measured with flow cytometry. To assess potential skewing of macrophages by B cell products, THP-1 cells were differentiated into macrophages and stimulated for 24 hours with supernatant from stimulated B cells (n=6). Expression of IL23, IL6, IL1b, TNFa, MMP9 and YKL40 was assessed on mRNA level with qPCR. To assess local cytokine production, TA (n=11) and aorta tissue samples (n=10) of histologically-proven GCA patients were stained to detect CD20, IL6, TNFa, IFNy, LTb, and IL10 expression. For comparison, 14 aorta tissues samples of patients with an atherosclerosis-related aortic aneurysm were included. Results: In vitro stimulated B cells from untreated GCA patients showed an enhanced percentage of IL6+ B cells (median (IQR); 44 (41-52)) and of IL6+TNFa+ B cells (12 (8-24)) compared to stimulated B cells from HC (IL6+: 28 (23-39), IL6+TNFa+: 6 (4-24)). In addition, soluble factors, secreted by GCA derived and stimulated B cells, skewed macrophages towards a pro-inflammatory phenotype with enhanced expression of IL23, IL6, IL1b, and TNFa. Furthermore, these macrophages also showed higher expression of the tissue remodelling factor MMP9 and the pro-angiogenic factor YKL40. At the site of vascular inflammation, B cells were detected in the regions with clear TNFa, IL6, IFNY, LTb and IL10 expression in both the TA and aorta of GCA patients. Conclusion: This study demonstrates that circulating B cells of patients with GCA have the capacity to express pro-inflammatory cytokines (IL6 and TNFa) which can influence other cellular players in GCA. Specifically, B cell secreted soluble factors were able to skew macrophages towards a pro-inflammatory phenotype. In addition, this study provides evidence for an active role of B cells in shaping the cytokine milieu at the site of inflammation thereby revealing the B cell as a new target of intervention in GCA. References: [1]Ciccia, F. et al. Ectopic expression of CXCL13, BAFF, April and LT-β is associated with artery tertiary lymphoid organs in giant cell arteritis. Ann. Rheum. Dis.76, 235–243 (2017) [2]Graver, JC. et al. Massive B cell Infiltration and Organization Into Artery Tertiary Lymphoid Organs in the Aorta of Large Vessel Giant Cell Arteritis. Front. Immunol.10, 83 (2019) [3]Van Der Geest, KSM. et al. Disturbed B cell homeostasis in newly diagnosed giant cell arteritis and polymyalgia rheumatica. Arthritis Rheumatol.66, 1927–1938 (2014) [4]Stone, JH. et al. Trial of tocilizumab in giant-cell arteritis. N. Engl. J. Med.377, 317–328 (2017) Disclosure of Interests: Jacoba Carolien Graver: None declared, William Febry Jiemy: None declared, Dania Altulea: None declared, Annemieke Boots Consultant of: Grunenthal, Peter Heeringa: None declared, Wayel Abdulahad: None declared, Elisabeth Brouwer Speakers bureau: Roche, fees paid to UMCG, Maria Sandovici: None declared