OP0029 NEUTROPHIL EXTRACELLULAR TRAPS IN GIANT CELL ARTERITIS INFLAMED TEMPORAL ARTERIES: LOCALIZATION, CO-EXPRESSION OF INFLAMMATORY CYTOKINES AND ASSOCIATION WITH DISEASE EXTENSION

Background:

Giant cell arteritis (GCA) represents the most prevalent form of systemic vasculitis in elderly, characterized by a remarkable heterogeneity in terms of clinical and histological phenotype, the pathogenetic mechanisms and treatment selection (1). An interplay between cells of both innate and adaptive immunity, appear to govern the pathophysiologic mechanisms (2). Among the different cellular populations, neutrophils may hold a central role in GCA pathogenesis, since they are present in abundance in tissue injury (3,4). Most importantly, they are a source of neutrophil extracellular traps (NETs) that may deliver immunocompetent substances, necessary for the perpetuation of the inflammatory response (5). The detection and function of NETs have not been studied in GCA.

Objectives:

To explore the presence and clinical significance of NETs in temporal artery biopsies (TABs) of patients with GCA.

Methods:

Ten patients with GCA [5 with limited cranial vasculitis (CV) and 5 with associated generalized large vessel vasculitis (LVV), as defined by 18F-fluorodeoxyglucose (FDG) positron-emission tomography with computed tomography (PET/CT)] and 8 patients with polymyalgia rheumatica (PMR) were studied. GCA and PMR patients fulfilled the 1990 ACR and 2012 EULAR/ACR provisional classification criteria, respectively. The presence, location, quantitation and decoration of NETs with IL-6, IL-1β, and IL-17A were assessed in TABs at the time of disease diagnosis by tissue immunofluorescence and confocal microscopy. Quantification of NETs in tissue sections was performed using the Imaris v.9.3 software that counts the total measure volume instead of only the projection area (6). Serum levels of IL-6 and IL-17A around the time of tissue biopsy were also evaluated in all patients.

Results:

All temporal artery biopsies from GCA patients had NETs located mainly in the adventitia, adjacent to the vasa vasorum, whereas TABs from PMR patients had no NET structures. LVV was associated with a higher NETs to total tissue volume ratio, compared to CV-GCA [p=0.0317]. NETs decorated with IL-6 were present in TABs of all LVV and 3 of 5 CV-GCA patients, while IL-17A positive NETs were observed in all GCA patients. IL-1β-positive NETs were not detected in any GCA patient. No relation was found between serum IL-6 and IL17A levels and NETs containing IL-6 and/or IL-17A.

Conclusion:

NETs bearing IL-6 and IL-17A cytokines are present in inflamed GCA-TABs. IL-6 positive NETs are associated with the LVV phenotype and might be useful as a tissue biomarker for disease severity and extent.

References:

[1]K. S. M. van der Geest et al. Arthritis Rheumatol, 2018;70:1366-76.

[2]C. Salvarani et al. Lancet, 2008;372:234-45.

[3]D. Chatelain et al. Ann Rheum Dis, 2009;68:84-8.

[4]S. Nadkarni et al. Circ Res, 2014;114:242-8.

[5]V. Mutua et al. Clin Rev Allergy Immunol, 2020.

[6]S. V. Costes et al. Biophys J, 2004;86:3993-4003.

Disclosure of Interests:

None declared

Leptin induces the expression of functional tissue factor in human neutrophils and peripheral blood mononuclear cells through JAK2-dependent mechanisms and TNFalpha involvement

INTRODUCTION

Leptin is an adipocyte-derived cytokine primarily involved in the regulation of body weight and energy balance. In vivo studies suggest that leptin promotes platelet aggregation and thrombosis. Neutrophils are involved in the crosstalk between inflammation and thrombosis in clinical disorders. Leptin is also involved in the regulation of inflammation.

AIM

We examined the in vitro effects of leptin on the expression of tissue factor (TF), the primary initiator of coagulation, in healthy neutrophils.

MATERIALS AND METHODS/RESULTS

The effects on TF expression were assayed functionally using a modified prothrombin time (mPT), as well as at mRNA and protein levels. The same experiments were performed in parallel with PBMC. Leptin induced functional TF and increased TF mRNA and protein expression in both cell types, as determined by mPT, real-time RT-PCR, western blot, flow cytometry, immunocytochemistry. Inhibition studies revealed that the effect of leptin on TF expression is mediated, at least in part, by JAK2 and PI3K. Our findings, after neutralising TNFalpha in supernatants of leptin-treated cells, also suggest the involvement of TNFalpha in the leptin-induced TF expression in leukocytes.

CONCLUSIONS

This study indicates a novel link between inflammation, obesity and thrombosis by showing that leptin is able to trigger the extrinsic coagulation cascade. This work suggests a possible mechanism of the thrombotic effects of hyperleptinemic-associated clinical disorders.

MEFV alterations and population genetics analysis in a large cohort of Greek patients with familial Mediterranean fever

Familial Mediterranean fever (FMF) is a disease characterized by recurrent, self-limiting bouts of fever and serositis and caused by altered pyrin due to mutated MEFV gene. FMF is common in the Mediterranean Basin populations, although with varying genetic patterns. The spectrum and clinical significance of MEFV alterations in Greece has yet not been elucidated. The aim of this study was to analyze the spectrum of MEFV alterations in FMF patients and healthy individuals in Greece. A cohort of 152 Greek FMF patients along with 140 Greek healthy controls was enrolled. Non-isotopic RNase cleavage assay (NIRCA) and sequencing allowed mutational and haplotypic analysis of the entire coding sequence of MEFV. The ARLEQUIN 2.0, DNASP 4.0 and PHYLIP software were used for population genetics analysis. Among patients, 127 (83.6%) carried at least one known mutation. The most common mutations identified were M694V (38.1%), M680I (19.7%), V726A (12.2%), E148Q (10.9%) and E230K (6.1%). The total carrier rate among healthy individuals was 0.7%. The presence of R202Q homozygosity in 12 of the remaining 25 MEFV negative FMF patients might be considered as disease related in Greeks. Population genetics analysis revealed that Greeks rely closer to the eastern rather than western populations of the Mediterranean Basin.