1545: Increased Neutrophil Activation in Patients with Polymyalgia Rheumatica

Despina Michailidou¹, Linda Johansson², Runa Kuley¹, TING WANG¹, Payton Hermanson¹, Solbritt Rantapää-Dahlqvist² and Christian Lood¹, ¹Division of Rheumatology, University of Washington, Seattle, WA, ²Department of Public Health and Clinical Medicine, Rheumatology, Umeå University, Umeå, Sweden

Background/Purpose: Neutrophils are important in host defense. However, neutrophil activation has also been involved in the immunopathogenesis of several autoimmune diseases due to their many cytotoxic and inflammatory effector mechanisms. The purpose of this study was to assess whether neutrophil activation occurs in polymyalgia rheumatica (PMR) by evaluating circulating levels of calprotectin and neutrophil extracellular traps (NETs).

Methods: Levels of calprotectin and NETs, as assessed by myeloperoxidase (MPO)-DNA complexes, were measured in the plasma of healthy individuals (n=30) and patients with PMR (n=60) using ELISA. PMR patients were enrolled at time-point of active disease, as well as following glucocorticoid therapy (Table 1).

Results: Levels of calprotectin and NETs were elevated in patients with PMR as compared to healthy subjects (Table 2). The neutrophil activation marker, calprotectin, significantly decreased after corticosteroid therapy (p< 0.001) (Table 3), and was higher in patients with active PMR without overlapping GCA compared to patients with overlapping disease (p=0.014). Interestingly, musculoskeletal involvement as defined by pain and stiffness in shoulder and pelvic girdles was associated with elevated levels of calprotectin (p=0.036) before initiation of corticosteroid therapy.

Conclusion: Neutrophil activation occurs in patients with PMR and was associated with musculoskeletal involvement. Plasma calprotectin could be a reliable biomarker of treatment response in patients with PMR. However, NETs are not a sensitive predictive biomarker for reduction of systemic inflammation in PMR.
Table 1. Baseline demographic characteristics of patients with PMR

Table 2. Mean concentration of neutrophil markers, in patients with active PMR before corticosteroid therapy compared to healthy controls

Table 3. Mean concentration of neutrophil markers, blood cell counts, and acute phase reactants before and after glucocorticoid treatment in patients with PMR.
Disclosures: D. Michailidou, Chemocentryx, Pfizer US Pharmaceuticals Group; L. Johansson, None; R. Kuley, None; T. WANG, None; P. Hermanson, None; S. Rantapää-Dahlqvist, None; C. Lood, Eli Lilly, Gilead Sciences, Pfizer, Bristol-Myers Squibb(BMS), Redd Pharma, Horizon Diagnostic, Exagen Diagnostic.