Association between levels of synovial anti‐citrullinated peptide antibodies and neutrophil response in patients with rheumatoid arthritis

Abstract

Rheumatoid arthritis (RA) is characterized by the presence of anti-citrullinated peptide antibodies (ACPAs) and neutrophils infiltrating the synovial fluid (SF) of the affected joints. The aim of this work was to analyze whether the presence of ACPAs in SF is associated with neutrophil infiltration and with their phenotype in the inflamed joints of RA patients. We found that in the presence of ACPAs, the number of synovial neutrophils correlated with severe disease activity. The SF were divided according to synovial ACPA levels in negative- (<25 U/mL), low- (25-200 U/mL) and high level (˃200 U/mL; ACPA ). We observed that IL-6, IL-17, and IL-8 were significantly elevated in ACPA SF and that IL-8 levels correlated positively with neutrophil counts and with worse clinical manifestations. Additionally, in vitro incubation of neutrophils with ACPA SF resulted in an increased ROS production and extracellular DNA release compared to neutrophils incubated with ACPA-negative SF. These exacerbated effector functions were associated with a fraction of ICAM-1-positive neutrophils, which were induced by ACPA SF. Likewise, in in vivo, we could also detect this subset among neutrophils present in ACPA SF. In conclusion, the data presented here shed light on the role of SF-ACPAs as inductors of a proinflammatory profile in neutrophils.

Rheumatoid Arthritis Synovial Fluid Neutrophils Drive Inflammation Through Production of Chemokines, Reactive Oxygen Species, and Neutrophil Extracellular Traps

“…One limitation of our study is the use of an in vitro model of RA to validate our transcriptomics data. Whilst the incubation of healthy control neutrophils in RA SF is a widely used model of the disease (48,(70)(71)(72), future studies should focus on validating the RA SF neutrophil phenotype using ex vivo RA SF neutrophils. There have been a number of reports on the properties of RA SF neutrophils and in general these show an activated phenotype, in terms of surface receptor expression, ROS production and apoptosis (see Introduction).…”

Neutrophil trafficking to lymphoid tissues: physiological and pathological implications

“…In recent years, the homogeneity of neutrophil population has become increasingly questionable, with detection of neutrophils exhibiting distinct functions and profiles leading to the concept of different subsets . Several studies have indeed demonstrated that alternatively activated and/or HEV‐recruited neutrophils can regulate the adaptive immune response by inhibiting B and T lymphocyte responses, in particular in the context of antibody production during vaccination challenge and infections . Whilst the mechanisms associated with such functions are not fully understood, neutrophil suppressive properties on T lymphocyte activities involve the release of reactive oxygen species, NO or Arginase 1 (Arg‐1) in close vicinity of targeted lymphocytes .…”

Neutrophil Function in an Inflammatory Milieu of Rheumatoid Arthritis

“…Solid evidence exists that supports the important role of NETs in the pathogenesis of RA [8, 9, 13, 20, 73]. NET formation has been identified as a link between the innate and adaptive immune responses in autoimmunity.…”

“…Sera and immunoglobulin fractions from RA patients with high levels of ACPA or RF significantly enhanced NETosis. In vitro incubation of neutrophils with ACPA high synovial fluid results in increased ROS production and extracellular DNA release compared to neutrophils incubated with ACPA-negative synovial fluid [20].…”