NETs are a source of citrullinated autoantigens and stimulate inflammatory responses in rheumatoid arthritis

The early events leading to the development of rheumatoid arthritis (RA) remain unclear, but formation of autoantibodies to citrullinated protein antigens (ACPAs) is considered a key pathogenic event. Neutrophils isolated from patients with various autoimmune diseases display enhanced neutrophil extracellular trap (NET) formation, a phenomenon that exposes autoantigens in the context of immunostimulatory molecules. We investigated whether aberrant NETosis occurs in RA, determined its triggers, and examined its deleterious inflammatory consequences. Enhanced NETosis was observed in circulating and RA synovial fluid neutrophils compared to neutrophils from healthy controls and from patients with osteoarthritis (OA). Further, netting neutrophils infiltrated RA synovial tissue, rheumatoid nodules, and skin. NETosis correlated with ACPA presence and levels and with systemic inflammatory markers. RA sera and immunoglobulin fractions from RA patients with high levels of ACPA and/or rheumatoid factor significantly enhanced NETosis, and the NETs induced by these autoantibodies displayed distinct protein content. Indeed, during NETosis, neutrophils externalized the citrullinated autoantigens implicated in RA pathogenesis, and anti-citrullinated vimentin antibodies potently induced NET formation. Moreover, the inflammatory cytokines interleukin-17A (IL-17A) and tumor necrosis factor-α (TNF-α) induced NETosis in RA neutrophils. In turn, NETs significantly augmented inflammatory responses in RA and OA synovial fibroblasts, including induction of IL-6, IL-8, chemokines, and adhesion molecules. These observations implicate accelerated NETosis in RA pathogenesis, through externalization of citrullinated autoantigens and immunostimulatory molecules that may promote aberrant adaptive and innate immune responses in the joint and in the periphery, and perpetuate pathogenic mechanisms in this disease.

Neutrophil extracellular traps are a source of citrullinated autoantigens and stimulate inflammatory responses in rheumatoid arthritis (P4061)

The early events leading to the development of rheumatoid arthritis remain unclear but formation of autoantibodies to citrullinated antigens is considered a key pathogenic phenomenon. Neutrophils isolated from patients with various autoimmune diseases display enhanced extracellular trap formation, a phenomenon that externalizes autoantigens and immunostimulatory molecules. We investigated if aberrant NETosis occurs in RA, its triggers and deleterious inflammatory consequences. Enhanced NETosis was observed in circulating and synovial fluid RA neutrophils. NETosis correlated with ACPA levels and with systemic inflammatory markers. RA sera and immunoglobulin fractions from RA patients with high levels of ACPA and/or rheumatoid factor significantly enhanced NETosis, and the NETs induced by these autoantibodies displayed distinct protein content. During NETosis, neutrophils externalized citrullinated autoantigens implicated in RA pathogenesis, while anti-citrullinated vimentin antibodies potently induced NET formation. In turn, NETs significantly augmented inflammatory responses in RA and OA synovial fibroblasts, including induction of IL-6, IL-8, chemokines and adhesion molecules. These observations implicate accelerated NETosis in RA pathogenesis, through externalization of citrullinated autoantigens and immunostimulatory molecules that may promote aberrant immune responses in the joint and in the periphery and perpetuate pathogenic mechanisms in this disease.

Absorption and excretion of the hydrophobic surfactant, 14C-poloxalene 2930, in the rat

Absorption and excretion of 14C-Poloxalene 2930 (PX), a nonionic hydrophobic surfactant of large molecular weight, were studied using bile fistula rats. Approximately half of the dose infused intraduodenally was absorbed and some of the absorbed surfactant was excreted in bile. The remainder was excreted in urine. Only trace quantities of the 14C-PX were recovered in liver and carcass at termination of the study. Two studies were also performed with 14C-PX incorporated into the diet. In the first feeding study of 7 days duration, most of the agent was excreted via the gastrointestinal tract within 72 hr of discontinuing treatment. In the second study, rats were fed dietary 14C-PX for 7, 14, or 23 days to determine whether the surfactant continued to accumulate in the body as the test period was extended. Further accumulation did occur between the 7th and 14th days but not when feeding was continued for a total of 23 days. Of the amount of 14C-PX ingested after 23 days of feeding, essentially all was excreted by the end of 7 days after discontinuing treatment. These studies indicate that despite its large molecular weight of about 3,000 some 14C-PX is absorbed. Furthermore, absorbed material is promptly excreted in bile and urine with little retained in body tissues.