Neutrophil extracellular traps regulate IL-1β-mediated inflammation in familial Mediterranean fever

Inflammatory attacks of familial Mediterranean fever (FMF) are characterised by circulation and influx of high number of polymorphonuclear neutrophils (PMN) in the affected sites and profound therapeutic effect of IL-1β inhibitors. We investigated the role of neutrophil extracellular traps (NET) in the pathogenesis of FMF, and their involvement in IL-1β production.

Blood samples were obtained from six FMF patients during remissions and from three patients during attacks. NET formation and NET components were studied by fluorescence techniques, immunobloting and MPO-DNA complex ELISA.

PMNs from patients released NETs decorated with IL-1β during disease attacks. On the other hand, PMNs from patients during remission were resistant to inflammatory stimuli that induce NET release in PMNs from control subjects. Lower basal autophagy levels were identified in PMNs during remission, while induction of autophagy facilitated NET release, suggesting that autophagy is involved in the regulation of NET release. During the resolution of attacks, inhibition of NET formation by negative feedback mechanism was also observed. The anti-inflammatory agents, colchicine and DNAse I, inhibited IL-1β production in PMNs and IL-1β activity in NETs, respectively.

We suggest two additive events for triggering the FMF attack; the production of IL-1β by PMNs and its release through NETs. At the same time NETs, homeostatically, downregulate further NETosis, facilitating the resolution of attack. Compensatorly, lower basal autophagy of PMNs may protect from crises by attenuating the release of pro-inflammatory NETs.