NADPH oxidase derived reactive oxygen species are involved in human neutrophil IL‐1β secretion but not in inflammasome activation

Abstract

Neutrophils are essential players in acute inflammatory responses. Upon stimulation, neutrophils activate NADPH oxidase, generating an array of reactive oxygen species (ROS).Interleukin-1 beta (IL-1β) is a major proinflammatory cytokine synthesized as a precursor that has to be proteolytically processed to become biologically active. The role of ROS in IL-1β processing is still controversial and has not been previously studied in neutrophils. We report here that IL-1β processing in human neutrophils is dependent on caspase-1 and on the serine proteases elastase and/or proteinase 3. NADPH oxidase deficient neutrophils activated caspase-1 and did not exhibit differences in NALP3 expression, indicating that ROS are neither required for inflammasome activation nor for its priming, as has been reported for macrophages. Strikingly, ROS exerted opposite effects on the processing and secretion of IL-1β; whereas ROS negatively controlled caspase-1 activity, as reported in mononuclear phagocytes, ROS were found to be necessary for the exportation of mature IL-1β out of the cell, a role never previously described. The complex ROS-mediated regulation of neutrophil IL-1β secretion might constitute a physiological mechanism to control IL-1β-dependent inflammatory processes where neutrophils play a crucial role.Keywords: Caspase-1 r IL-1β r NADPH-oxidase r Neutrophil r Reactive oxygen species Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionNeutrophils represent the first line of defense against bacterial and fungal infections. Their pivotal role is highlighted by recurCorrespondence: Dr. Analía S. Trevani e-mail: analiatrevani@yahoo.com.ar rent infections in individuals suffering from neutrophil functional disorders or neutropenia [1]. Neutrophils kill microbes by the release of destructive molecules such as proteases and highly reactive oxygen species (ROS), and can also produce a variety of proteins, including cytokines, chemotactic molecules, and other mediators that are involved in their effector functions [2]. However, the microbicidal effectiveness of neutrophils is sometimes obscured by the damage suffered by adjacent healthy tissues; this is a price that has to be paid to contain potentially C 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2013. 43: 3324-3335 Innate Immunity 3325 life-threatening situations [3]. Although infections are the major triggers of neutrophil recruitment, many different sterile stimuli, including mechanical trauma, ischemia, toxins, minerals, crystals, and chemicals also lead to neutrophil accumulation in the tissues. In these situations, neutrophils may contribute to inflict collateral damage on otherwise healthy cells [3]. Interleukin-1 beta (IL-1β) is a key cytokine involved in the development of neutrophilic inflammation induced either by microbial or sterile inflammatory stimuli. It is a potent multifunctional proinflammatory cytokine, whose activity is controlled at the le...

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