Regulation of IL-1beta release by human neutrophils

GABELLONI, MARIA LAURA; FUXMAN BASSS, JUAN; GEFFNER, JORGE; OLEASTRO, MATIAS; JANCIC, CAROLINA; TREVANI, ANALIA

Buenos Aires

Congreso; First French-Argentine Immunology Congress; 2010

IL-1beta is a pro-inflammatory cytokine which is released after proteolytic processing of pro-IL-1beta. Stimulation of NOD-like receptors leads to the formation of an inflammasome, which recruits and activates caspase-1, the enzyme responsible for the processing of pro-IL-1beta. In previous studies we demonstrated by ELISA that human neutrophils release IL-1beta by a caspase-1-dependent pathway. Because the mechanisms that lead to IL-1beta release remain controversial and have not been defined in neutrophils, this study was conducted to address this issue. We confirmed by confocal microscopy and flow cytometry that neutrophils synthesize IL-1beta in response to LPS (200 ng/ml), crystals of monosodium urate (MSU; 200 µg/ml) and LPS + 2.5 mM ATP (LPS+ATP) or LPS + MSU. IL-1beta release evaluated by ELISA was inhibited by the proteasome inhibitor MG-132 (% inhibition >70 for all the agonists; p<0.05; n=3), suggesting a role for NF-kB in the mechanisms that lead to IL-1betasecretion. Neutrophils from three X-linked chronic granulomatous disease (CGD) patients, which are unable to generate NADPH-dependent reactive oxygen species (ROS), released IL-1beta only in response to LPS+MSU (pg/ml IL-1beta: 410±4) indicating that at least for some agonists ROS play a role in IL-1beta secretion. However, treatment with xanthine/xanthine oxidase (X/XO), a O2?- generating system, partially inhibited IL-1beta release in neutrophils from healthy donors (% inhibition >41% for all stimuli; p<0.05, n=6) and in CGD neutrophils treated with LPS+MSU (% inhibition: 74%), suggesting that ROS also exert a negative control over IL-1beta release. Caspase-1 activation was not affected in healthy neutrophils by X/XO treatment, suggesting that ROS negative regulation is not exerted over inflammasome activation. Because ROS are suggested to induce NF-kB activation, our findings suggest that ROS might regulate neutrophil IL-1beta release by both stimulating IL-1beta transcription and negative controlling another step involved in the secretion.