Résumé
Background: Inflammasome-activated IL-1β plays a major role in lung neutrophilic inflammation induced by inhaled silica. However, the exact mechanisms that contribute to the initial production of precursor IL-1β (pro-IL-1β) are still unclear. Here, we assessed the implication of alarmins (IL-1α, IL-33 and HMGB1) in the lung response to silica particles and found that IL-1α is a master cytokine that regulates IL-1β expression. Methods: Pro-and mature IL-1β as well as alarmins were assessed by ELISA, Western Blot or qRT-PCR in macrophage cultures and in mouse lung following nano-and micrometric silica exposure. Implication of these immune mediators in the establishment of lung inflammatory responses to silica was investigated in knockout mice or after antibody blockade by evaluating pulmonary neutrophil counts, CXCR2 expression and degree of histological injury. Results: We found that the early release of IL-1α and IL-33, but not HMGB1 in alveolar space preceded the lung expression of pro-IL-1β and neutrophilic inflammation in silica-treated mice. In vitro, the production of pro-IL-1β by alveolar macrophages was significantly induced by recombinant IL-1α but not by IL-33. Neutralization or deletion of IL-1α reduced IL-1β production and neutrophil accumulation after silica in mice. Finally, IL-1α released by J774 macrophages after in vitro exposure to a range of micro-and nanoparticles of silica was correlated with the degree of lung inflammation induced in vivo by these particles. Conclusions: We demonstrated that in response to silica exposure, IL-1α is rapidly released from pre-existing stocks in alveolar macrophages and promotes subsequent lung inflammation through the stimulation of IL-1β production. Moreover, we demonstrated that in vitro IL-1α release from macrophages can be used to predict the acute inflammogenic activity of silica micro-and nanoparticles.