NLRP3 inflammasome expression in idiopathic pulmonary fibrosis and rheumatoid lung

In this study we investigated the implication of NLRP3 inflammasomes in the pathogenesis of idiopathic pulmonary fibrosis (IPF) and rheumatoid arthritis-usual interstitial pneumonia (RA-UIP). NLRP3 inflammasome activation at baseline and following stimulation with lipopolysaccharide/ATP was evaluated by measuring interleukin (IL)-1 beta and IL-18 levels released in the bronchoalveolar lavage fluid (BALF) fluid and by cultures of BALF cells. IL-1 beta and IL-18 levels were significantly elevated in the BALF and BALF macrophage cultures from RA-UIP patients, consistent with pre-existing inflammasome activation in these patients. In contrast, in IPF, BALF levels of IL-1 beta were significantly less elevated relative to RA-UIP and IL-18 was lower than controls. Furthermore, upon inflammasome stimulation, IPF BALF macrophage cultures failed to upregulate IL-1 beta and partly IL-18 secretion, in contrast to controls, which showed robust IL-1 beta and IL-18 upregulation. Interestingly, RA-UIP BALF cell cultures treated with lipopolysaccharide/ATP showed a potent stimulation of IL-18 secretion but not IL-1 beta, the latter being already elevated in the unstimulated cultures, while examination of the intracellular IL-1 beta levels in RA-UIP BALF cells upon NLRP3 inflammasome stimulation showed a significant upregulation of IL-1 beta suggesting the NLRP3 pathway could be further activated. Taken together, our results suggest distinct inflammasome activation profiles between autoimmune and idiopathic lung fibrosis.