Myeloid cell-derived NLRP3 is dispensable for silica-induced pulmonary inflammation and pathology.

Abstract

Silicosis is a progressive occupational lung disease marked by persistent silica-induced inflammation and irreversible pulmonary fibrosis. The NLRP3 inflammasome, an innate immune sensor, has been implicated as a key driver of silica-triggered inflammation and fibrosis in preclinical models. However, the specific role of NLRP3 in immune cells, particularly within myeloid cells (monocytes, macrophages and neutrophils), remains poorly defined. In this study, we investigated the in vivo contribution of myeloid-derived NLRP3 to silica-induced lung pathology using a conditional NLRP3 knockout mouse model (LysMNlrp3). These mice exhibited efficient deletion of NLRP3 in both resident and infiltrating lung myeloid cells. Following intranasal delivery of 2 mg of silica, NLRP3 expression was upregulated in myeloid cells by day 3. Despite upregulation of NLRP3 in myeloid cells by day 3, early inflammasome activation in the tissue and BAL, including caspase-1 cleavage and IL-1β and IL-18 secretion, remained intact. During the chronic phase (days 14 and 28), myeloid NLRP3 deletion did not mitigate hallmark features of silicosis, including alveolitis, structural lung damage, airway remodeling or peribronchial alpha-smooth muscle actin expression. Furthermore, the formation and size of silicotic nodules were unaffected. These findings indicate that NLRP3 expression in myeloid cells is not essential for the development of silica-induced pulmonary inflammation, tissue damage or fibrosis. This work highlights the need to explore alternative cellular sources and mechanisms of NLRP3-driven pathology in silicosis.