An oropharyngeal exposure of MWCNTs induced (a) lung inflammation, evidenced by increased neutrophils in the BAL fluid; (b) lung fibrosis, shown by increased collagen deposition and granuloma formation; and (c) reduced lung functions, indicated by increased elastic rigidity, reduced compliance, and increased Newtonian resistance in C57BL/6, but not the mast cell-deficient KitW-sh or the ST2−/− (ST2 KO), mice. Here, IL1RL1 is linked to pulmonary fibrosis.