The onset of MWCNT-induced fibrosis is characterized by Th2-type responses following the initial acute inflammation, which is manifested as an induction in e.g., IL4, IL5 and IL13 in the BAL and the lung of exposed animals (29–33) as well as elevated levels of IL4 and IL5 in sputum of MWCNT-exposed workers (34), and is suggested to involve macrophage phenotypic changes (35–38). Here, IL5 is linked to fibrosis.