IL5 and fibrosis: Moreover, infected KO rats displayed a marked decrease in the levels of both Th1- (IFN-γ) and Th2-associated cytokines (IL-4, IL-5) at all time points post-infection, except with IL-2 and IL-13 (Fig 3C), both of which play an important role in granuloma and fibrosis development [26,27].