IL4 and pulmonary fibrosis: Previously, we reported that IL-4-producing NKT cells play a protective role in SR-induced hypersensitivity pneumonitis (HP) by suppressing the IFN-γ-producing neutrophils, thereby decreasing SR-specific IgG levels, while NKT cells attenuate bleomycin-induced pulmonary fibrosis (BIPF) by producing IFN-γ [7], [32].