Our study highlighted two important findings: 1) immune responses to Pseudomonas and/or its exotoxin actually protect mice from bleomycin-induced pulmonary fibrosis; 2) neutralizing antibodies against Pseudomonas and/or its exotoxin do not hamper the therapeutic effect of IL13-PE delivered into the fibrotic lung. This evidence concerns the gene IL13 and pulmonary fibrosis.