RAG2 and pulmonary fibrosis: Remarkably, although the administration of bleomycin has established an IPF mouse model that has been widely used in the study of IPF disease, we also need to use over genetic alteration or knockout of specific genes (e.g., knockout of Ifgr1/Rag2-related genes) to establish a pulmonary fibrosis model to gain insights into spontaneous pulmonary fibrosis, to study the pathogenesis of IPF and to search for new therapeutic approaches (35).