Taken together, our findings suggest that administration of FICZ to BLM-induced pulmonary fibrosis model mice increased the number of CD4+Foxp3+ Tregs and reduced the number of CD4+IFNγ+ and γδ+IL-17A+ T cell populations in the lungs and contributed to improve or attenuate lung inflammation induced by BLM. Here, CD4 is linked to pulmonary fibrosis.