ObjectiveTo construct and evaluate a mouse model that simulates the pathological progression of immune checkpoint inhibitor-associated pneumonitis (CIP), in order to address the critical issue of the lack of standardized animal models in this research field. MethodsThirty-five SPF-grade 6-week-old male C57BL/6J mice were randomly assigned to a control group (n=5), a bleomycin (BLM) group (n=15), and a BLM+programmed death-1 (PD-1) monoclonal antibody (BLM+PD-1) group (n=15). Corresponding drugs were administered via intraperitoneal injection for intervention. The general condition, body weight changes, survival rate, and pulmonary histopathological alterations were systematically monitored. ResultsCompared with the BLM group, the BLM+PD-1 group exhibited significantly more severe pulmonary fibrosis, characterized by progressive body weight loss and more severe deterioration of general conditions. Histopathological examination showed that pulmonary inflammation was alleviated 4 weeks post-modeling in the BLM group. In contrast, pulmonary lesions continued to worsen in the BLM+PD-1 group, with no evidence of resolution of inflammation 28 days post-modeling. Quantitative immunohistochemical analysis revealed that the positive expression rate of interleukin-17A (IL-17A) in lung tissues reached 34.28% in the BLM+PD-1 group 14 days post-modeling, which was markedly higher than that in the BLM group (24.02%, P < 0.000 1). The positive expression rate of α-smooth muscle actin (α-SMA) was 12.40% in the BLM+PD-1 group 14 days post-modeling, nearly twice the level in the BLM group (5.87%). 28 days post-modeling, the positive expression rate of α-SMA remained at 7.72% in the BLM+PD-1 group, while it declined to 3.38% in the BLM group. ConclusionThe addition of a PD-1 inhibitor to bleomycin treatment accelerates the progression of pulmonary interstitial fibrosis and effectively recapitulates the pathological process of lung injury and fibrosis driven by aberrant immune activation during clinical immunotherapy. Accordingly, this study successfully establishes a dynamic CIP animal model recapitulating the progression from early inflammatory response to pulmonary fibrosis. This model addresses the critical shortage of animal models for this condition and offers an experimental platform for further mechanistic studies and the development of therapeutic strategies.