Scientists made two mouse models of rosacea using the peptide LL-37—one with short exposure and one with long exposure—to see how the skin and immune system change over time. The long‑term model showed thicker skin, more blood vessels, bigger oil glands, and activation of both innate and adaptive immunity, while the short‑term model mainly affected innate immunity.

It is well recognized that developing new animal models, refining the existing mouse models, and thoroughly characterizing their features are essential for gaining a deeper understanding of rosacea pathogenesis and for advancing therapeutic strategies in this direction. Accordingly, we aimed to characterize the pathological features of a long-term LL-37-induced mouse model of rosacea and to compare the disease manifestations and pathophysiological characteristics between short-term and long-term LL-37-induced models. A key focus was to investigate differential gene expression and the underlying mechanisms of immune system dysregulation in these models. We comparatively assessed skin lesion manifestations, the extent of inflammatory infiltration, sebaceous gland alterations, fibrosis, and angiogenesis in both models. Assessments were performed using photographic documentation, hematoxylin-eosin (HE) staining, Van Gieson's (VG) staining, immunohistochemistry, and Western blotting. Furthermore, we employed RNA sequencing to analyze differential gene expression in mouse skin. The RNA sequencing data were validated using immunofluorescence staining and Western blotting, with a specific focus on gene variations and mechanisms related to immune system dysregulation. Mice subjected to long-term LL-37 induction developed rosacea-like pathological features, including angiogenesis, thickened skin tissue, and sebaceous gland hypertrophy. In the short-term LL-37-induced model, immune dysregulation primarily involved the innate immune response. However, long-term LL-37 induction resulted in significant activation of both innate and adaptive immune responses. The long-term LL-37-induced mouse model offers a valuable animal model for the detailed investigation of the pathological mechanisms driving moderate-to-severe rosacea with prolonged disease duration. Importantly, this model provides a significant experimental foundation for exploring the potential role of immune system dysregulation in rosacea pathogenesis.