Establishment and multidimensional characterization of a sustained rat model of granulomatous mastitis using...

Granulomatous mastitis (GM) is a chronic inflammatory breast disease characterized by non-caseating granulomatous inflammation and a prolonged, recurrent clinical course. Basic research on GM has been limited by the lack of well-characterized and reproducible animal models. This study aimed to establish and characterize a modified rat model of GM using sequential antigen-adjuvant stimulation. Human GM lesion tissue homogenate was used as the antigen source. Female Sprague-Dawley rats were assigned to Control, complete Freund's adjuvant (CFA), incomplete Freund's adjuvant (IFA), and Mix groups. Different antigen-adjuvant stimulation protocols were applied on days 0 and 14. Mammary lesions were evaluated by gross observation, breast inflammation scoring, infrared thermography, ultrasonography, H&E staining with semi-quantitative GM-like histopathological severity scoring (GM-HSS), serum inflammatory cytokine detection, qRT-PCR analysis, and flow cytometry. The CFA group developed obvious GM-like mammary lesions at the early stage, but lesion-related indicators and GM-HSS decreased at the later stage. The IFA group showed relatively mild changes. In contrast, the Mix group maintained prominent mammary masses, elevated mammary surface temperature, higher inflammation scores, persistent hypoechoic intramammary lesions, marked histopathological injury, and high GM-HSS at the endpoint. The Mix group also showed sustained elevation of serum inflammatory cytokines and mammary inflammatory gene expression, accompanied by increased CD86/CD163 and IL-17A/Foxp3 ratios. Sequential stimulation with CFA- and IFA-emulsified GM tissue homogenate established a rat model with sustained GM-like lesions that reproduced key inflammatory, imaging, histopathological, and immune-related features of GM. This model may provide a useful platform for future mechanistic and therapeutic studies.