Rat Model of Granulomatous Mastitis

Abstract

Background: Granulomatous mastitis (GM) is an immune-related, clinically refractory disease, the translational research of which has been hindered by the lack of animal models. Establishing a stable rat model of GM is critical for elucidating its mechanisms and developing therapeutic approaches.

Methods: The first batch of rats was randomly divided into a normal group, a low-dose group (0.2 mL), a middle-dose group (0.4 mL), and a high-dose group (0.8 mL). Except for the normal group, the remaining groups were subjected to model establishment using a tissue homogenate-complete Freund's adjuvant (CFA) suspension. The optimal dose was determined based on gross morphology, mammary inflammation index, and histopathological evaluation. The second batch of rats was modeled using the optimal dose, with a comparable number of normal rats as controls. At 7, 14, 21, and 28 days post-modeling, mammary gland appearance, histomorphology, and serum/tissue mRNA expression levels of key inflammatory factors (TNF-α, IL-1β, IFN-γ, IL-2) were observed.

Results: Rats in the middle-dose group exhibited characteristic features of human GM, including gross morphological changes such as breast swelling, ulceration, and fistula formation. Histologically, granulomas characterized by epithelioid cells and Langhans multinucleated giant cells, along with persistent inflammatory cell infiltration, were observed. Compared with the parallel normal group, the expression levels of IL-2, IL-1β, TNF-α, and IFN-γ were significantly elevated in the model group, with their expression fluctuating over time.

Conclusion: The 0.4 mL tissue homogenate-CFA injection method successfully induced a stable, reproducible, and long-lasting rat model that closely mimics human GM. This model provides a robust foundational platform for future research.

Keywords: animal model; autoimmunity; granulomatous mastitis; tissue homogenate-CFA injection method.

Figure 1

Changes in body mass of rats in different groups on the day of modeling (0 days), and 3, 7, and 14 days after modeling. Values at 0, 3, and 7 days represent mean ± standard deviation, while the value at 14 days is the median *P < 0.05 compared to the parallel normal group.

Figure 2

Mammary gland appearance of rats in each group 14 days after modeling. The size of breast lumps and the degree of local inflammation followed the order: high-dose group > middle-dose group > low-dose group. The lumps in the low-dose group subsided the fastest, and the mammary gland appearance was almost indistinguishable from the normal group 14 days after modeling. The high-dose group showed the most destructive lumps, with large areas of skin ulceration and purulent discharge.

Figure 3

Effects of different doses of oil-in-emulsion suspension on histopathological changes in rat mammary gland tissue 14 days after modeling. HE staining. Upper images: Magnification = 100× (scale bar = 200um); Lower images: Magnification = 400× (scale bar = 50um).

Figure 4

Changes in body weight of rats in the normal and model groups over time. Values are mean ± standard deviation. **P < 0.01 vs the parallel normal group.

Figure 5

Appearance of the mammary glands in the model group at 7, 14, 21, and 28 days after modeling.

Figure 6

B-ultrasound morphology of the mammary glands in the model group at 7, 14, 21, and 28 days after modeling. At 7 days after modeling, obvious irregular hypoechoic areas were visible, with anechoic areas inside, and strong echo bands with posterior acoustic shadowing or attenuation were visible below; at 14 days, the hypoechoic areas shrank, and the internal anechoic dark fluid areas expanded; at 21 days, both the hypoechoic and anechoic areas shrank; at 28 days, the hypoechoic areas were significantly reduced with blurred boundaries, and a small amount of residual anechoic areas were visible.

Figure 7

Histopathological changes in breast tissue of rats in the model group at 7, 14, 21, and 28 days after injection with 0.4mL of oil-in-emulsion suspension. HE staining. Magnification = 100× (scale bar = 200um); Magnification = 400× (scale bar = 50um).

Figure 8

Changes in serum inflammatory factor expression in rats of each group. (A): IL-2 expression, (B) IL-1β expression, (C) TNF-α expression, (D) IFN-γ expression. **P < 0.01 vs parallel normal group; ^#P < 0.05 vs 7d in this group.

Figure 9

Changes in mRNA expression of inflammatory genes in rat mammary tissue in each group. (A): IL-2 expression, (B) IL-1β expression, (C) TNF-α expression, (D) IFN-γ expression. **P < 0.01 vs parallel normal group; ^#P < 0.05 vs 7d in this group; ##P < 0.01 vs 7d in this group.