Our conclusion is based on the observation that mammary stromal fibroblasts derived from mastitic cows show inflammation-specific changes compared with those from cows without mastitis, including the following: relatively abundant lysosomal vacuoles; enhanced activities as indicated by FAP and α-SMA expression; increased proliferation capacity; elevated TGF-α and IL6 secretion; upregulated inflammation-related genes; as well as inhibitory effects on the proliferation and β-casein secretion of epithelial cells and stimulatory effects on the TGF-α and IL6 expression in epithelial cells. This evidence concerns the gene ACTA1 and mastitis.