2.5. Masson's trichrome stain

The slide was put in Masson's ponceau acid complex solution for 5 min of reaction and washed for 1 min. Then the slide was immersed in 2% glacial acetic acid solution I and II for 1 min, rinsed for 15 min, differentiated in 1% phosphomolybdic acid solution for 5 min and washed under running water for 1 min. Next, the slide was placed in bright green dye solution for 5 min, washed for 1 min, immersed in 2% glacial acetic acid solution I and II for 1 min, and rinsed for 15 min. After dehydration and blocking, the slide was observed under a light microscope and scored by a blind method. According to the previously revealed rating (0–4 points) [32,33], 0 point represents no increase in connective tissue; 1 point represents that the thinner fibers occupy less than 50% of the inflammatory cell infiltration localization, and no thick collagen; 2 points represent that the thinner fibers occupy more than 50% of the inflammatory cell infiltration localization, and no thick collagen; 3 points represent that all the inflammatory cell infiltration localization is filled with the thinner fibers, and the amount of thick collagen is between 10% and 49%; 4 points represent that all the inflammatory cell infiltration localization is filled with thinner fibers, and the amount of thick collagen exceeds 50%. Five high-power visual fields from each section were observed, and the average value was taken as the severity of fibrosis score (F score). The average value of all sections on the same side of one group was regarded as the fibrosis score of the group. The experiment was run in triplicate.