Preventive effect of propylthiouracil administration uponpulmonary fibrosis development in HOCl-induced murine model ofsystemic sclerosis. Representative Masson'strichrome-stained section of lung examined by light microscopy:(A) Normal histology of a representative lung tissue fromSham mouse; (B) Representative lung section from HOCl mouse;(C) Representative lung section from HOCl + PTU mouse(Original magnification, ×10.); (D) Semiquantitativeanalysis of lung tissue graded by using the Ashcroft score, asdescribed in Methods. The degree of pulmonary fibrosis was evaluatedin Masson trichrome-stained sections by using the Ashcroft score(the grade of lung fibrosis was scored on a scale of 0 to 8 by usingthe following criteria: grade 0, normal lung; grade 1 to 2, minimalfibrous thickening of alveolar or bronchiolar wall; grade 3 to 4,moderate thickening of walls without obvious damage to lungarchitecture; grade 5 to 6, increased fibrosis with definite damageto lung structure; and grade 7 to 8, severe distortion of structureand large fibrous areas. Values are expressed as the mean and SD.*P < 0.001 versus Sham; #P < 0.001versus HOCl. HOCl group (n = 10), HOCl + PTU group (n = 10), Sham (n = 5).