Localization of activated, phosphorylated STAT3 in fibroblast foci and overlying bronchiolar epithelium in idiopathic pulmonary fibrosis (IPF) lungs.

Representative immunohistochemistry for α-SMA, phosphorylated (p)-STAT3 (Y705) and cytokeratin-5 (KRT5) in (A) IPF- and (B) normal donor lung tissue. (C) Representative immunohistochemistry for KRT5, survivin, α-SMA, p-STAT3, and HDAC4 in serial sections of IPF-lung tissue. (A) In IPF, the antibody for p-STAT3 revealed nuclear staining in myofibroblasts of fibroblast foci (FF, indicated by dashed arrows and α-SMA-staining) as well as in abnormal bronchiolar basal cells overlying FF (indicated by arrows and KRT5 staining). (B) Normal donor lungs indicated no or minimal staining in the interstitium as well as alveolar epithelium. Bronchial epithelium (indicated by hashmark) showed only faint immunoreactivity for p-STAT3. (C) Induction of p-STAT3 is observed in fibroblast foci (indicated by dashed arrows) and overlying abnormal bronchiolar epithelium (indicated by arrows and KRT5 expression), as well as in bronchioles (indicated by hashmark) in IPF, and coincided with survivin and HDAC4 overexpression in these areas. Smooth muscle cells of IPF lungs (indicated by asterisk) also revealed nuclear p-STAT3 and survivin induction.