Figure 3: Immunoperoxidase staining for IL-33 in human airways. (A) Control tissue from a patient with mild chronic obstructive pulmonary disease, showing minimal epithelial staining (note cytoplasmic staining of macrophages). (B) Airway tissue from an asthmatic patient, showing strong nuclear staining of bronchiolar epithelium. (C) Airway tissue from a patient with ABPA, showing nuclear staining of bronchiolar epithelium together with apical cytoplasmic staining (arrowheads) as well as cytoplasmic staining of plasma cells in the lamina propria (arrows). Original magnification ×400.