Immunostaining. Immunoreactivity within the bronchial epithelium for EGFR after air and diesel exhaust exposure. Positive staining (brown) can be seen on the basolateral border of the columnar cells after exposure to air (panel A) and throughout the epithelium following exposure to diesel exhaust (panel B). Arrows show intracytoplasmatic Tyr 1173 immunostaining in the basoperinuclear region of columnar cells and basolateral border of basal cells (panel C After air exposure and panel D after DE exposure). Panel E: Primary IgG antibody serving as a negative contol. Panel F demonstrates the normal brown DAB staining in panel D which is presented by red color following computer-aided selection and quantification by the image analyser program.