Immunostaining for AMCase expression. A) Immunostaining for AMCase expression revealed minimal reactivity in the lungs of controls. B) Intense signal was demonstrated in airway epithelium (black arrow), particularly after 2 months of infection. C) Similar expression patterns in the airway epithelium (black arrow) and alveolar macrophages (white arrow) were also seen at 2 weeks. Original magnification 200× for all photomicrographs. Inset shows high magnification (original magnification 1000×) of immunoreactive cells that appear to be alveolar macrophages.