Endobronchial biopsy specimens from control, moderate asthmatic, and severe asthmatic patients stained with antiretinoblastoma (anti-Rb) antibody, a marker of cell proliferation. Rb-positive cells stain brown. There is a significant increase in Rb-positive epithelial cells as asthma severity increases. There is also an increase in the number and size of goblet cells (GB) in the epithelial layer as asthma severity increases. Mag = 40x.
