Light micrograph of respiratory epithelium basal cells. This immunohistochemical stain for p40 protein colours the basal cells brown, showing them at the bottom of the epithelial cell layer. The cells on top of the basal cells are ciliated columnar respiratory epithelial cells. Interspersed goblet cells (oval white spaces) are also seen. Subepithelial connective tissue is present beneath the basal cells. Immunohistochemically stained tissue section. Magnification: 200x when printed at 10cm.