Immunohistochemistry for smooth muscle actin in lung at birth.

In the normal lung at 6 hours after birth, a specific smooth muscle actin (SMA) signal (green) is present in myofibroblasts at the saccular tips (tips) and vascular smooth muscle cells from a large blood vessel (V) in the left panel (green fluorescence) and the right panel (green despite merger with red autofluorescence). Nonspecific yellow signal (green merged with red autofluoresecence) is present in hematopoietic cells in large blood vessels. In the Klf4 null lung, however, the specific green SMA signal is only present in vascular smooth muscle cells from a large blood vessel (V). Cells in saccular tips in the left panel are yellow after merger with red autofluorescent signal in the right panel denoting non-specific signal likely originating from hematopoietic cells in small blood vessels within the lung interstitium as in large blood vessels.