CELLULAR AND SUBCELLULAR LOCALIZATIONS OF ANNEXIN-I, ANNEXIN-IV, AND ANNEXIN-VI IN LUNG EPITHELIA

The cellular and subcellular localizations of annexins I, TV, and VI i n the rabbit tracheal and alveolar epithelia were studied by performin g immunofluorescence labeling on thin frozen sections of these tissues , using specific monoclonal antibodies. Annexin I was highly expressed by ciliated cells, where it was concentrated in the cilia but was als o present along the basolateral domain of the plasma membrane and in t he nuclei. It was also abundant in the cytoplasm of type IT pneumocyte s and alveolar macrophages. Either one or both of these alveolar cells might be capable of secreting a very small amount of annexin I, which was found to be associated with the surfactant layer. Annexin IV was synthesized by all the lung epithelial cells. It was associated with t he plasma membrane basolateral domain in ciliated cells and with eithe r the apical or basal domain of plasma membrane in type I pneumocytes, whereas it was cytoplasmic in goblet cells and type II pneumocytes. A nnexin VI was expressed only by alveolar endothelial cells, where it w as probably cytoplasmic. None of these three annexins seem to be expre ssed in the nondifferentiated tracheal basal epithelial cells.