Abstract
A morphological study of the bronchus-associated lymphoid tissue (BALT) of normal rats, rabbits and cattle was performed with light and electron microscopy. Remarkable morphologic similarities of the BALT in these animals were recognized. The BALT was fundamentally divisible into 4 different areas: (1) the lymphoepithelium, (2) the subepithelial zone of lymphoid mass, (3) the central area of lymphoid mass, and (4) the peripheral zone of lymphoid mass.
Inhaled dust and alveolar macrophages containing phagocitized materials of various forms and sizes were occasionally observed between the epithelial cells and in the crypt of the lymphoepithelium. Lymphocytes are occasionally found migrating between not only epithelial cells of the lymphoepithelium but also endothelial cells of the high endothelial venules and the lymphatic vessels in the BALT.
Lymphocytes in the BALT come into contact with alveolar macrophages containing phagocitized antigen as a first line of defense and thus may be expected to play an important role in the immunologic defense mechanisms of the respiratory tract.
