Immunologic markers and fine structure of alveolar cells in germfree pigs.

The objective of this study was to evaluate neonatal development of alveolar cells without any antigenic stimulation. The cells obtained by bronchoalveolar lavage from newborn and germfree Minnesota miniature piglets were characterized ultrastructurally and using different markers of pig lymphocytes and macrophages. Alveolar cells from newborn animals did not express any immunologic markers or phagocytic activity. Cells of the pulmonary immune system appeared in the airways at the twelfth hour, phagocytosing macrophages within the first day of postnatal life. Fc receptors were expressed sooner than complement receptors. Almost all lymphocytes were null cells. Macrophages and lymphocytes immigrated into alveolar spaces independently of external antigenic stimuli.