[Pulmonary immunology]

Knowledge of pulmonary immunology is essential to the understanding of certain respiratory diseases. The airways and alveolar zones may be seen separately and in contrast on the basis of the immune system of the lung. Broadly speaking, within the airways there are mast cells, polynuclear eosinophil and lymphocytes. By contrast in the alveolar zones there are macrophages and lymphocytes which are either free in the alveolar lumen or present in the pulmonary interstitial tissue, as well as lymphocytes. In most instances inhaled antigens are not at the origin of an immune response, whether deposited on the mucociliary surface or phagocytosed by the alveolar macrophage. The BALT play a probably primordial role in immune information within the tracheobronchial epithelium. The immune response occurs in the airways in the form of the secretion of secretory A immunoglobulins, whilst in the alveolus phagocytosis by the alveolar macrophage represents the principal means of defence. Such phagocytosis only rarely gives rise to inflammatory phenomena which would impair alveolar function. Finally, the collection of bronchoalveolar washings is a technique which may be used to collect immunocompetent cells of principally alveolar origin for the purpose of their study.