Allergic diseases in the lungs

Four basic immune reactions in the lung are fundamental to our understanding of allergic lung diseases. The first, immediate hypersensitivity, principally involves airway obstruction because of hypersecretion and bronchospasm. Resulting roentgenographic changes are those of large and small airway disease. The second reaction, cytotoxic antibody-mediated disease, produces air space filling by hemorrhage. The third form, immune complex-mediated hypersensitivity, causes mixed patchy consolidation and interstitial roentgenographic patterns caused by inflammation stimulated by antigen-antibody complexes. Fourth, cell-mediated immunity usually produces a granulomatous reaction, roentgenographically manifest by nodules, masses, and enlarged lymph nodes. Applying our understanding of these four basic reactions permits understanding the common allergic disease of the lungs: hypersensitivity pneumonitis, asthma, allergic bronchopulmonary fungal disease, chronic eosinophilic pneumonia, hypereosinophilic syndrome, Goodpasture's syndrome and idiopathic pulmonary hemosiderosis (IPH), Wegener's granulomatosis, and allergic granulomatosis (Churg-Strauss disease). The clinical, pathologic, and roentgenographic manifestations of these diseases are explained and related to the basic immune mechanisms.