Immunology of the lower respiratory tract. Serial morphologic changes in the lungs and tracheobronchial lymph nodes of dogs after intrapulmonary immunization with sheep erythrocytes.

Sequential histologic changes in immunized and contralateral lung lobes, and ipsilateral and contralateral tracheobronchial lymph nodes were evaluated from dogs after intra-pulmonary immunization with sheep erythrocytes. In addition, changes in the relative numbers of unstimulated lymphocytes, activated lymphocytes, and plasma cells were determined for immunized and contralateral lung lobes by the use of bronchopulmonary lavage. Histologic evidence of an immune response occurred 2 days after immunization in ipsilateral tracheobronchial lymph nodes and on Day 5 in immunized lung lobes. Pulmonary lymphoid infiltrates appeared initially around pulmonary venules and veins. There was expansion of these infiltrates into alveolar spaces, where mixed mononuclear aggregates were formed in association with alveolar macrophages 7 days after immunization. A similar but attenuated and delayed response occurred within contralateral control lung lobes, although mononuclear aggregates were not found. Activated lymphocytes in lavage samples increased prior to histologic evidence of pulmonary lymphoid infiltrates. These results suggest that after intrapulmonary immunization the lung recruits circulating immunocytes produced in ipsilateral lung-associated lymph nodes as the source of specific antibody-forming cells in bronchoalveolar air spaces.