Immunopathology of Experimental Bronchiectasis

In human bronchiectasis, the bronchial wall is the seat of abnormal mononuclear cell infiltration, which suggests the presence of a cell-mediated immune reaction. The histopathology of a recently devised animal model of experimental bronchiectasis resembles that of the human disease. We have investigated its immunohistology to validate the similarity to that of human bronchiectasis in order to provide a model for the study of cellular immune aspects of the pathogenesis of bronchiectasis. The immunohistology of the bronchial wall mononuclear cell population in experimental rat bronchiectasis was compared with that in control and normal rats. The control rats did not develop bronchiectasis, and the composition and distribution of mononuclear cells in the bronchial wall were similar to those of normal animals. In the rats developing bronchiectasis, there was infiltration of T lymphocytes, macrophages, and dendritic cells (as defined by monoclonal antibodies) in all compartments of the lung, particularly in the bronchial wall and around vessels. The bronchus-associated lymphoid tissue was disrupted by heavy infiltration of T cells, and follicular aggregates of T lymphocytes were seen deeper in the lung parenchyma. Expression of Ia antigen increased in the bronchial epithelium and in large numbers of mononuclear cells throughout the lung. These findings suggest that a cell-mediated immune response appears during the development of experimental bronchiectasis in this rat model. This cellular immune response is similar to that described in human bronchiectasis and may enable this animal model to be used in defining the role of cellular immunity in the pathogenesis of bronchiectasis.