Lung fibrosis in hypersensitivity pneumonitis. Association with CD4+ but not CD8+ cell dominant alveolitis and insidious onset.

Seventeen cases of hypersensitivity pneumonitis (HP) at a symptomatic phase were categorized into two groups based on computed tomographic (CT) findings and histologic features of transbronchial lung biopsy specimens, HP accompanied by lung fibrosis (fibrosis group), and HP unaccompanied by lung fibrosis (nonfibrosis group). The fibrosis group comprised bird fancier's lung and HP of unknown etiology, whereas the nonfibrosis group mainly comprised summer-type HP. Comparison of results of pulmonary function tests between these two groups confirmed a restrictive impairment in the fibrosis group. Analyses of cellular components of bronchoalveolar lavage (BAL) fluids revealed lymphocytes, especially CD8+ T lymphocytes, were significantly increased in the nonfibrosis group in comparison with the fibrosis group, whereas CD4+ T cells were increased to the same level in the both groups. Analyses of the onset of disease showed that acute onset was observed mainly in nonfibrosis group and strongly correlated with increased CD8+ T lymphocytes in BAL fluids, while insidious onset was related to lung fibrosis and relatively increased CD4+ T lymphocytes in BAL fluids. These findings raise the possibility that highly elevated CD8+ T cells might have a protective effect on pulmonary fibrosis or that relatively increased CD4+ T cells might play an important role in the pathogenesis of pulmonary fibrosis of HP at the chronic phase.