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 spe cimens, HP accompanied by lung fibrosis (fibrosis group), and HP unacc ompanied by lung fibrosis (nonfibrosis group). The fibrosis group comp rised bird fancier's lung and HP of unknown etiology, whereas the nonf ibrosis group mainly comprised summer-type HP. Comparison of results o f pulmonary function tests between these two groups confirmed a restri ctive impairment in the fibrosis group. Analyses of cellular component s of bronchoalveolar lavage (BAL) fluids revealed lymphocytes, especia lly CD8+ T lymphocytes, were significantly increased in the nonfibrosi s group in comparison with the fibrosis group, whereas CD4+ T cells we re increased to the same level in the both groups. Analyses of the ons et of disease showed that acute onset was observed mainly in nonfibros is group and strongly correlated with increased CD8+ T lymphocytes in BAL fluids, while insidious onset was related to lung fibrosis and rel atively increased CD4+ T lymphocytes in BAL fluids. These findings rai se the possibility that highly elevated CD8+ T cells might have a prot ective effect on pulmonary fibrosis or that relatively increased CD4T cells might play an important role in the pathogenesis of pulmonary fibrosis of HP at the chronic phase.