Different lymphocyte subpopulations have been evaluated in bronchoalveolar fluid and blood obtained from six patients with active and six with inactive pulmonary sarcoidosis and from six normal subjects by means of two recently described monoclonal antibodies, 5/9 and MLR4. The percentages of OKT4 positive (helper) and OKT8 positive (suppressor) T cells were also determined. Patients with active sarcoidosis had significantly higher proportions of 5/9 positive T cells in the bronchoalveolar fluid than patients with inactive disease (p less than 0.01) or normal subjects (p less than 0.001). In contrast, the proportions of 5/9 positive blood T cells were similar in the three groups studied. Patients with active sarcoidosis had also a greater proportion proportion of MLR4 positive T lymphocytes in bronchoalveolar fluid than patients with inactive disease or normal subjects (p less than 0.01 for each comparison), but similar proportions of MLR4 positive blood T cells were found in each group. The ratio of 5/9 positive to MLR4 positive T cells was higher in the bronchoalveolar fluid (but not in the blood) in patients with either active or inactive sarcoidosis than in normal subjects. These observations suggest that the MLR4 negative fraction rather than the MLR4 positive fraction of the 5/9 positive T cells is preferentially expanded in the lungs of patients with pulmonary sarcoidosis and may indicate a secondary role for the MLR4 positive T cells in producing lung injury in this disorder. Comparisons of the OKT4 positive and 5/9 positive T cells showed that in patients with active disease most of the lung T lymphocytes expressed both the OKT4 and the 5/9 surface antigens, so the 5/9 monoclonal antibody may be considered a good marker of activity in this disorder. Pulmonary sarcoidosis may be characterised by the preferential expansion of helper T cell subsets at sites of disease activity.
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