Studies in animals suggest that the initial activation of unprimed ("naive") T lymphocytes by inhaled antigens may occur outside the lung with later recruitment to the lung. If this is true all lymphocytes present in the lung should show evidence of prior activation. To test this hypothesis for lymphocytes present on the alveolar surface, the expression of surface antigens, which distinguish unprimed from previously activated cells (CD45RA, CD29, Leu-8), were measured on T lymphocytes recovered from blood and bronchoalveolar lavage fluid from normal subjects and patients with sarcoidosis. Few T lymphocytes from the lavage fluid of normal subjects and patients with sarcoidosis expressed the Leu 8+ or CD45RAbright phenotype expected for "naive" cells; more cells had the CD29dull phenotype expected for "naive" cells, though five of eight subjects had under 2% of such cells. These findings support the conclusion that the only T lymphocytes present on the surface of the respiratory tract are those recognising antigens that have been previously encountered by the individual. Further studies are required to determine whether "naive" T lymphocytes are present in other lung compartments.
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