Activated and memory alveolar T-lymphocytes in idiopathic eosinophilic pneumonia

To investigate the possible involvement of T-lymphocytes in the immunopathogenesis of idiopathic eosinophilic pneumonia (IEP), we have evaluated the phenotypic characteristics both of peripheral blood and alveolar lymphocytes in six patients with symptomatic IEP, and in 24 healthy nonsmokers as controls, by employing bronchoalveolar lavage (BAL), monoclonal antibodies, and flow-cytometry. In IEP, total and differential cell counts showed a mild alveolitis with an increase of eosinophil percentage and number; the alveolar lymphocyte count was also increased. In BAL, the total number both of CD4+ and CD8+ lymphocytes was significantly raised; CD4+ cells expressed early (CD25) activation antigens. The analysis of CD45R0, CD45RA and CD62L coexpression in IEP patients, when compared to healthy controls, revealed an accumulation of alveolar CD4+ cells showing phenotypic repertoire usually expressed by memory T-cells (CD45R0+, CD45RA-, CD62L-). CD8+ alveolar lymphocytes did not show any significant increase of activation antigen coexpression. Circulating lymphocytes were not significantly increased and showed only a significantly higher CD25 expression. These data suggest that a pivotal role is played by activated and memory CD4+ alveolar lymphocytes in IEP patients.