Vacuolation, rosette formation, and membrane ruffling were hallmarks of AM activation, correlating strongly with serum ACE and sIL-2R but not with the BALF CD4/CD8 ratio.<h4>Conclusion</h4>AM enlargement and activation features are quantitative, reproducible surrogates of disease activity in pulmonary sarcoidosis. This evidence concerns the gene ACE and pulmonary sarcoidosis.