Maintenance of granuloma formation in pulmonary sarcoidosis by T lymphocytes within the lung.

Pulmonary granulomata of sarcoidosis are composed primarily of mononuclear phagocytic cells that are probably derived from blood monocytes. To evaluate the concept that recruitment of blood monocytes to the sarcoid lung is mediated by chemoattractants produced by immune effector cells within the lung, we obtained mononuclear cells from lung and blood of six patients with active pulmonary sarcoidosis, six normal subjects, and six patients with active idiopathic pulmonary fibrosis and studied their ability to secrete a chemotactic factor for monocytes. Lung T lymphocytes from all sarcoidosis patients, but not from normal subjects or patients with idiopathic pulmonary fibrosis, spontaneously secreted such a mediator. Lung T lymphocytes from patients with sarcoidosis secreted more monocyte chemotactic factor than did blood T lymphocytes from the same patients. The accumulation of monocytes in the lung in patients with pulmonary sarcoidosis may be mediated by local production of monocyte chemotactic factor by lung T lymphocytes.