Human alveolar macrophage subpopulations isolated on discontinuous albumin gradients: Functional data in normals and sarcoid patients

Cells recovered by bronchoalveolar lavage from seven normals and seven sarcoid patients were centrifuged on discontinuous bovine albumin (BSA) gradients to study alveolar macrophage (AM) heterogeneity. The gradient was made with nine BSA concentrations from 8 to 30%. After centrifugation, the cells were recovered from the nine interfaces, named a to i. The majority of the AM was recovered from layers b to g. Regulatory activity of AM subpopulations was tested on mitogen-induced blood mononuclear cells (BMC) proliferation: (1) autologous BMC were cocultured with AM from the different layers; (2) 16-h culture supernatants of AM subfractions were added to allogeneic BMC cultures from normal donors. In the autologous assay, AM from the middle layers exhibited a stimulatory activity in normals and even more in sarcoid patients, while AM from the upper layers showed an inhibitory activity in normals but a stimulatory activity in sarcoid patients. In the allogeneic assay, a suppressive effect was found in culture supernatants from normal AM. On the other hand, in sarcoid patients, culture supernatants were less inhibiting, but the inhibitory activity was in both cases maximal in b. These results confirm functional heterogeneity of human AM, and demonstrate that the AM subpopulations differ between normals and sarcoid patients.