Stimulated human alveolar macrophages secrete interferon.

Alveolar macrophages were isolated by bronchoalveolar lavage from normal subjects to determine whether these cells can be activated to produce interferon. Macrophages were incubated for 24 h, and the supernatants were assayed for interferon using a plaque reduction assay (vesicular stomatitis virus and human amnion cells). The macrophages did not spontaneously release detectable amounts of interferon, but macrophages stimulated with either mitogens or classic inducers did release antiviral activity (titer range, 32 to 962 units/ml). Interferon activity was detectable after 4h incubation. In general, macrophages that responded to one stimulating agent responded to all tested, and concanavalin A (25 micrograms/ml) produced the highest titer (mean, 335 units/ml). Peripheral blood lymphocytes at cell densities (1 X 10(5)/ml) comparable to that present in the macrophage suspension did not produce detectable amounts of interferon using identical culture and assay conditions. There was no difference between monocytes and alveolar macrophages in the amounts of interferon produced after 24 h, and there was also no apparent effect of cigarette smoking on the production of interferon by alveolar macrophages. Alveolar macrophages appeared to release gamma-interferon with mitogen stimulation (Con A) and alpha-interferon with UV-inactivated influenza A virus stimulation. We conclude that stimulated human alveolar macrophages can secrete both alpha- and gamma-interferon. This capacity for interferon production by alveolar macrophages may have important implications for antiviral defenses in the lung and may modulate certain pulmonary inflammatory and immune processes.