[The mechanism and specificity of IL-1 inhibitory factor released from human alveolar macrophages]

We have previously reported the presence of interleukin 1 (IL-1) inhibitory factor in the culture supernatants of alveolar macrophages. The activity is decreased in healthy smokers and patients with interstitial lung diseases (sarcoidosis, idiopathic pulmonary fibrosis), compared with healthy non-smokers. In this study, we further examined the mechanism and specificity of IL-1 inhibitory factor. The inhibitory factor exhibited specific inhibition of augmentation by IL-1 of PHA induced murine thymocyte proliferation, whereas there was no inhibition of the augmentation by IL-2, IL-4, IL-6 or TNF. This IL-1 inhibitory factor competitively blocked the binding of IL-1 to the IL-1 receptor on PHA-stimulated murine thymocytes. These results indicate that alveolar macrophages produce a specific IL-1 inhibitory factor which functions as a IL-1 receptor antagonist.