Effect of IL-6 on alveolar fibroblast proliferation in interstitial lung diseases

Alveolar macrophage-fibroblast interaction may be involved in the pathogenesis of interstitial lung diseases (ILD). Herein, we compared IL-6 secretion hom alveolar macrophages (AM) and alveolar fibroblasts (AFb) recovered from patients with sarcoidosis (SA) and with diffuse interstitial fibrosis (DIF). Moreover, we evaluated the effect of IL-6 on the in vitro AFb proliferation in both diseases. AM and AFb from SA patients showed increased spontaneous secretion of IL-6 compared with cells from DH subjects. Tumor necrosis factor-alpha (TNF alpha) and interleukin-1 (IL-1) enhanced IL-6 secretion and IL-6 mRNA transcription in AFb of SA patients. Addition of anti-IL-g MoAbs increased AFb proliferation capacity in SA, but suppressed it in DIF. These results show that only SA AM and AFb secrete high levels of IL-6 which have suppressive effect on AFb proliferation. This may indicate a potential role of IL-6 in the fibrogenesis of ILD. (C) 1996 Academic Press, Inc.