[Cytokines and pulmonary fibroses]

Pulmonary fibrosis corresponds to an accumulation of collagens and other proteins of the extracellular matrix in the interstitium and alveoli. Biochemical and cellular mechanisms of pulmonary fibrogenesis remain poorly understood. The cells of the alveolitis (macrophages, lymphocytes and neutrophils) play a key role in producing the factors which regulate the proliferation, chemotactism and secretory activity of the fibroblasts. Amongst these factors the cytokines (interleukins, interferons and growth factors) play a definite but very complex role. Certain cytokines stimulate in vitro the attraction and activation of cells of the alveolitis, as well as the multiplication, migration and secretory activity of fibroblasts. The following cytokines are involved: tumour necrosis factor alpha: (TNF alpha), interleukin 1 (IL-1), interleukin 6 (IL-6) interleukin 8 (IL-8) transforming growth factor beta (TGF beta), platelet derived growth factor (PDGF), insulin like growth factor 1 (IGF-1), fibronectin, monocyte chemotactic protein 1: (MCP-1). Other cytokines, principally the interferons (of alpha, beta or gamma type: IFN alpha, IFN beta, IFN gamma) inhibit in vitro and in vivo the proliferation and the production of collagen by fibroblasts. During the course of human pulmonary fibrosis or in experimental situations, the majority of the cytokines mentioned above are produced in excess in the lung. Without doubt they play an important role in the pathogenesis of fibrosis, even if it is not yet very well known how they interact and contribute in vitro to the process of fibrogenesis. Certain cytokines potentially regulating in the fibrosis are yet to be identified. In the future the use of cytokines and of their inhibitors will perhaps provide new therapies in pulmonary fibrosis.