Inflammatory reaction of sarcoidosis. The initial response of sarcoidosis is mediated by CD4 and APCs which release a large number of cytokines. Over time, the granuloma can either resolve or go on to form fibrosis. Fibrosis is associated with TNF, IL-8 and ET-1. Ag, antigen; APC, antigen-presenting cell; ET, endothelin; HLA, human leucocyte antigen; IFN, interferon; IL, interleukin; TNF, tumour necrosis factor. Reproduced with permission from Baughman et al.: Tumour necrosis factor in sarcoidosis and its potential for targeted therapy. Biodrugs 2003, 17(6): 425–431. © Wolters Kluwer Health .