BACKGROUND: Interactions between mononuclear cells, vascular endothelium, fibroblasts, and cytokines during the inflammatory reaction within a granuloma have the potential to contribute to the progression to fibrosis. METHODS: Biopsy specimens of six tuberculous and eight sarcoidosis skin lesions were examined by immunohistochemistry to seek evidence for the presence of inflammatory and fibrotic reactions in human granulomatous disease. Additionally, to understand how a T cell mediated delayed type hypersensitivity reaction--a component of chronic granulomatous inflammation--could progress to fibrosis, the human in vivo model of the cutaneous tuberculin Heaf reaction to purified protein derivative (PPD) was studied in a group of 48 subjects. RESULTS: Granulomas from tuberculous and sarcoidosis skin biopsy specimens were seen to contain cells with marked staining by antibodies to fibronectin, transforming growth factor beta (pan TGF-beta), and type 1 procollagen (PCP-1). Accentuated staining of extracellular matrix was seen both in the granulomas and in the peri-granulomatous regions. Less prominent staining was observed using antibodies against interleukin 1 beta (IL-1 beta) and alpha-smooth muscle actin (alpha-SMA). Biopsies of Heaf reactions revealed cells staining for IL-1 beta, tumour necrosis factor alpha (TNF-alpha), platelet derived growth factor B (PDGF-B), and fibronectin which were detected as early as day 1 and persisted throughout the 14 day study period. Cells staining for PCP-1 increased to greatest abundance at day 14. All these cytokines were present in low abundance in biopsy specimens from sites inoculated with saline only. CONCLUSIONS: Evidence is provided that granulomas in tuberculosis and sarcoidosis behave as active centres of fibrogenesis. Using the Heaf model, the temporal relationship between the early appearance of cytokines and the later increase in the collagen precursor PCP-1 linked the immune mediated chronic inflammatory response with subsequent fibrosis and suggested that the tuberculin Heaf reaction will serve as a model for studying the early events of granuloma formation in patients with tuberculosis and sarcoidosis.
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