Physiology of granulomas

: Granulomas are a local formation of specific cells including macrophages and lymphocytes revealing a chronic inflammatory reaction against infection, often due to intracellular agents. Granulomas can be composed of macrophages (foreign body reaction), epithelioid cells (immune granulomas of sarcoidosis, tuberculosis), or Langerhans' cells (histiocytosis X). In immune granulomas, the epithelioid cells derived from activated macrophages are found at the centre of the granuloma associated with CD4+ T-lymphocytes, while the periphery is mainly populated with CD8+ T-lymphocytes. Granulomas are not static formations, the rate of cell turnover is high. Different cytokines have been identified as mediators involved in the formation and maintenance of these granulomas: IL2, interferon gamma, TNF alpha, 1,25(OH)2D3, IL1. Major questions, especially concerning antigens involved in granulomatous reactions, remain to be answered for a better understanding of these events.