Immunopathogenesis of Sarcoidosis

Sarcoidosis is a multisystemic disease in which inflammatory cells gather and form nodules known as non caseating epithelioid granulomas. The most commonly affected organs are the lungs, the eyes and the skin whereas all the organs can be potentially affected. The disease can develop when genetically susceptible individuals are exposed to environmental agents with antigenic properties. These can be either exogenous agents (infections, antigenic structures) or endogenous agents produced by damaged cells. Usually the immune system is able to eliminate the granulomas over a few years but if this is not the case, a progression to fibrosis and permanent organ damage is observed. It is commonly accepted that the pathogenesis of the disease is mediated by an interplay of cells of both innate and adaptive immunity as well as by their products. Interestingly, the pathogenetic process is compartmentalized and there is an exuberant immune response occurring in the affected tissues such as increase of lymphocytes in the bronchoalveolar lavage fluid in contrast to the peripheral blood lymphocytopenia and cutaneous anergy to tuberculin and other skin tests (Daniele& Rowlands, 1976; Hunninghake,1979,1981; Siltzbach et al,1974; Winterbauer et al,1993; Yeager et al 1977). The role of the immune cells and cytokines involved in the pathogenesis of sarcoidosis will be discussed in this chapter.