Epithelioid cell granulomatosis of the lung: new insights and concepts.

Our knowledge on epithelioid cell granulomatosis of the lung has been extended in recent years. New entities have been added, like zirconiosis; others like tuberculosis, mycobacteriosis and sarcoidosis have gained new interest, because molecular techniques allowed new insight into their pathogenesis and a more rapid and species-specific diagnosis. Experimental work in addition has added a lot of information about the network of cytokines and other inflammatory mediators responsible for granuloma formation. However, our knowledge of this network is still incomplete. Three types of agents are now known to cause epithelioid cell granulomas: infectious organisms (bacteria and fungi), products of plants and animals (pollen, sporangia, proteins), and metallic compounds. In addition, there is still a group of epithelioid cell granulomatoses with unknown etiology. Sarcoidosis, one of these granulomatoses has recently elicited an old controversy; by molecular techniques atypical Mycobacteria and Corynebacterium acne have been identified in sarcoid granulomas and a link to the etiology of sarcoidosis has been proposed. Whether these bacteria induce some cases of sarcoidosis by an allergic mechanism, has still to be proven.