Abstract
Sarcoidosis, of unknown etiology, may result from exposure of a genetically susceptible subject to a specific environmental agent (s), possibly an infectious one, although none has been identified. Propionibacterium acnes is so far the only bacterium to be isolated from sarcoid lesions. Many genomes of P. acnes have been detected in sarcoid lymph nodes by the quantitative polymerase chain reaction. By in situ hybridization, P. acnes genomes were found in sarcoid lymph nodes in and around sarcoid granulomas. These results point to an etiological link between P. acnes and some cases of sarcoidosis. A recombinant trigger-factor protein (RP35) from P. acnes causes a cellular immune response in some patients with sarcoidosis, but not in subjects without sarcoidosis. RP35 causes pulmonary granulomas in some of the mice sensitized with the protein and adjuvant. P. acnes is the most common bacterium indigenous to the peripheral lung tissues and mediastinal lymph nodes, which may be the reason why these organs are so frequently involved in sarcoidosis. Sarcoid granulomas may be formed by a Thl immune response to one or more antigens of P. acnes indigenous to or proliferating in the affected organs in an individual with a hereditary or acquired abnormality of the immune system.
