Etiologic Aspect of Sarcoidosis as an Allergic Endogenous Infection Caused byPropionibacterium acnes

Abstract

Sarcoidosis is a systemic granulomatous disease of unknown etiology.Propionibacterium acnesis the only microorganism that has been isolated from sarcoid lesions. ManyP. acneshave been detected in sarcoid lymph nodes using quantitative PCR and in sarcoid granulomas byin situhybridization.P. acnestrigger factor protein causes a cellular immune response only in sarcoid patients and induces pulmonary granulomas in mice sensitized with the protein and adjuvant, but only those with latentP. acnesinfection in their lungs. Eradication ofP. acnesby antibiotics prevents the development of granulomas in this experimental model. AlthoughP. acnesis the most common commensal bacterium in the lungs and lymph nodes,P. acnes-specific antibody detected the bacterium within sarcoid granulomas of these organs.P. acnescan cause latent infection in the lung and lymph node and persist in a cell-wall-deficient form. The dormant form is activated endogenously under certain conditions and proliferates at the site of latent infection. In patients withP. acneshypersensitivity, granulomatous inflammation is triggered by intracellular proliferation of the bacterium. Proliferating bacteria may escape granulomatous isolation, spreading to other organs. LatentP. acnesinfection in systemic organs can be reactivated by another triggering event, leading to systemic sarcoidosis.