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BioMed Research International
Volume 2013 (2013), Article ID 935289, 18 pages
http://dx.doi.org/10.1155/2013/935289
Review Article

Etiologic Aspect of Sarcoidosis as an Allergic Endogenous Infection Caused by Propionibacterium acnes

Department of Human Pathology, Tokyo Medical and Dental University Graduate School, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8510, Japan

Received 12 January 2013; Accepted 7 May 2013

Academic Editor: Peter A. Lambert

Copyright © 2013 Yoshinobu Eishi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Sarcoidosis is a systemic granulomatous disease of unknown etiology. Propionibacterium acnes is the only microorganism that has been isolated from sarcoid lesions. Many P. acnes have been detected in sarcoid lymph nodes using quantitative PCR and in sarcoid granulomas by in situ hybridization. P. acnes trigger 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 latent P. acnes infection in their lungs. Eradication of P. acnes by antibiotics prevents the development of granulomas in this experimental model. Although P. acnes is 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. acnes can 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 with P. acnes hypersensitivity, granulomatous inflammation is triggered by intracellular proliferation of the bacterium. Proliferating bacteria may escape granulomatous isolation, spreading to other organs. Latent P. acnes infection in systemic organs can be reactivated by another triggering event, leading to systemic sarcoidosis.