Background: The causes of sarcoidosis are not known. The DNA of Mycobacterium tuberculosis has been detected in some sarcoid lesions. In Japan, Propionibacterium acnes has been isolated from such lesions, but whether this indigenous bacterium is related to the disease is unclear. We used PCR to estimate the number of genomes of these bacteria in sarcoid lesions, to identify any link between sarcoidosis and these two bacterial species.
Methods: We examined formalin-fixed and paraffin-embedded sections of biopsy and surgical samples from lymph nodes of 15 patients with sarcoidosis, 15 patients with tuberculosis, and 15 patients with gastric cancer (controls). Quantitative PCR was done to amplify segments of 16 S ribosomal RNA of P. acnes and P. granulosum and of insertion sequence 6110 of M. tuberculosis. PCR products were identified and the quantities of the products were estimated in terms of the fluorescence of oligonucleotide reporter probes. The numbers of bacterial genomes in samples were estimated from standard curves of serially diluted bacterial DNA.
Findings: Genomes of M. tuberculosis were found in samples from all 15 patients with tuberculosis, from three patients with sarcoidosis, and in one control sample. Genomes of P. acnes were found in 12 of the 15 patients with sarcoidosis, in two tuberculosis patients, and three controls. The difference in the estimated number of P. acnes genomes between individuals with and without sarcoidosis was similar to that in the number of M. tuberculosis between people with and without tuberculosis. There were 5x10(5) P. acnes genomes in sarcoidosis and 3x10(6) M. tuberculosis genomes in tuberculosis, respectively, on average per microg of total DNA. The three patients with sarcoidosis but without P. acnes all had P. granulosum DNA in their biopsy samples; the number of genomes of the bacterium was 5x10(5).
Interpretation: These findings suggest that propionibacteria had resided or proliferated ectopically in the sarcoid lesions, whether there was a connection with the disease or not. Propionibacteria are a more likely cause than mycobacteria of sarcoidosis.