In situ localization of Propionibacterium acnes DNA in lymph nodes from sarcoidosis patients by signal amplification with catalysed reporter deposition.

Sarcoidosis is a systemic granulomatous disease of unknown aetiology. Many genomes of Propionibacterium acnes and P. granulosum have been detected in lymph nodes from patients with sarcoidosis. In situ localization of propionibacterial genomes in sarcoid lymph nodes may help to establish an aetiological link between sarcoidosis and these indigenous bacteria. Formalin-fixed and paraffin-embedded biopsy samples of lymph nodes from nine patients with sarcoidosis, nine patients with tuberculosis, and nine patients with non-specific lymphadenitis as controls were examined by quantitative real-time PCR (QPCR) for P. acnes and by in situ hybridization (ISH) that used catalysed reporter deposition (CARD) for signal amplification with digoxigenin-labelled oligonucleotide probes that complemented 16S rRNA of P. acnes. The signals per 250 micro m(2) of tissue sections were counted from inside and outside the granulomas of sarcoidosis and tuberculosis and from control lymph nodes. The number of genomes by QPCR was examined for correlation with the mean signal count by ISH with CARD. In sarcoid samples, one or several signals were detected in the cytoplasm of some epithelioid cells in granulomas and of many mononuclear cells around granulomas. The mean signal counts were higher (p < 0.001) in granulomatous areas than in other areas of sarcoid lymph nodes. Even in their non-granulomatous areas, counts were higher than in granulomatous areas (p = 0.0023) and non-granulomatous areas (p < 0.001) of tuberculous lymph nodes and control lymph nodes (p = 0.0071). Correlation between the results by QPCR and ISH with CARD was significant (r = 0.86, p < 0.001). The accumulation of P. acnes genomes in and around sarcoid granulomas suggests that this indigenous bacterium may be related to the cause of granulomatous inflammation in sarcoidosis.