Th1 and Th17 immune responses to viable Propionibacterium acnes in patients with sarcoidosis

Propionibacterium acnes and Mycobacterium tuberculosis have emerged as probable candidates responsible for sarcoidosis. This study was conducted to investigate the Th1/Th17 responses elicited by these pathogens in sarcoidosis and to clarify the causative role of these pathogens.

Peripheral blood mononuclear cells (PBMCs) obtained from patients with sarcoidosis and from healthy volunteers were, respectively, co-cultured with viable P. acnes, with Bacille de Calmette et Guérin (BCG) as a viable M. tuberculosis complex, and with the early secretory antigenic target (ESAT)-6. Th1 cytokine production was measured using RT-PCR and enzyme-linked immunospot (ELISPOT) assays, and interleukin (IL)-17 mRNA expression was measured by RT-PCR.

IL-2 secretion from PBMCs after stimulation with P. acnes was significantly higher in patients with sarcoidosis than in the controls. Similarly, IL-2 and IL-12 mRNA expression after stimulation with P. acnes was significantly higher in PBMCs from patients with sarcoidosis than in PBMCs from controls. In contrast, IL-17 mRNA expression was significantly lower in PBMCs from patients with sarcoidosis than in PBMCs from controls. No significant differences between the groups were observed in the responses to stimulation with BCG or ESAT-6.

Sarcoidosis may arise from an imbalance of Th1/Th17 immune responses against viable P. acnes, but not M. tuberculosis complex.