Propionibacterium acnes (P. acnes) was isolated in high rates and in high concentrations from lymph nodes in patients with sarcoidosis. However, the precise mechanism of granuloma formation and immunomodulation by P. acnes has not been elucidated yet. In patients with sarcoidosis, it was found that the high levels of interleukin-2 released from alveolar lymphocytes as well as interleukin-1, tumor necrosis factor and interleukin-6 released from alveolar macrophages were stimulated by P. acnes. These cytokines (mainly IL-2), released by P. acnes in large quantities, play a major role in the compartmentalization of the T-cell population in the lung and lead to the formation of alveolitis and granuloma in the lung parenchyma of patients with sarcoidosis.