Immunosuppressive Effects of Bryoria sp. (Lichen-Forming Fungus) Extracts via Inhibition of CD8+ T-Cell Proliferation and IL-2 Production in CD4+ T Cells.

Lichen-forming fungi are known to have various biological activities, such as antioxidant, antimicrobial, antitumor, antiviral, anti-inflammation, and anti proliferative effects. However, the immunosuppressive effects of Bryoria sp. extract (BSE) have not previously been investigated. In this study, the inhibitory activity of BSE on the proliferation of CD8+ T cells and the mixed lymphocytes reaction (MLR) was evaluated in vitro. BSE was non-toxic in spleen cells and suppressed the growth of splenocytes induced by anti-CD3. The suppressed cell population in spleen cells consisted of CD8+ T cells and their proliferation was inhibited by the treatment with BSE. This extract significantly suppressed the IL-2 associated with T cell growth and IFN-γ as the CD8+ T cell marker. Furthermore, BSE reduced the expression of the IL-2 receptor alpha chain (IL-2Rα) on CD8+ T cells and CD86 on dendritic cells by acting as antigen-presenting cells. Finally, the MLR produced by the co-culture of C57BL/6 and MMC-treated BALB/c was suppressed by BSE. IL-2, IFN-γ, and CD69 on CD8+ T cells in MLR condition were inhibited by BSE. These results indicate that BSE inhibits the MLR via the suppression of IL-2Rα expression in CD8+ T cells. BSE has the potential to be developed as an anti-immunosuppression agent for organ transplants.