台灣紫芝多醣體對淋巴細胞免疫調節之研究

Abstract

台灣紫芝 (Ganoderma formosanum) 為台灣本島特有靈芝品種，目前對於紫芝 的相關研究仍相當稀少且僅有一篇文獻研究台灣紫芝子實體熱水萃取物，其清除 自由基能力及護肝效果之評估。真菌細胞壁主成分中的多醣體主要由 β-glucans 構 成，已有許多研究指出 β-glucans 可以刺激免疫細胞。因此在本篇研究中，將探討 台灣紫芝多醣體 F2 是否能夠對脾臟淋巴細胞有免疫調節的能力。首先，我們發 現 F2 能刺激脾臟淋巴細胞的增生，且此活性不會因多黴素 (polymyxin B) 的處理 而受到影響，因此排除了樣品可能受到脂多醣 (LPS) 的汙染的機會。另外經蛋白 質水解酶 (protease K) 處理過之 F2 也仍保留刺激活性，顯示 F2 刺激脾臟淋巴細 胞的能力的確是來自於多醣體 (polysaccharides) 而非來自蛋白質。雖然實驗發 現 F2 無法直接刺激 CD4 T 淋巴球增生，但在 F2 刺激脾臟淋巴細胞時，可間接使 其中的 CD4 T 淋巴球產生 IFN-γ 而走向 Th1 免疫反應。除此之外，經由實驗發現 F2 可直接刺激 B 淋巴球的增生及增加早期活化抗原(CD69 及 CD86) 的表現及 M 型 免疫球蛋白 (IgM) 的產生，這些結果顯示出 F2 可誘導 B 淋巴球分化成 IgM 分泌 型的 B 淋巴球。最後實驗發現此 F2 所誘導 B 淋巴球產生 IgM 是透過 MAPK, NF-κB 及 Syk 路徑，但透過何種受體 (receptor) 及詳細的機制仍需更進一步的實驗證 實。

Ganoderma formosanum is a native species of Ganoderma sp. in Taiwan. Until now, there has been only very few studies on this Ganoderma strain. The polysaccharides of fungal cell wall, which mainly consist of β-glucans moieties, have been reported to serve as microbial ligands that can stimulate pattern-recognition receptors on immune cells. A major polysaccharide fraction, F2, was purified from the submerged culture of G. formosanum, and in this study, we examined the immunomodulatory activity of F2 in mouse splenic lymphocytes. We found that F2 could stimulate the proliferation of splenocytes. Polymyxin B treatment did not significantly affect the activity of F2, excluding the possibility LPS contamination in our samples. Protease K-treated F2 still retained the stimulatory function, indicating that it was the polysaccharides, but not any protein component, that contributed to the stimulation of splenocytes. F2 could not stimulate splenic CD4 T lymphocyte proliferation directly; however it stimulated the production of IFN-γ, a Th1 cytokine, from CD4 T lymphocytes in the splenocyte culture. In contrast, F2 stimulated splenic B lymphocyte proliferation directly, and F2 stimulation increased the expression of early activation antigen (CD69 and CD86) and induced IgM production. Finally, our results indicated that MAPK (ERK, p38, JNK), NF-κB and Syk signaling pathways are involved in F2-stimulated IgM production in B lymphocytes. Further studies will be done to investigate the detailed mechanisms including specific receptor(s) on B lymphocytes that are activated by the polysaccharides of Ganoderma formosanum.