Galectin-3在T細胞活化與凋亡之研究

Abstract

Galectin-3，為分子量31 kDa的蛋白質，是屬於beta-galectose-binding lectin家族的一員，能正向與負向地調節T細胞和巨噬細胞的免疫功能。Galectin-3主要分布於細胞質內，然而近期研究也在細胞核、細胞表面以及細胞外間質偵測到Galectin-3的表現，暗示此分子為多功能性蛋白質。目前有越來越多的研究證據指出Galectin-3會參與調節T細胞免疫功能和細胞凋亡。Galectin-3能正向和負向地調節T細胞反應，但是Galectin-3在T細胞活化和凋亡方面的角色仍舊不是很清楚。為了要研究Galectin-3對T細胞的作用，首先，我們分離人類T細胞，進一步去研究Galectin-3對T細胞活化的影響。我們證實當T細胞藉由anti-CD3抗體活化之後其Galectin-3的表現量會提高，而此增加表現的趨勢在核酸和蛋白質階層下都能觀察到。利用anti-CD3抗體引發T細胞活化的同時加入Galectin-3，能造成T細胞增生並引起細胞激素IFNγ和IL-4的分泌。自Galectin-3基因敲毀小鼠所分離出的splenocytes對anti-CD3抗體所產生的活化反應較差，而此缺失能藉由外加Galectin-3所修復。以上實驗指出Galectin-3具有調節T細胞活化之功能。Galectin-3除了能增強T細胞活化之外，外源性的Galectin-3也能引發細胞凋亡。為了進一步去探討Galectin-3在人類T細胞所引發的細胞凋亡，我們分離人類T細胞，進而去研究在不同的活化狀態之下以及不同的T細胞亞群之間對Galectin-3所引發的細胞凋亡的反應。我們的結果發現，活化狀態下的T細胞對Galectin-3所引發的細胞凋亡較靜止狀態下的T細胞表現比較高的抗性，暗指T細胞對Galectin-3所引發的細胞凋亡受活化狀態所調控。另外我們也證明CD8 T細胞比CD4 T細胞對Galectin-3所引發的細胞凋亡表現比較高的敏感性，而在CD45RA和CD45RO T細胞亞群之間沒有顯著差異，暗示naïve和memory T細胞對Galectin-3所引發的細胞凋亡感受性沒有差異。而Galectin-3所引發的細胞凋亡能藉由外加caspase 抑制劑所抑制。綜合實驗結果顯示Galectin-3的確在調節T細胞活化跟凋亡方面有重要的角色。

Galectin-3, a 31 kDa protein, belonging to the member of a growing family of beta – galactoside - binding lectin, positively and negatively regulates T cell immunity and macrophage function. Although Galectin-3 is predominantly located in the cytoplasm, it has also been detected in the nucleus, on the cell surface or in the extracellular environment, suggesting a multi-functionality of this molecule. There is growing evidence showing the involvement of galectin-3 in the regulation of T cell immune response and apoptosis. Galetin-3 can positively and negatively regulate T cell response. Role of galectin-3 in T cell activation and apoptosis is still not clear. In order to investigate the effects of galectin-3 in T cells, we isolated human T cells to study T cell activation in vitro. We demonstrated that the expression of galectin-3 is upregulated in primary human T cells when cells activated with anti-CD3 mAb in both real-time PCR and intracellular galectin-3 staining. The exposure of exogenous galectin-3 to primary human T cells enhanced proliferation response to immobilized anti-CD3. We further demonstrated that exogenous galectin-3 induced IFN-γ production during T cell activation. The splenocytes isolated from galectin-3 deficient mice impaired proliferation response to anti-CD3 and this defect can be restored by adding recombinant galectin-3, indicating that galectin-3 may play a role in T cell activation. In addition to induce T cell activation, exogenous galectin-3 is also able to induce apoptosis in resting T cells. For investigating role of galectin-3-induced apoptosis in human T cells, we isolated primary human T cells and study the response to exogenous galectin-3 in different activation states and T cell subsets. The results revealed that activated T cells were more resistant to galecin-3-induced apoptosis than resting T cells indicating that galectin-3-induced apoptosis is under regulation, depending on T cell activation states. We also demonstrated that CD8 T cells were more sensitive to galectin-3-induced apoptosis than CD4 T cells and there was no significant difference between CD45RO and CD45RA T cell subsets in galectin-3-induced cell apoptosis indicating that no significant difference between naïve and primary T cell subsets. Galectin-3-induced apoptosis could be inhibited by caspase inhibitors. In conclusion, these results suggest that galectin-3 may play an important role in T cell activation and apoptosis.