Tani-ichi Shizue, Maruyama Koji, Kondo Nami, Nagafuku Masakazu, Kabayama Kazuya, Inokuchi Jin-ichi, Shimada Yukiko, Ohno-Iwashita Yoshiko, Yagita Hideo, Kawano Sunao, Kosugi Atsushi
Department of Immunobiology, Medical Technology and Science, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan.
Int Immunol. 2005 Jun;17(6):749-58. doi: 10.1093/intimm/dxh257. Epub 2005 Jun 20.
Lipid rafts, specialized membrane microdomains enriched in sphingolipids and cholesterol, have been shown to function as signaling platforms in T cells. Surface raft expression is known to be increased in human T cells upon activation, and this increased raft expression may account for efficient signaling capability and decreased dependency for co-stimulation in effector and/or activated T cells. However, raft-mediated signaling ability in activated T cells remains to be clarified. In this study, we analyzed the structure and function of lipid rafts in human activated T cells. We demonstrated that raft protein constituents are dramatically changed after activation along with an increase in lipid contents. T cells stimulated with anti-CD3 plus anti-CD28 antibodies showed an increase not only in surface monosialoganglioside GM1 expression but also in total amounts of raft-associated lipids such as sphingomyelin, cholesterol and glycosphingolipids. Raft proteins increased after activation include Csk, Csk-binding protein and Fyn, the molecules known to be involved in negative regulation of T cell activation. Consistent with the increase in expression of these proteins, TCR-mediated Ca(2+) response, a response dependent on raft integrity, was clearly inhibited in activated T cells. Thus, the structure and function of lipid rafts in human activated T cells seem to be quite distinct from those in naive T cells. Further, human activated T cells are relatively resistant to signaling, at least transiently, by TCR re-stimulation even though their raft expression is increased.
脂筏是富含鞘脂和胆固醇的特殊膜微区，已被证明在T细胞中作为信号平台发挥作用。已知人类T细胞激活后表面脂筏表达增加，这种增加的脂筏表达可能解释了效应和/或活化T细胞中有效的信号传导能力以及对共刺激依赖性的降低。然而，活化T细胞中脂筏介导的信号传导能力仍有待阐明。在本研究中，我们分析了人类活化T细胞中脂筏的结构和功能。我们证明，激活后脂筏蛋白成分随着脂质含量的增加而发生显著变化。用抗CD3加抗CD28抗体刺激的T细胞不仅表面单唾液酸神经节苷脂GM1表达增加，而且脂筏相关脂质如鞘磷脂、胆固醇和糖鞘脂的总量也增加。激活后增加的脂筏蛋白包括Csk、Csk结合蛋白和Fyn，这些分子已知参与T细胞激活的负调控。与这些蛋白表达的增加一致，TCR介导的Ca(2+)反应（一种依赖脂筏完整性的反应）在活化T细胞中明显受到抑制。因此，人类活化T细胞中脂筏的结构和功能似乎与未活化T细胞中的截然不同。此外，人类活化T细胞即使其脂筏表达增加，对TCR再刺激的信号传导也相对具有抗性，至少是短暂的。
