Haddad E K, Wu X, Hammer J A, Henkart P A
Experimental Immunology Branch, National Cancer Institute;, and.
J Cell Biol. 2001 Feb 19;152(4):835-42. doi: 10.1083/jcb.152.4.835.
Because mutations in Rab27a have been linked to immune defects in humans, we have examined cytotoxic lymphocyte function in ashen mice, which contain a splicing mutation in Rab27a. Ashen cytotoxic T lymphocytes (CTLs) showed a >90% reduction in lytic activity on Fas-negative target cells compared with control C3H CTLs, and ashen natural killer cell activity was likewise diminished. Although their granule-mediated cytotoxicity pathway is profoundly defective, ashen CTLs displayed a normal FasL-Fas cytotoxicity pathway. The CD4/8 phenotype of ashen T cells and their proliferative responses were similar to controls. Ashen CTLs had normal levels of perforin and granzymes A and B and normal-appearing perforin-positive granules, which polarized upon interaction of the CTLs with anti-CD3-coated beads. However, rapid anti-CD3-induced granule secretion was drastically defective in both CD8(+) and CD4(+) T cells from ashen mice. This defect in exocytosis was not observed in the constitutive pathway, as T cell receptor-stimulated interferon-gamma secretion was normal. Based on these results and our demonstration that Rab27a colocalizes with granzyme B-positive granules and is undetectable in ashen CTLs, we conclude that Rab27a is required for a late step in granule exocytosis, compatible with current models of Rab protein function in vesicle docking and fusion.
由于Rab27a突变与人类免疫缺陷有关，我们检测了灰鼠的细胞毒性淋巴细胞功能，这些灰鼠的Rab27a存在剪接突变。与对照C3H细胞毒性T淋巴细胞（CTL）相比，灰鼠CTL对Fas阴性靶细胞的裂解活性降低了90%以上，且灰鼠自然杀伤细胞活性同样降低。尽管其颗粒介导的细胞毒性途径存在严重缺陷，但灰鼠CTL显示出正常的FasL-Fas细胞毒性途径。灰鼠T细胞的CD4/8表型及其增殖反应与对照相似。灰鼠CTL的穿孔素、颗粒酶A和B水平正常，穿孔素阳性颗粒外观正常，在CTL与抗CD3包被的珠子相互作用时会极化。然而，来自灰鼠的CD8(+)和CD4(+) T细胞中，快速抗CD3诱导的颗粒分泌存在严重缺陷。在组成性途径中未观察到这种胞吐缺陷，因为T细胞受体刺激的γ干扰素分泌正常。基于这些结果以及我们所证明的Rab27a与颗粒酶B阳性颗粒共定位且在灰鼠CTL中无法检测到，我们得出结论，Rab27a是颗粒胞吐后期步骤所必需的，这与当前Rab蛋白在囊泡对接和融合中的功能模型相符。
