Cambridge Institute for Medical Research, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK.
BMC Biol. 2011 Jun 28;9:45. doi: 10.1186/1741-7007-9-45.
Cytolytic cells of the immune system destroy pathogen-infected cells by polarised exocytosis of secretory lysosomes containing the pore-forming protein perforin. Precise delivery of this lethal hit is essential to ensuring that only the target cell is destroyed. In cytotoxic T lymphocytes (CTLs), this is accomplished by an unusual movement of the centrosome to contact the plasma membrane at the centre of the immunological synapse formed between killer and target cells. Secretory lysosomes are directed towards the centrosome along microtubules and delivered precisely to the point of target cell recognition within the immunological synapse, identified by the centrosome. We asked whether this mechanism of directing secretory lysosome release is unique to CTL or whether natural killer (NK) and invariant NKT (iNKT) cytolytic cells of the innate immune system use a similar mechanism to focus perforin-bearing lysosome release.
NK cells were conjugated with B-cell targets lacking major histocompatibility complex class I 721.221 cells, and iNKT cells were conjugated with glycolipid-pulsed CD1-bearing targets, then prepared for thin-section electron microscopy. High-resolution electron micrographs of the immunological synapse formed between NK and iNKT cytolytic cells with their targets revealed that in both NK and iNKT cells, the centrioles could be found associated (or 'docked') with the plasma membrane within the immunological synapse. Secretory clefts were visible within the synapses formed by both NK and iNKT cells, and secretory lysosomes were polarised along microtubules leading towards the docked centrosome. The Golgi apparatus and recycling endosomes were also polarised towards the centrosome at the plasma membrane within the synapse.
These results reveal that, like CTLs of the adaptive immune system, the centrosomes of NK and iNKT cells (cytolytic cells of the innate immune system) direct secretory lysosomes to the immunological synapse. Morphologically, the overall structure of the immunological synapses formed by NK and iNKT cells are very similar to those formed by CTLs, with both exocytic and endocytic organelles polarised towards the centrosome at the plasma membrane, which forms a focal point for exocytosis and endocytosis within the immunological synapse. We conclude that centrosomal polarisation provides a rapid, responsive and precise mechanism for secretory lysosome delivery to the immunological synapse in CTLs, NK cells and iNKT cells.
免疫系统的溶细胞毒性细胞通过极化细胞外泌作用破坏含有成孔蛋白穿孔素的分泌溶酶体来杀死病原体感染的细胞。精确传递这种致命打击对于确保仅破坏靶细胞至关重要。在细胞毒性 T 淋巴细胞 (CTL) 中，这是通过中心体向杀伤细胞和靶细胞之间形成的免疫突触中心的质膜的异常运动来实现的。分泌溶酶体沿着微管向中心体移动，并沿着微管精确递送到免疫突触中靶细胞识别的位置，该位置由中心体识别。我们想知道这种分泌溶酶体释放的导向机制是否仅存在于 CTL 中，或者天然杀伤 (NK) 和不变自然杀伤 T (iNKT) 细胞等先天免疫系统的溶细胞毒性细胞是否使用类似的机制来集中穿孔素携带的溶酶体释放。
将 NK 细胞与缺乏主要组织相容性复合体 I 类的 B 细胞靶标 721.221 细胞共轭，将 iNKT 细胞与糖脂脉冲 CD1 结合的靶标共轭，然后准备进行薄切片电子显微镜检查。与靶细胞形成的 NK 和 iNKT 细胞免疫突触的高分辨率电子显微镜图显示，在 NK 和 iNKT 细胞中，中心粒都可以在免疫突触内与质膜相关联（或“对接”）。在由 NK 和 iNKT 细胞形成的突触中都可以看到分泌裂隙，并且分泌溶酶体沿着微管极化，朝向对接的中心粒。高尔基氏体和再循环内体也在突触内的质膜处朝向中心粒极化。
这些结果表明，与适应性免疫系统的 CTL 一样，NK 和 iNKT 细胞（先天免疫系统的溶细胞毒性细胞）的中心体将分泌溶酶体导向免疫突触。从形态上看，NK 和 iNKT 细胞形成的免疫突触的总体结构与 CTL 形成的免疫突触非常相似，外向和内吞细胞器都向质膜处的中心体极化，这形成了免疫突触内胞吐和胞吞的焦点。我们得出结论，中心体极化提供了一种快速、响应和精确的机制，用于将分泌溶酶体递送到 CTL、NK 细胞和 iNKT 细胞的免疫突触中。
