Department of Microbiology and Immunology, Stanford School of Medicine, California 94305-5323, USA.
Nature. 2010 Feb 18;463(7283):963-7. doi: 10.1038/nature08746.
The recognition of foreign antigens by T lymphocytes is essential to most adaptive immune responses. It is driven by specific T-cell antigen receptors (TCRs) binding to antigenic peptide-major histocompatibility complex (pMHC) molecules on other cells. If productive, these interactions promote the formation of an immunological synapse. Here we show that synaptic TCR-pMHC binding dynamics differ significantly from TCR-pMHC binding in solution. We used single-molecule microscopy and fluorescence resonance energy transfer (FRET) between fluorescently tagged TCRs and their cognate pMHC ligands to measure the kinetics of TCR-pMHC binding in situ. When compared with solution measurements, the dissociation of this complex was increased significantly (4-12-fold). Disruption of actin polymers reversed this effect, indicating that cytoskeletal dynamics destabilize this interaction directly or indirectly. Nevertheless, TCR affinity for pMHC was significantly elevated as the result of a large (about 100-fold) increase in the association rate, a likely consequence of complementary molecular orientation and clustering. In helper T cells, the CD4 molecule has been proposed to bind cooperatively with the TCR to the same pMHC complex. However, CD4 blockade had no effect on the synaptic TCR affinity, nor did it destabilize TCR-pMHC complexes, indicating that the TCR binds pMHC independently of CD4.
T 细胞对外源抗原的识别对于大多数适应性免疫反应至关重要。这是由特异性 T 细胞抗原受体（TCR）与其他细胞上的抗原肽-主要组织相容性复合物（pMHC）分子结合驱动的。如果这些相互作用具有生产力，则会促进免疫突触的形成。在这里，我们表明突触 TCR-pMHC 结合动力学与溶液中的 TCR-pMHC 结合有很大的不同。我们使用单分子显微镜和荧光共振能量转移（FRET）在荧光标记的 TCR 和其同源 pMHC 配体之间测量原位 TCR-pMHC 结合的动力学。与溶液测量相比，该复合物的解离显着增加（4-12 倍）。肌动蛋白聚合物的破坏逆转了这种效应，表明细胞骨架动力学直接或间接地破坏了这种相互作用。尽管如此，由于结合率显着增加（约 100 倍），TCR 对 pMHC 的亲和力显着提高，这可能是互补分子取向和聚类的结果。在辅助 T 细胞中，CD4 分子已被提议与 TCR 协同结合到相同的 pMHC 复合物上。然而，CD4 阻断对突触 TCR 亲和力没有影响，也没有破坏 TCR-pMHC 复合物，表明 TCR 独立于 CD4 结合 pMHC。
