CD8 kinetically promotes ligand binding to the T-cell antigen receptor
CD8 kinetically promotes ligand binding to the T-cell antigen receptor
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DOI：
10.1529/biophysj.105.061671
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发表时间：
2005-09-01
影响因子：
3.4
通讯作者：
Pecht, I
中科院分区：
文献类型：
--
作者：
Gakamsky, DM;Luescher, IF;Pecht, I
在活T细胞上研究了CD 8与TCR在抗原识别中的合作机制。荧光相关测量产生的证据表明，存在两个TCR和CD 8亚群具有不同的横向扩散速率常数。独立地，两个亚群的证据来自于实验观察到的与I类MHC（pMHC）四聚体结合的同源肽和T细胞的两个不同的缔合阶段。快相速率常数（1.7 +/- 0.2 × 10（5）M-1 s（-1））与检测的细胞类型或MHC结合肽的结构无关。其值远快于可溶性pMHC与TCR的结合（（7.0 ± 0.3）× 10（3）M-1 s（-1）），接近于可溶性pMHC与CD 8的结合（（1-2）× 10（5）M-1 s（-1））。当CD 8-pMHC相互作用被CD 8特异性mAb阻断时，快速结合相消失。后一种速率常数在用甲基-β-环糊精处理细胞后减慢约10倍。这些结果表明，最有效的pMHC-细胞缔合途径对应于与共定位的CD 8-TCR亚群结合的快速四聚体，其显然位于膜筏内：反应由pMHC与CD 8缔合开始。这一明显更快的步骤显著增加了pMHC-TCR相遇的概率，从而促进了pMHC与CD 8近端TCR的结合。缓慢结合期被分配给pMHC与非共定位的CD 8-TCR亚群的结合。结合细胞毒性试验的结果，我们的数据表明，共定位，筏相关的CD 8-TCR亚群是一个能够诱导T细胞活化。
The mechanism of CD8 cooperation with the TCR in antigen recognition was studied on live T cells. Fluorescence correlation measurements yielded evidence of the presence of two TCR and CD8 subpopulations with different lateral diffusion rate constants. Independently, evidence for two subpopulations was derived from the experimentally observed two distinct association phases of cognate peptide bound to class I MHC (pMHC) tetramers and the T cells. The fast phase rate constant (( 1.7 +/- 0.2) x 10(5) M-1 s(-1)) was independent of examined cell type or MHC-bound peptides' structure. Its value was much faster than that of the association of soluble pMHC and TCR ((7.0 +/- 0.3) x 10(3) M-1 s(-1)), and close to that of the association of soluble pMHC with CD8 ((1-2) x 10(5) M-1 s(-1)). The fast binding phase disappeared when CD8-pMHC interaction was blocked by a CD8-specific mAb. The latter rate constant was slowed down similar to 10-fold after cells treatment with methyl-beta-cyclodextrin. These results suggest that the most efficient pMHC-cell association route corresponds to a fast tetramer binding to a colocalized CD8-TCR subpopulation, which apparently resides within membrane rafts: the reaction starts by pMHC association with the CD8. This markedly faster step significantly increases the probability of pMHC-TCR encounters and thereby promotes pMHC association with CD8-proximal TCR. The slow binding phase is assigned to pMHC association with a noncolocalized CD8-TCR subpopulation. Taken together with results of cytotoxicity assays, our data suggest that the colocalized, raft-associated CD8-TCR subpopulation is the one capable of inducing T-cell activation.