Raychaudhuri Kumarkrishna, Rangu Rohita, Ma Alison, Alvinez Neriah, Tran Andy D, Pallikkuth Sandeep, McIntire Katherine M, Garvey Joseph A, Yi Jason, Samelson Lawrence E
bioRxiv. 2024 Nov 22:2024.06.27.601067. doi: 10.1101/2024.06.27.601067.
T cell activation requires T cell receptor (TCR) engagement, which initiates a series of proximal events including tyrosine phosphorylation of the CD3 and TCRζ chains, recruitment, and activation of the protein tyrosine kinases Lck and ZAP70, followed by recruitment of adapter and signaling proteins. CD28 co-stimulation is also required to generate a functional immune response. Currently we lack a full understanding of the molecular mechanism of CD28 activation. TCR microclusters (MC) are submicron-sized molecular condensates and basic signaling units that form immediately after TCR ligation. Our results show that CD28 co-stimulation specifically accelerated recruitment of ZAP70 to the TCRζ chain in MCs and increased ZAP70 activation. This CD28-mediated acceleration of ZAP70 recruitment was driven by enhanced Lck recruitment to the MCs. A greater spatial separation between active and inactive species of Lck was also observed in the MCs as a consequence of CD28 co-stimulation. These results suggest that CD28 co-stimulation may lower the TCR activation threshold by enhancing the activated form of Lck in the TCR MCs.
T细胞活化需要T细胞受体（TCR）的结合，这会引发一系列近端事件，包括CD3和TCRζ链的酪氨酸磷酸化、蛋白酪氨酸激酶Lck和ZAP70的募集与激活，随后募集衔接蛋白和信号蛋白。CD28共刺激对于产生功能性免疫反应也是必需的。目前我们对CD28激活的分子机制还缺乏全面的了解。TCR微簇（MC）是亚微米大小的分子凝聚物和基本信号单元，在TCR连接后立即形成。我们的结果表明，CD28共刺激特异性地加速了ZAP70向MC中TCRζ链的募集，并增强了ZAP70的激活。这种由CD28介导的ZAP70募集加速是由Lck向MCs的募集增强所驱动的。由于CD28共刺激，在MCs中还观察到Lck的活性和非活性形式之间有更大的空间分离。这些结果表明，CD28共刺激可能通过增强TCR MCs中Lck的激活形式来降低TCR激活阈值。
