T cells exhibit remarkable sensitivity and selectivity in detecting and responding to agonist peptides (p) bound to MHC molecules in a sea of self pMHC molecules. Despite much work, understanding of the underlying mechanisms of distinguishing such ligands remains incomplete. Here, we quantify T cell discriminatory capacity using channel capacity, a direct measure of the signaling network’s ability to discriminate between antigen-presenting cells (APCs) displaying either self ligands or a mixture of self and agonist ligands. This metric shows how differences in information content between these two types of peptidomes are decoded by the topology and rates of kinetic proofreading signaling steps inside T cells. Using channel capacity, we constructed numerically substantiated hypotheses to explain the discriminatory role of a recently identified slow LAT Y132 phosphorylation step. Our results revealed that in addition to the number and kinetics of sequential signaling steps, a key determinant of discriminatory capability is spatial localization of a minimum number of these steps to the engaged TCR. Biochemical and imaging experiments support these findings. Our results also reveal the discriminatory role of early negative feedback and necessary amplification conferred by late positive feedback.

T细胞在检测和响应自身pMHC分子海中与MHC分子结合的激动剂肽（p）方面表现出卓越的灵敏度和选择性。尽管做了很多工作，对区分这些配体的潜在机制的理解仍然不完整。在这里，我们使用通道容量来量化T细胞的区分能力，通道容量是信号网络区分抗原呈递细胞（APC）的能力的直接度量，该抗原呈递细胞显示自身配体或自身与激动剂配体的混合物。该度量表明如何通过T细胞内部的拓扑结构和动态校对信号转导步骤的速率来解码这两种肽基之间的信息含量差异。利用频道容量，我们构建了数字化的假设来解释最近确定的缓慢LAT Y132磷酸化步骤的歧视性作用。我们的研究结果表明，除了顺序信号传导步骤的数量和动力学外，判别能力的关键决定因素是这些步骤中最少数量的空间定位于参与的TCR。生化和成像实验支持了这些发现。我们的研究结果还揭示了早期负反馈的歧视作用以及后期正反馈赋予的必要放大作用。生化和成像实验支持了这些发现。我们的研究结果还揭示了早期负反馈的歧视作用以及后期正反馈赋予的必要放大作用。生化和成像实验支持了这些发现。我们的研究结果还揭示了早期负反馈的歧视作用以及后期正反馈赋予的必要放大作用。