The affinity of T-cell receptors (TCRs) for major histocompatibility complex molecules (MHCs) presenting cognate antigens likely determines whether T cells initiate immune responses, or not. There exist few measurements of two-dimensional (2D) TCR–MHC interactions, and the effect of auxiliary proteins on binding is unexplored. Here, Jurkat T-cells expressing the MHC molecule HLA-DQ8-glia-α1 and the ligand of an adhesion protein (rat CD2) were allowed to bind supported lipid bilayers (SLBs) presenting fluorescently labelled L3-12 TCR and rat CD2, allowing measurements of binding unconfounded by cell signaling effects or co-receptor binding. The 2D K_d for L3-12 TCR binding to HLA-DQ8-glia-α1, of 14±5 molecules/μm² (mean±s.d.), was only marginally influenced by including CD2 up to ~200 bound molecules/μm² but higher CD2 densities reduced the affinity up to 1.9-fold. Cell–SLB contact size increased steadily with ligand density without affecting binding for contacts at up to ~20% of total cell area, but beyond this lamellipodia appeared, giving an apparent increase in bound receptors of up to 50%. Our findings show how parameters other than the specific protein–protein interaction can influence binding behavior at cell–cell contacts.

T 细胞受体 (TCR) 对呈递同源抗原的主要组织相容性复合体分子 (MHC) 的亲和力可能决定 T 细胞是否启动免疫反应。二维 (2D) TCR-MHC 相互作用的测量很少，并且辅助蛋白对结合的影响尚未探索。在这里，表达 MHC 分子 HLA-DQ8-glia-α1 和粘附蛋白配体（大鼠 CD2）的 Jurkat T 细胞被允许结合呈现荧光标记的 L3-12 TCR 和大鼠 CD2 的支持脂质双层（SLB），从而允许结合测量不受细胞信号传导效应或共受体结合的干扰。L3-12 TCR 与 HLA-DQ8-glia-α1 结合的2D K _{d为 14±5 个分子/μm} ² (平均值±标准差)，仅受到包含高达约 200 个结合分子/μm ²的 CD2 的轻微影响，但较高的 CD2 密度使亲和力降低达 1.9 倍。细胞-SLB接触尺寸随着配体密度的增加而稳定增加，而不影响总细胞面积约20%的接触结合，但超出这个片状伪足出现，使结合受体明显增加高达50%。我们的研究结果表明，除了特定的蛋白质-蛋白质相互作用之外的参数如何影响细胞-细胞接触的结合行为。