Institut Pasteur, Dynamics of Immune Responses Unit, Paris, France.
Blood. 2012 Nov 8;120(19):3945-8. doi: 10.1182/blood-2012-01-408260. Epub 2012 Sep 20.
T-cell activation in lymph nodes relies on encounters with antigen (Ag)-bearing dendritic cells (DCs) but the number of DCs required to initiate an immune response is unknown. Here we have used a combination of flow cytometry, 2-photon imaging, and computational modeling to quantify the probability of T cell-DC encounters. We calculated that the chance for a T cell residing 24 hours in a murine popliteal lymph nodes to interact with a DC was 8%, 58%, and 99% in the presence of 10, 100, and 1000 Ag-bearing DCs, respectively. Our results reveal the existence of a threshold in DC numbers below which T-cell responses fail to be elicited for probabilistic reasons. In mice and probably humans, we estimate that a minimum of 85 DCs are required to initiate a T-cell response when starting from precursor frequency of 10(-6). Our results have implications for the rational design of DC-based vaccines.
T 细胞在淋巴结中的激活依赖于与携带抗原（Ag）的树突状细胞（DC）的相遇，但启动免疫反应所需的 DC 数量尚不清楚。在这里，我们结合使用流式细胞术、双光子成像和计算建模来定量 T 细胞-DC 相遇的概率。我们计算得出，在存在 10、100 和 1000 个携带 Ag 的 DC 的情况下，驻留在小鼠腘淋巴结中 24 小时的 T 细胞与 DC 相互作用的机会分别为 8%、58%和 99%。我们的结果揭示了 DC 数量存在一个阈值，低于该阈值，由于概率原因，T 细胞反应无法被引发。在小鼠中，我们估计，当从 10（-6）的前体频率开始时，至少需要 85 个 DC 才能启动 T 细胞反应。我们的结果对基于 DC 的疫苗的合理设计具有重要意义。
