Research Unit, Saskatchewan Cancer Agency, Department of Oncology, University of Saskatchewan, Saskatoon, Saskatchewan Canada.
J Leukoc Biol. 2012 Aug;92(2):289-300. doi: 10.1189/jlb.1211631. Epub 2012 Apr 27.
CD4(+) T cell help contributes critically to DC-induced CD8(+) CTL immunity. However, precisely how these three cell populations interact and how CD4(+) T cell signals are delivered to CD8(+) T cells in vivo have been unclear. In this study, we developed a novel, two-step approach, wherein CD4(+) T cells and antigen-presenting DCs productively engaged one another in vivo in the absence of cognate CD8(+) T cells, after which, we selectively depleted the previously engaged CD4(+) T cells or DCs before allowing interactions of either population alone with naïve CD8(+) T cells. This protocol thus allows us to clearly document the importance of CD4(+) T-licensed DCs and DC-primed CD4(+) T cells in CTL immunity. Here, we provide direct in vivo evidence that primed CD4(+) T cells or licensed DCs can stimulate CTL response and memory, independent of DC-CD4(+) T cell clusters. Our results suggest that primed CD4(+) T cells with acquired pMHC-I from DCs represent crucial "immune intermediates" for rapid induction of CTL responses and for functional memory via CD40L signaling. Importantly, intravital, two-photon microscopy elegantly provide unequivocal in vivo evidence for direct CD4-CD8(+) T cell interactions via pMHC-I engagement. This study corroborates the coexistence of direct and indirect mechanisms of T cell help for a CTL response in noninflammatory situations. These data suggest a new "dynamic model of three-cell interactions" for CTL immunity derived from stimulation by dissociated, licensed DCs, primed CD4(+) T cells, and DC-CD4(+) T cell clusters and may have significant implications for autoimmunity and vaccine design.
CD4(+) T 细胞的辅助作用对于 DC 诱导的 CD8(+) CTL 免疫至关重要。然而，这三种细胞群体如何相互作用，以及 CD4(+) T 细胞信号如何在体内传递给 CD8(+) T 细胞，目前还不清楚。在这项研究中，我们开发了一种新颖的两步法，其中 CD4(+) T 细胞和抗原呈递 DC 在体内相互作用，而没有与 CD8(+) T 细胞的同源性，之后，我们选择性地耗尽之前参与的 CD4(+) T 细胞或 DC，然后允许单独的任何一种群体与幼稚的 CD8(+) T 细胞相互作用。因此，该方案允许我们清楚地证明 CD4(+) T 细胞许可的 DC 和 DC 激活的 CD4(+) T 细胞在 CTL 免疫中的重要性。在这里，我们提供了直接的体内证据，证明激活的 CD4(+) T 细胞或许可的 DC 可以刺激 CTL 反应和记忆，而无需 DC-CD4(+) T 细胞簇。我们的结果表明，从 DC 获得 pMHC-I 的激活的 CD4(+) T 细胞代表了快速诱导 CTL 反应和通过 CD40L 信号传递功能记忆的关键“免疫中间物”。重要的是，活体双光子显微镜优雅地提供了直接的 CD4-CD8(+) T 细胞相互作用的明确体内证据，通过 pMHC-I 结合。这项研究证实了在非炎症情况下，CTL 反应中 T 细胞辅助的直接和间接机制并存。这些数据为源自分离的、许可的 DC、激活的 CD4(+) T 细胞和 DC-CD4(+) T 细胞簇刺激的 CTL 免疫提出了一种新的“三细胞相互作用的动态模型”，并可能对自身免疫和疫苗设计具有重要意义。
