Platelets enhance CD4+ central memory T cell responses via platelet factor 4-dependent mitochondrial biogenesis and cell proliferation

Platelets regulate multiple aspects of CD4⁺ T cell immunity, and may exert distinct regulations among different T cell subsets. Our aim was to investigate how platelets regulate CD4⁺ central memory T cell (Tcm) responses. αCD3/αCD28-stimulated human CD4⁺ Tcm cells were cultured without or with platelets or platelet-derived mediators. Polyclonal stimulation induced cell proliferation and Th1 and Treg cell activation of Tcm cells. Platelet factor 4/PF4 neutralization abolished platelet-enhanced Tcm effector responses, whilst TGFβ neutralization only partially inhibited platelet-enhanced Treg cell activation. PF4 supplementation mimicked the effects of platelet co-cultures, while PF4 receptor CXCR3 blockade and CXCR3 knockdown with siRNAs inhibited or abolished PF4-enhanced Th1 and Treg cell responses. Platelet co-cultures or PF4-treatment increased Tcm cell proliferation, whilst CXCR3 blockade counteracted. PF4-enhanced Tcm proliferation and effector cell responses were associated with mitochondrial biogenesis. Overexpression of mitochondrial transcription factor A (TFAM) mimicked PF4 effects, and PF4 treatment attenuated Akt phosphorylation of activated Tcm cells, leading to mitochondrial biogenesis. Impacts of platelets and PF4 on Tcm proliferation were further confirmed by that CXCR3 knockdown/blockade counteracted PF4-enhanced Tcm cell proliferation. In conclusion, platelets enhance Th1 and Treg cell responses of CD4⁺ Tcm cells, via PF4-dependent mitochondrial biogenesis and cell proliferation of Tcm cells.

血小板可调控CD4+ T细胞免疫的多个环节，并可对不同T细胞亚群发挥差异化调控作用。本研究旨在探究血小板如何调控CD4+中枢记忆T细胞（central memory T cell，Tcm）的应答反应。我们将经αCD3/αCD28刺激的人CD4+ Tcm细胞分别于无添加、添加血小板或血小板源性介质的条件下进行体外培养。多克隆刺激可诱导Tcm细胞增殖，以及辅助性T细胞1（T helper 1，Th1）和调节性T细胞（regulatory T cell，Treg）的活化。血小板因子4（platelet factor 4，PF4）的中和作用可消除血小板对Tcm效应细胞应答的增强效应，而转化生长因子β（transforming growth factor β，TGFβ）的中和作用仅能部分抑制血小板对Treg细胞活化的增强作用。补充PF4可模拟血小板共培养的效应，而使用小干扰RNA（small interfering RNA，siRNAs）敲低CXCR3或阻断CXCR3受体，则可抑制甚至消除PF4对Th1和Treg细胞应答的增强作用。血小板共培养或PF4处理可增强Tcm细胞的增殖，而CXCR3阻断可抵消这一效应。PF4介导的Tcm细胞增殖与效应细胞应答，与线粒体生物发生（mitochondrial biogenesis）密切相关。过表达线粒体转录因子A（mitochondrial transcription factor A，TFAM）可模拟PF4的作用效果，而PF4处理可减弱活化Tcm细胞的Akt磷酸化水平，进而促进线粒体生物发生。CXCR3敲低/阻断可抵消PF4对Tcm细胞增殖的增强作用，这一结果进一步验证了血小板与PF4对Tcm细胞增殖的影响。综上，血小板可通过依赖PF4的线粒体生物发生途径以及促进Tcm细胞增殖，增强CD4+ Tcm细胞的Th1和Treg细胞应答。