异体MSCs通过FLT3L上调CD1c+耐受性DCs治疗SLE的机制研究

CD1c+DCs are a typical tolerogenic dendritic cell subtype, but whether it play a role in the pathogenesis of systemic lupus erythematosus (SLE) remains largely unknown. Umbilical cord (UC)-derived mesenchymal stem cells (MSCs) transplantation (U-MSCT) is an effective method in treating refractory SLE. We have previous detected the reduced number of CD1c+DCs in active SLE patients, which is significantly correlated with their disease activity. After U-MSCT, the number of CD1c+DCs remarkably increased, but the underlined mechanism remained incompletely understood. The cytokine FLT3 Ligand (fms-like tyrosine kinase-3 ligand, FLT3L) is a key regulator of DCs commitment in hematopoiesis, FLT3L injection increases CD1c+ DCs as well as their precursors, so we speculate that FLT3L plays an important role in initiating UC-MSCs to regulate the number and function of CD1c+DCs. In the current study, we will determine that in SLE microenvironment, IFN-γ/IL-6 stimulates MSCs to produce FLT3L via JAK-STAT pathways, and then to up-regulate CD1c+DCs. On the other hand, MSCs can directly modulate the number and function of CD1c+DCs both in vivo and in vitro. Here we will illustrate how allogenic MSCs interact with lupus microenvironment and directly/indirectly modulate tolerogenic DCs activity. The conclusion of this study may provide further insight in understanding the mechanisms by which UC-MSCs effectively treat SLE patients.

CD1c+耐受性树突状细胞（DCs）是公认的新型耐受性DCs亚群 ，但其在系统性红斑狼疮（SLE）发病中的作用仍未知。脐带间充质干细胞（UC-MSCs）移植是一种治疗难治性SLE的有效方法。前期研究已观察到，CD1c+DCs数量在活动性SLE患者中显著降低，并与疾病活动度相关，而UC-MSCs移植后CD1c+DCs数量显著上升，但具体机制尚不清楚。既往文献报道Fms样酪氨酸激酶3配体（FLT3L）促进CD1c+DCs数量增加，因此我们推测FLT3L在启动UC-MSCs调控CD1c+DCs数量和功能中发挥重要作用。本课题拟进一步探讨SLE微环境中的炎性因子通过JAK-STAT途径刺激UC-MSCs表达FLT3L，上调SLE患者CD1c+DCs数量并改善其功能，深入阐明UC-MSCs与SLE内环境相互作用及调控耐受性DCs的可能机制，为UC-MSCs移植治疗SLE患者奠定理论基础。

脐带来源的间充质干细胞（UC MSCs）在治疗SLE中发挥重要的免疫调节作用，并且与SLE炎性内环境密切相关，但是该作用是否通过调控耐受性DCs仍不清楚。本研究证实了SLE患者外周血中CD1c+ tolDCs数量显著降低，并且与疾病活动度呈显著正相关，合并狼疮肾炎的SLE患者较肾功能正常的患者CD1c+ tolDCs降低更为显著。SLE患者血浆中FLT3L的水平也显著降低，并且与CD1c+ tolDCs水平呈正相关。UC MSCs移植可显著上调SLE患者外周血CD1c+ tolDCs的数量，同时伴有血浆中FLT3L水平升高；体外用UC MSCs和SLE PBMC共培养均可显著上调CD1c+ tolDCs的数量和共培养上清中FLT3L的水平，并且具有时间依赖性。UC MSCs表达FLT3L，CD1c+ tolDCs表达FLT3L的受体FLT3。此外，UC MSCs上调CD1c+ tolDCs是通过UC MSCs和CD1c+ tolDCs直接接触，促进后者细胞增殖，抑制细胞凋亡，但是对其分化没有明显影响；通过siRNA抑制UC MSCs上FLT3L的表达，该过程被逆转，同时UC MSCs上调CD1c+ tolDCs的能力下降。另一方面，SLE PBMC、SLE血浆和IFN-γ均能显著增加UC MSCs FLT3L的表达。在SLE PBMC与UC MSCs的共培养体系中加入抗IFN-γ的单克隆抗体一方面逆转UC MSCs上调CD1c+ tolDCs的过程，另一方面降低UC MSCs FLT3L的表达。同时发现SLE PBMC和IFN-γ促进UC MSCs JAK/STAT通路活化，该作用可以被抗IFN-γ单克隆抗体逆转；此外，IFN-γ促进UC MSCs表达FLT3L的过程可被JAK/STAT通路抑制剂AG490逆转。因此，我们的研究证明了CD1c+ tolDCs是参与调控SLE患者免疫耐受的重要DC亚群，揭示了IFNγ-FLT3L-FLT3轴在脐带MSCs治疗SLE中促进CD1c+ tolDCs增殖、抑制凋亡从而上调其数量过程中发挥的重要作用；阐明了UC MSCs通过调控耐受性DCs，在免疫反应的初始阶段诱导免疫耐受的全新机制，为UC MSCs治疗SLE提供了新的理论依据。