DataSheet_2_IL-21 is required for the maintenance and pathogenesis of murine Vγ4+ IL-17-producing γδT cells.doc

Murine IL-17-producing γδT (γδT17) cells are divided into two subsets: natural γδT17 (nγδT17) cells, whose development is restricted to the fetal thymus, and inducible γδT17 cells, which require antigen exposure for their IL-17 production and are presumed to develop from Rorc+Il17a-CCR9+ immature γδT17 cells in the adult thymus and whose T cell receptor (TCR) is biased toward Vγ4. Although IL-23 is known to be involved in developing γδT17 cells, the roles of other cytokines, such as IL-21, which is involved in developing Th17 cells like IL-23, in the development, maintenance, and pathophysiology of γδT17 cells remain unknown. Here, we show that IL-21 is dispensable for the fetal thymic development of nγδT17 cells but is required for the peripheral maintenance of Vγ4+nγδT17 cells. Upon stimulation with γδTCR, IL-1 plus IL-21 induces the proliferation of Vγ4+nγδT17 cells via STAT3 as effectively as IL-1 plus IL-23. Using bone marrow chimeric mice, we demonstrated that immature γδT17 cells are produced de novo in the adult mice from donor adult bone marrow cells and that IL-21 is dispensable for their development. Instead, IL-21 is required to expand newly induced Vγ4+γδT17 cells in the periphery upon immunization. Finally, using adoptive transfer experiments of γδT17 cells, we found that IL-21 receptors on γδT17 cells are involved in maintaining Vγ4+γδT17 cells, subsequent infiltration of Th17 cells into the spinal cord, and exacerbation of experimental autoimmune encephalomyelitis. Collectively, IL-21 plays a vital role in the maintenance and pathogenesis of Vγ4+γδT17 cells.

产白细胞介素17的γδT细胞（γδT17细胞）可分为两个亚群：天然型γδT17（nγδT17）细胞，其发育局限于胎儿胸腺；以及诱导型γδT17细胞，此类细胞需经抗原暴露方可产生IL-17，推测其起源于成年胸腺内的Rorc+Il17a-CCR9+未成熟γδT17细胞，且其T细胞受体（TCR）偏向Vγ4亚型。尽管已知白细胞介素23（IL-23）参与γδT17细胞的发育过程，但其他细胞因子——如与IL-23一同参与Th17细胞发育的白细胞介素21（IL-21）——在γδT17细胞的发育、维持及病理生理过程中的作用仍未明确。本研究发现，IL-21对nγδT17细胞的胎儿胸腺发育非必需，但对Vγ4+nγδT17细胞的外周维持不可或缺。经γδTCR刺激后，IL-1联合IL-21可通过信号转导与转录激活因子3（STAT3）有效诱导Vγ4+nγδT17细胞增殖，其诱导效率与IL-1联合IL-23相当。利用骨髓嵌合小鼠模型，我们证实成年小鼠体内可由供体成年骨髓细胞从头生成未成熟γδT17细胞，且IL-21对该细胞的发育过程非必需。与之相反，免疫接种后，IL-21是外周中新诱导的Vγ4+γδT17细胞扩增所必需的条件。最后，通过γδT17细胞过继转移实验，我们发现γδT17细胞表面的IL-21受体参与维持Vγ4+γδT17细胞群、后续Th17细胞向脊髓的浸润，以及加重实验性自身免疫性脑脊髓炎（experimental autoimmune encephalomyelitis）的病情。综上，IL-21在Vγ4+γδT17细胞的维持及致病过程中发挥关键作用。