Pan Deng, Hunter Daniel A, Schellhardt Lauren, Fuchs Anja, Halevi Alexandra E, Snyder-Warwick Alison K, Mackinnon Susan E, Wood Matthew D
Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
Section of Acute and Critical Care Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA.
Acta Biomater. 2020 Aug;112:149-163. doi: 10.1016/j.actbio.2020.05.009. Epub 2020 May 17.
Decellularized nerve, or acellular nerve allografts (ANAs), are an increasingly used alternative to nerve autografts to repair nerve gaps to facilitate regeneration. The adaptive immune system, specifically T cells, plays a role in promoting regeneration upon these ANA scaffolds. However, how T cells promote regeneration across ANAs is not clear. Here, we show that T cells accumulate within ANAs repairing nerve gaps resulting in regulation of cytokine expression within the ANA environment. This in turn ultimately leads to robust nerve regeneration and functional recovery. Nerve regeneration across ANAs and functional recovery in Rag1KO mice was limited compared to wild-type (WT) mice. Prior to appreciable nerve regeneration, ANAs from Rag1KO mice contained fewer eosinophils and reduced IL-4 expression compared to ANAs from WT mice. During this period, both T cells and eosinophils regulated IL-4 expression within ANAs. Eosinophils represented the majority of IL-4 expressing cells within ANAs, while T cells regulated IL-4 expression. Finally, an essential role for IL-4 during nerve regeneration across ANAs was confirmed as nerves repaired using ANAs had reduced regeneration in IL-4 KO mice compared to WT mice. Our data demonstrate T cells regulate the expression of IL-4 within the ANA environment via their effects on eosinophils. STATEMENT OF SIGNIFICANCE: The immune system has been emerging as a critical component for tissue regeneration, especially when regeneration is supported upon biomaterials. The role of T cells, and their roles in the regeneration of nerve repaired with biomaterials, is still unclear. We demonstrated that when nerves are repaired with decellularized nerve scaffolds, T cells contribute to regeneration by regulating cytokines. We focused on their regulation of cytokine IL-4. Unexpectedly, T cells do not produce IL-4, but instead regulate IL-4 by recruiting eosinophils, which are major cellular sources of IL-4 within these scaffolds. Thus, our work demonstrated how IL-4 is regulated in a model biomaterial, and has implications for improving the design of biomaterials and understanding immune responses to biomaterials.
去细胞神经，即脱细胞神经同种异体移植物（ANA），作为神经自体移植物的替代物，在修复神经缺损以促进再生方面的应用越来越广泛。适应性免疫系统，特别是T细胞，在这些ANA支架上促进再生过程中发挥作用。然而，T细胞如何促进ANA上的神经再生尚不清楚。在此，我们表明T细胞在修复神经缺损的ANA内聚集，从而调节ANA环境中的细胞因子表达。这最终又导致强大的神经再生和功能恢复。与野生型（WT）小鼠相比，Rag1基因敲除（Rag1KO）小鼠中通过ANA的神经再生和功能恢复受到限制。在明显的神经再生之前，与WT小鼠的ANA相比，Rag1KO小鼠的ANA中嗜酸性粒细胞较少且白细胞介素-4（IL-4）表达降低。在此期间，T细胞和嗜酸性粒细胞均调节ANA内的IL-4表达。嗜酸性粒细胞是ANA内表达IL-4的主要细胞类型，而T细胞调节IL-4表达。最后，通过与WT小鼠相比，使用ANA修复的神经在IL-4基因敲除（IL-4KO）小鼠中的再生减少，证实了IL-4在通过ANA的神经再生过程中的重要作用。我们的数据表明T细胞通过其对嗜酸性粒细胞的作用来调节ANA环境中IL-4的表达。重要性声明：免疫系统已逐渐成为组织再生的关键组成部分，尤其是当再生由生物材料支持时。T细胞的作用及其在生物材料修复神经再生中的作用仍不清楚。我们证明，当用去细胞神经支架修复神经时，T细胞通过调节细胞因子促进再生。我们重点研究了它们对细胞因子IL-4的调节。出乎意料的是，T细胞不产生IL-4，而是通过募集嗜酸性粒细胞来调节IL-4，嗜酸性粒细胞是这些支架内IL-4的主要细胞来源。因此，我们的工作展示了在一种模型生物材料中IL-4是如何被调节的，并且对于改进生物材料设计和理解对生物材料的免疫反应具有重要意义。
