感染是新生儿死亡的首要病因之一。胸腺病理性退化导致的免疫反应低下在新生儿败血症发生发展中起关键作用。我们前期研究发现：转录因子FOXN1具有促进胸腺上皮细胞（TECs）增殖、介导胸腺重建进而增强机体免疫功能的作用；新生儿败血症动物模型中胸腺FOXN1表达下调，伴有血管内皮生长因子(VEGF)通路表达平行下降。因此，我们推测FOXN1在新生儿感染胸腺发育、退化及重建过程中具有重要作用，VEGF是FOXN1的关键调控靶点。本课题拟应用前期克隆表达纯化的重组FOXN1（rFOXN1）蛋白，选用败血症新生动物模型及离体TECs，研究rFOXN1蛋白对胸腺结构和功能的影响，并探索其对退化胸腺的重建作用和对败血症的治疗效果；继而阻断VEGF信号通路，进一步探讨VEGF信号通路在rFOXN1蛋白调控机制中的作用。本课题将为新生儿败血症治疗，降低该病死亡率提供新的思路和途径。

Newborn are highly susceptible to infection, which remains important to neonatal mortality. Thymus involution plays a major role in the process of neonatal sepsis. The transcription factor Forkhead box N1 (FOXN1) is a master regulator in the development of thymic epithelial cells (TECs), and the activation of endogenous Foxn1 is as part of an initiated TEC differentiation program to enhancing immune system function. We found the expression of FOXN1 significantly decreased in the animal model of neonatal sepsis. We successfully cloned and expressed recombinant FOXN1 protein (rFOXN1) that was fused with cell-penetrating peptides. And we showed that administration of rFOXN1 into hematopoietic stem cell transplantation mice increased the number of TECs, promoted T cell regeneration and adaptive immunity. We also found that vascular endothelial growth factor(VEGF) of thymus contributed to the development of TECs in neonatal sepsis. So we hypothesize that FOXN1 is required not only for thymus development, but also for thymus involution and regeneration in neonatal sepsis, and VEGF pathway is involved. In this topic, we intend to apply the pre-purification rFOXN1 protein in vivo and in-vitro of neonatal sepsis models, to study the effect of rFOXN1 protein on the structure and function of the thymus, and explore its effect on thymus regeneration and the treatment of sepsis. Furthermore blocking the VEGF signaling pathway, we further explore the protective effect of rFOXN1 protein. This project will provide new ideas and approaches in neonatal sepsis treatment and reduce the mortality rate of the disease.