The role of lymph flow in regulation of innate immunity

免疫刺激后，淋巴管将抗原、调节因子和细胞运送到淋巴结（LN），启动保护性免疫。LN中的免疫反应（先天免疫和适应性免疫）及时发生，每一步都取决于一定程度的淋巴管功能。然而，淋巴在免疫调节中的作用往往被忽视，因此人们对其了解甚少。免疫刺激后淋巴成分迅速改变。以金黄色葡萄球菌（S. aureus）皮肤感染为免疫刺激模型，我们将研究淋巴如何调节中性粒细胞迁移作为LN中宿主免疫防御的早期步骤。我们研究的长期目标是阐明淋巴如何调节LN中的先天免疫保护。传入淋巴管在几分钟内将淋巴液运送到淋巴结，使感染区域的变化及时到达淋巴结。在LN中，淋巴沿着一个被称为导管的特殊网络流动，将小分子量抗原和调节因子有效地递送到LN薄壁组织的指定位置。免疫监视后，淋巴和细胞通过传出淋巴管离开LN。淋巴和细胞的运动被微调为最佳的免疫反应在LNs。金黄色葡萄球菌皮肤感染后，中性粒细胞是第一大群循环白细胞，迅速渗透到感染皮肤和引流LN中，以消灭细菌并防止其全身扩散。在感染后的头4小时（4hpi），中性粒细胞主要从高内皮小静脉（hev）浸润LN。hev是专门的LN血管，允许免疫细胞在稳态状态下归巢到LN。然而，中性粒细胞很少在稳态状态下进入LN。LN中的hev如何在如此短的时间内对皮肤感染作出反应？在初步研究中，我们发现阻断传入淋巴管可以抑制LN中中性粒细胞的迁移，但对金黄色葡萄球菌感染的皮肤区域没有作用。没有淋巴流动，LN中的细菌不能有效地招募中性粒细胞。另外，皮肤中的中性粒细胞迁移趋化因子CXCL1和CXCL2足以募集LN中的中性粒细胞。我们推测，在感染早期，淋巴管将淋巴液中的细菌和免疫调节因子转运到淋巴结，而导管将淋巴性免疫调节因子转运到hev，指导中性粒细胞迁移。受损的淋巴流动阻断了LN中中性粒细胞的迁移。为了验证这一假设，我们将剖析如何阻断传入淋巴管（目的1）；阻断传出淋巴管（Aim 2）和改变淋巴管的淋巴流动（Aim 3）调节LN中的中性粒细胞迁移。我们的研究计划将揭示淋巴如何参与LN免疫调节的基本机制。

After an immune stimulation, lymphatic vessels transport antigens, regulatory factors, and cells to the lymph node (LN) to initiate protective immunity. Immune responses in the LN (innate and adaptive immunity) take place in a timely manner, and each step depends on some degree of functional lymphatic vessels. However, the role of lymph in immune regulation is often ignored and thus is poorly understood. The lymph composition rapidly changes after an immune stimulation. Using Staphylococcus aureus (S. aureus) skin infection as an immune stimulation model, we will study how lymph regulates neutrophil migration as an early step of host immune defense in the LN. The long-term goal of our study is to elucidate how lymph regulates innate immune protection in the LN. Afferent lymphatic vessels transport lymph to the LN in a matter of minutes allowing changes in the infected area to reach the LN timely. In the LN, lymph flows along a specialized network called conduits to deliver small molecular weight antigens and regulatory factors to their designated locations in the LN parenchyma efficiently. After immune surveillance, lymph and cells exit the LN via efferent lymphatic vessels. The movement of lymph and cells is finely tuned for optimal immune responses in the LNs. After S. aureus skin infection, neutrophils are the first large population of circulating leukocytes to rapidly infiltrate the infected skin and the draining LN to eliminate the bacteria and prevent their systemic spread. In the first 4 hours post-infection (4hpi), neutrophils predominantly infiltrate the LN from high endothelial venules (HEVs). HEVs are specialized LN blood vessels that allow immune cell homing to the LN in homeostatic status. However, neutrophils rarely enter the LN in homeostasis. How can HEVs in the LN react to skin infection in such a short time frame? In preliminary studies, we have found that blocking afferent lymphatic vessels inhibited neutrophil migration in the LN, but not in the skin area infected by S. aureus. Without lymph flow, bacteria in the LN could not effectively recruit neutrophils. Alternatively, neutrophil migration chemokines, CXCL1 and CXCL2, in the skin were sufficient to recruit neutrophils in the LN. We hypothesize that in the early stage of infection, lymphatic vessels transport bacteria and immune regulatory factors in lymph to the LN, and conduits relay lymph-borne immune regulatory factors to HEVs to direct neutrophil migration. Impaired lymph flow interrupts neutrophil migration in the LN. To test this hypothesis, we will dissect how blocking afferent lymphatic vessels (Aim 1); blocking efferent lymphatic vessels (Aim 2) and changing lymph flow along the conduits (Aim 3) regulate neutrophil migration in the LN. Our research program will reveal fundamental mechanism of how lymph participates in immune regulation in the LN.