The role of lymph flow in regulation of innate immunity

在免疫刺激后，淋巴管将抗原、调节因子和细胞运送到淋巴结(LN)，以启动保护性免疫。免疫反应在LN(先天免疫和获得性免疫)中及时发生，每一步都依赖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，因此知之甚少。淋巴成分在免疫刺激后迅速变化。利用金黄色葡萄球菌(S.aureus)皮肤感染作为免疫刺激模型，我们将研究淋巴如何调节中性粒细胞的迁移，作为LN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的先天免疫保护。传入淋巴管在几分钟内将淋巴输送到LN，使感染区域的变化及时到达LN。在LN中，淋巴沿着一种称为管道的特殊网络流动，将小分子抗原和调节因子高效地输送到LN实质中的指定位置。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，以获得最佳的LNS免疫反应。在金黄色葡萄球菌皮肤感染后，中性粒细胞是第一大群循环中的白细胞，迅速渗透到感染的皮肤和引流的LN，以消除细菌，防止其全身传播。在感染后的前4小时(4hpi)，中性粒细胞主要从高内皮微静脉(HEV)渗入LN。HEV是一种特殊的LN血管，允许免疫细胞在体内平衡状态下归巢到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做出反应？在初步研究中，我们发现阻断传入淋巴管抑制了中性粒细胞在LN中的迁移，但在感染金黄色葡萄球菌的皮肤区域却没有。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足以在LN中招募中性粒细胞。我们推测，在感染的早期阶段，淋巴管将细菌和淋巴中的免疫调节因子输送到LN，并通过管道将淋巴携带的免疫调节因子传递给HEV，以指导中性粒细胞的迁移。淋巴流动受损可阻断中性粒细胞在LN中的迁移。为了验证这一假说，我们将剖析阻断传入淋巴管(目标1)、阻断传出淋巴管(目的2)和改变沿管道的淋巴流动(目的3)如何调节LN中性粒细胞的迁移。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.