Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH), Bethesda, MD, United States.
Biological Imaging Section, Collaborative Research Technologies Branch (CRT), NIAID, NIH, Bethesda, MD, United States.
Front Immunol. 2024 Aug 12;15:1427509. doi: 10.3389/fimmu.2024.1427509. eCollection 2024.
The successful development of germinal centers (GC) relies heavily on innate mechanisms to amplify the initial inflammatory cascade. In addition to their role in antigen presentation, innate cells are essential for the redirection of circulating lymphocytes toward the draining lymph node (dLN) to maximize antigen surveillance. Sphingosine-1-Phosphate (S1P) and its receptors (S1PR1-5) affect various aspects of immunity; however, the role of S1PR4 in regulating an immune response is not well understood. Here we use a footpad model of localized T1 inflammation to carefully monitor changes in leukocyte populations within the blood, the immunized tissue, and the dLN. Within hours of immunization, neutrophils failed to adequately mobilize and infiltrate into the footpad tissue of S1PR4 mice, thereby diminishing the local vascular changes thought to be necessary for redirecting circulating cells toward the inflamed region. Neutrophil depletion with anti-Ly6G antibodies significantly reduced early tissue edema as well as the redirection and initial accumulation of naïve lymphocytes in dLN of WT mice, while the effects were less prominent or absent in S1PR4 dLN. Adoptive transfer experiments further demonstrated that the lymphocyte homing deficiencies were not intrinsic to the donor S1PR4 lymphocytes, but were instead attributed to differences within the S1PR4-deficient host. Reduced cell recruitment in S1PR4 mice would seed the dLN with fewer antigen-respondent lymphocytes and indeed, dLN hypertrophy at the peak of the immune response was severely diminished, with attenuated GC and activation pathways in these mice. Histological examination of the S1PR4 dLN also revealed an underdeveloped vascular network with reduced expression of the leukocyte tethering ligand, PNAd, within high endothelial venule regions, suggesting inadequate growth of the dLN meant to support a robust GC response. Thus, our study reveals that S1PR4 may link early immune modulation by neutrophils to the initial recruitment of circulating lymphocytes and downstream expansion and maturation of the dLN, thereby contributing to optimal GC development during an adaptive response.
生发中心（GC）的成功发育在很大程度上依赖于先天机制来放大初始炎症级联。除了在抗原呈递中的作用外，先天细胞对于将循环淋巴细胞重新定向到引流淋巴结（dLN）以最大程度地进行抗原监测也是必不可少的。1-磷酸鞘氨醇（S1P）及其受体（S1PR1-5）影响免疫的各个方面；然而，S1PR4 调节免疫反应的作用尚不清楚。在这里，我们使用局部 T1 炎症的足底模型仔细监测白细胞群体在血液、免疫组织和 dLN 中的变化。在免疫后数小时内，中性粒细胞未能充分动员并浸润到 S1PR4 小鼠的足底组织中，从而减少了局部血管变化，这些变化被认为对于将循环细胞重新定向到炎症区域是必要的。用抗 Ly6G 抗体耗尽中性粒细胞会显著减少早期组织水肿以及 WT 小鼠 dLN 中幼稚淋巴细胞的重新定向和初始积累，而在 S1PR4 dLN 中，这些影响不太明显或不存在。过继转移实验进一步表明，淋巴细胞归巢缺陷不是供体 S1PR4 淋巴细胞固有的，而是归因于 S1PR4 缺陷宿主内的差异。S1PR4 小鼠中细胞募集减少会使 dLN 中具有更少的抗原反应性淋巴细胞，实际上，在免疫反应高峰期，dLN 肥大严重减少，这些小鼠中的 GC 和激活途径减弱。对 S1PR4 dLN 的组织学检查还揭示了一个发育不良的血管网络，高内皮静脉区域内的白细胞黏附配体 PNAd 表达减少，这表明支持强大 GC 反应的 dLN 生长不足。因此，我们的研究表明，S1PR4 可能将中性粒细胞的早期免疫调节与循环淋巴细胞的初始募集以及下游 dLN 的扩张和成熟联系起来，从而有助于适应性反应期间最佳 GC 的发育。
