title: Lymph Node Stromal Network-Guided Lymph Drainage Regulates Neutrophil Response to S. aureus Infection
Creators: name: Xue, Jingna
Publisher: name: Cumming School of Medicine
Year: 2024
Subjects: subject: Lymphatic system
subject: lymph drainage
subject: Infection
subject: Fibroblast reticular cells
subject: Conduit network
subject: Neutrophils
subject: Education--Health
subject: Bioinformatics
subject: FOS: Computer and information sciences
subject: Immunology
subject: FOS: Clinical medicine
subject: Microbiology
subject: FOS: Biological sciences

description: The lymph transports various molecules (i.e., tissue waste, antigens, immunoregulators, cells) to the lymph nodes (LNs). A unique LN conduit network made by fibroblastic reticular cells (FRC-conduit network) guides the drainage of lymph-derived molecules inside the LNs from entry to exit, as well as to high endothelial venules (HEVs) efficiently. Thereby, lymph drainage ensures timely immune protection. Within 4 hour-post-Staphylococcus aureus skin infection (4hpi), neutrophils infiltrate the LN through HEVs and prevent systemic S. aureus dissemination. The mechanism of this efficient recruitment and the connection between skin and LN was not fully understood. Here, I found that the timely neutrophil migration from HEV relies on lymph drainage using a lymphatic occlusion model. Further studies showed that the essential regulatory factors drained with lymph that regulate neutrophil recruitment in the LN are infection-induced chemokines (i.e., CXCL1 and CXCL2) rather than bacteria. Infection often occurs with complicated pre-existing conditions, potentially due to the pre-altered host immune environment. Using Oxazolone (OX)-induced skin inflammation, I observed an interrupted FRC-conduit network and reduced lymph reaching HEV in the LN. When infection occurs during OX-induced inflammation, I found altered neutrophil distribution, which diminished interaction with bacteria and a decreased CXCL1/2 level in the LN. A prolonged bacterial clearance was also observed in OX-inflamed LN, and a trend of systemic bacterial spreading was found in OX-induced inflammation. Next, I investigated the mechanism by which the FRC-conduit network is altered and explored whether targeting the FRC-conduit network can improve neutrophil response. Using single-cell RNA sequencing (scRNAseq) and immunofluorescence staining, I characterized the alteration of FRC subsets and plotted the changes to the LN niches. Notably, I identified a new FRC subset, Cxcl13inter RCs, generated in the OX-inflamed LNs, which only produce low levels of conduit components and thus cause a conduit loss. The induction of this new subset is from proliferative adjacent FRCs depending on B cell-derived lymphotoxins. Depletion of B cells eliminates the induction of Cxcl13inter RCs and preserves the conduit network and lymph drainage to HEVs. Upon subsequent S. aureus infection, the neutrophil response was also rescued, which is associated with better restrained systemic bacteria dissemination. Overall, this thesis demonstrates that lymph drainage guided by the FRC-conduit network in the LNs is critical to ensure optimal neutrophil migration and timely innate immune protection in S. aureus infection.