VEGFR-3 Stimulation on LECs Boosts Type 2 Immunity After Vaccination

Abstract

Abstract Lymphatic vessels are the main transport routes for fluid, antigens, exosomes, and immune cells from peripheral tissues to the lymph nodes (LNs). In addition to being pervasive through tissue, lymphatic vessels are also abundant within the LN, where they route lymph and cells around the B cell follicles and throughout the paracortical zone; thus, lymphatic endothelial cells (LECs) have unique access to lymph-borne molecules and interactions with immune cells. Upon acute inflammation or vaccination, LN LECs undergo expansion along with lymphocyte proliferation, a process dependent on the VEGF-C/VEGFR-3 signaling axis; however, it is not well understood how LN lymphatics and their expansion contribute to acute adaptive immune responses. Here, we asked how altering VEGFR-3 signaling LN LECs alters the adaptive immune response, using OVA + CpG (a TLR9 agonist) as a model for vaccination. We found that delivering VEGF-C156S, a VEGFR-3 specific agonist, multiple times prior to and concurrent with the inflammatory stimulus led to increased Th2 responses in terms of higher plasma levels of OVA-specific IgG1, more IgG1+ germinal center B cells, and increased production of Th2 cytokines (IL-4, IL-5, and IL-13) by CD4+ T cells upon restimulation. In loss-of-function experiments using a tamoxifen-inducible LEC-specific deletion of VEGFR-3, vaccination led to reduced plasma levels of OVA-specific IgG1 compared to tamoxifen-treated control littermates. Together, these findings suggest that in response to vaccination, VEGFR-3 signaling in LN LECs bias adaptive immune responses towards type 2 immunity. This highlights the role of lymphatics not just as passive conduits for fluid transport, but as having direct immunomodulatory function.