Specialized mesenteric lymphatic capillaries by-pass the mesenteric lymph node chain to transport peritoneal antigens directly into mediastinal lymph nodes

Lymphatic vessels (LVs) are indispensable for tissue fluid homeostasis and immune cell trafficking. The network of LVs that channel fluids from the gut into mesenteric lymph nodes (MLN) has been recognized as the sole lymphatic system in the mesentery. Here we describe an alternative, functionally autonomous set of capillary mesenteric LVs (capMLVs) that by-pass the MLNs and drain directly into mediastinal LNs. CapMLVs develop perinatally from valves of collective mesenteric lymphatic vessels (colMLVs) in response to arterial endothelial cell-derived VEGF-C. Once extended, capMLVs detach from colMLVs to form an independent elongated network comprised of LYVE1+, CCL21+ endothelial cells. Avascular areas of the mesentery juxtaposed to capMLVs contain cell islets that express ACKR4. This CCL21-scavenging atypical receptor facilitates the migration of mesenteric phagocytes into capMLVs to be channeled directly into mediastinal LNs. This allows peritoneum-derived ominous antigens to be processed separately from alimentary antigens.