Two lymph nodes draining the mouse liver are the preferential site of DC migration and T cell activation

Lymph nodes (LNs) play a critical role in host defence against pathogens. In rodents, lymphatic anatomy and drainage have been characterized for many different organs. Surprisingly, the LNs draining the mouse liver have not been clearly identified. This knowledge is of central importance to allow accurate characterization of immune responses to pathogens infecting the liver. It is also important for exploring immune responses in hepatic tumour models, and mechanisms underlying the relative tolerogenic properties of the liver. In this study, we used both anatomical and immunological approaches to identify the LN(s) draining the mouse liver.Evans Blue and purified dendritic cells were directly injected into the hepatic parenchyma.Using Evans Blue, we identified three LNs adjacent to the liver that stained with the dye within the first 5 min, which we termed portal, coeliac, and first mesenteric LNs. We also provide evidence that dendritic cells (DCs) injected under the liver capsule preferentially migrate to the coeliac and portal nodes, leading to local activation of antigen-specific naïve CD8 and CD4 T cells, suggesting this is a route of lymphatic drainage from the liver. Consistent with this result, cell-associated antigen injected under the liver capsule was also cross-presented to CD8 T cells in these nodes.These results suggest for the first time that the coeliac and portal nodes are the main LNs draining the liver, and that DCs exiting the liver can elicit primary T cell activation within these lymph nodes; first mesenteric nodes play a secondary role. We propose this nomenclature to be used as common designations for the observed structures.