Figure 2.

Pathways of Ag acquisition and presentation by LECs. Several pathways of antigen (Ag) acquisition and loading coexist in lymphatic endothelial cells (LECs). Interactions with dendritic cells (DCs) underlie complex mechanisms of Ag transfer in both directions. On one hand, LECs act as Ag reservoirs for DCs which can uptake LEC-derived Ag. The mechanisms accounting for this phenomenon remain however unclear. On the other hand, LECs acquire peptide–MHC-II complexes from DCs in a cell–cell contact dependent manner (DC-derived Ag is depicted in yellow). DC-derived exosomes might also be implicated. Peripheral tissue-restricted Ags (PTA) (in pink) expressed by LEC can be loaded into MHC-I molecules. Intracellular pathways of degradation of such PTAs have however been not investigated. Moreover, whether PTA can be incorporated in MHC-II compartments is still a matter of debate. Alternatively, LECs possess the ability to uptake exogenous lymph-borne and tumor-derived Ag that can be incorporated in MHC-I pathway in a TAP-1-dependent manner. Related references are indicated in numbers.