Skin antigens in the steady state are trafficked to regional lymph nodes by transforming growth factor-β1-dependent cells

Antigen capturing in the skin and antigen trafficking into regional lymph nodes (LN) initiate immune responses. In this study, employing melanin granule (MG) as an easily traceable antigen in two mouse strains that carried steel factor or hepatocyte growth factor transgenes and had melanocytosis in the epidermis or in the dermis respectively, we investigated the mechanism of antigen trafficking from the skin. MG captured in the epidermis or dermis accumulated in the regional LN, but not other tissues. Only in alymphoplastic mice did MG-laden cells pass through the lymphatics and reached many tissues. Since inflammatory regions were not observed in the skin of either type of transgenic mouse, our developmental system enables us to investigate constitutive capturing and trafficking of insoluble antigens in the steady state. Both dendritic cells and macrophages were laden with MG in the regional LN. To determine which cells traffic antigens to the LN, we prepared double mutants that carried the transgenes and lacked transforming growth factor (TGF)-β1, since mice lacking TGF-β1 are reported to be deficient of Langerhans cells. Few MG were observed in the regional LN of these double-mutant mice. We also showed that signaling via macrophage colony stimulating factor receptor or Flt3/Flk2 is not essential for development of the cells for this antigen trafficking. These results indicate that antigens in the epidermis and dermis in the steady state are trafficked into regional LN only by TGF-β1-dependent cells, which may be a dendritic cell lineage.