Langerhans cells transport Leishmania major from the infected skin to the draining lymph node for presentation to antigen-specific T cells.

Murine epidermal Langerhans cells (LC) have been shown to internalize Leishmania major, a cause of human cutaneous leishmaniasis, and to stimulate a vigorous parasite-specific T cell response. The present study emphasizes the critical role of LC in leishmaniasis by documenting directly that LC have the ability to transport L. major from the skin to the draining lymph node (LN). This was revealed by irreversible labeling of LC with a fluorescent cell linker and in vivo tracking. In contrast, no migration to the LN was seen with L. major-infected macrophages. These findings were consistent with the results of mixed labeling immunohistology showing that early in infection the expression of parasite antigen in the LN draining the lesion was confined to dendritic cells and could not be detected in macrophages. Furthermore, dendritic cells in LN draining the site of cutaneous infection stimulated L. major-primed T cells in vitro and, most notably, were able to activate unprimed T cells capable of mediating parasite-specific delayed-type hypersensitivity reactivity in vivo. Taken together, the results indicate that LC capture L. major in the skin and transport it to the regional LN for initiation of the specific T cell immune response.