Leishmania major-infected murine Langerhans cell-like dendritic cells from susceptible mice release IL-12 after infection and vaccinate against experimental cutaneous Leishmaniasis

Leishmania major-infected C57BL/6 skin-dendritic cells (DC) are activated and release cytokines (including IL-12 p70), and likely initiate protective Th1 immunity in vivo (von Stebut, E. et al., J. Exp. Med. 188: 1547-1552). To characterize differences in DC function in mice that are genetically susceptible (BALB/c) and resistant (C57BL/6) to cutaneous leishmaniasis, we analyzed the effects of L. major on Langerhans cell-like, fetal skin-derived DC (FSDDC) from both strains. BALB/c- and C57BL/6-FSDDC ingested similar numbers of amastigotes, but did not ingest metacyclic promastigotes. Like C57BL/6-FSDDC, infection of BALB/c-FSDDC led to up-regulation of MHC class I and II antigens, CD40, CD54, and CD86 within 18 h. L. major-induced BALB/c DC activation also led to the release of TNF-α, IL-6 and IL-12 p40 into 18-h supernatants. Infected BALB/c- and C57BL/6-DC both released small amounts of IL-12 p70 within 72 h. Additional stimulation with IFN-γ and/or anti-CD40 induced the release of more IL-12 p70 from infected BALB/c-DC than C57BL/6-DC. Coculture of control or infected BALB/c- and C57BL/6-DC with naive syngeneic CD4⁺ T cells and soluble anti-CD3 resulted in mixed, IFN-γ-predominant responses after restimulation with immobilized anti-CD3. Finally, syngeneic L. major-infected DC effectively vaccinated BALB/c mice against cutaneous leishmaniasis. Genetic susceptibility to L. major that results from induction of Th2 predominant immune responses after infection does not appear to reflect failure of skin DC to internalize or respond to parasites, or the inability of BALB/c T cells to mount a Th1 response to DC-associated Leishmania antigens.