An in vitro model for infection with Leishmania major that mimics the immune response in mice.

By using a primary in vitro response specific for Leishmania major, normal T cells from resistant CBA/CaH-T6J and susceptible BALB/c mice commit to a Th1 and a Th2 response, respectively. Since commitment occurred, we measured the production of gamma interferon (IFN-gamma), interleukin-1 (IL-1), IL-2, IL-4, IL-5, IL-10, and IL-12, prostaglandin E2 (PGE2), transforming growth factor beta (TGF-beta), and nitric oxide in the first 7 days of the response to identify factors that are critical for Th1 and Th2 development. While cells from resistant CBA mice produced more IFN-gamma, IL-10, and nitric oxide, cells from susceptible BALB/c mice produced more IL-1alpha, IL-5, PGE2, and TGF-beta. Although substantial amounts of IL-12 were detected, IL-12 did not associate with either Th1 or Th2 development. We did not anticipate that cells from resistant CBA mice would make more IL-10 in vitro. However, this also occurred in vivo since CBA mice produced substantial amounts of IL-10 following infection with L. major. Moreover, adding anti-IL-10 to primary in vitro responses enhanced production of IFN-gamma and nitric oxide by cells from CBA and BALB/c mice. Therefore, IL-10 cannot be regarded as a cytokine that associates with susceptibility to infection with L. major. Finally, the data presented here suggest that a collection of factors that can be produced by accessory cells influence Th commitment (e.g., IL-1, PGE2, and TGF-beta favor Th2 development).