Both Leishmania major and L. braziliensis induce cutaneous
leishmaniasis in BALB/c mice. Whereas BALB/c mice die of infection with L. major,
they cure an infection with L. braziliensis. We report here that after curing an infection
with L. braziliensis, BALB/c mice are resistant to challenge with L. major.
When challenged with L. major, L. braziliensis pre-treated BALB/c mice mounted a
delayed-type hypersensitivity response to L. major and produced high amounts of
interferon -γ (IFN-γ) but low amounts of interleukin-4. The IFN-γ produced
by the L. braziliensis pre-infected mice was involved in the protection seen against
L. major challenge since treating the mice with a neutralizing anti-IFN-γ abrogated the protection. This suggests that cross-reactive antigen epitopes exist between L. braziliensis and L. major and that
pre-infection with L. braziliensis primes BALB/c mice to epitopes on L. major
that can elicit a protective Th1 response to the parasite.