Interferon-gamma is required for the late but not early control of Leishmania amazonensis infection in C57Bl/6 mice

The critical role of interferon-gamma (IFN-γ) in the resistance of C57Bl/6 mice to Leishmania major is widely established but its role in the relative resistance of these animals to L. amazonensis infection is still not clear. In this work we use C57Bl/6 mice congenitally deficient in the IFN-γ gene (IFN-γ KO) to address this issue. We found that IFN-γ KO mice were as resistant as their wild-type (WT) counterparts at least during the first two months of infection. Afterwards, whereas WT mice maintained lesion growth under control, IFN-γ KO mice developed devastating lesions. At day 97 of infection, their lesions were 9-fold larger than WT controls, concomitant with an increased parasite burden. At this stage, lesion-draining cells from IFN-γ KO mice had impaired capacity to produce interleukin-12 (IL-12) and tumour necrosis factor - α in response to parasite antigens whereas IL-4 was slightly increased in comparison to infected WT mice. Together, these results show that IFN-γ is not critical for the initial control of L. amazonensis infection in C57Bl/6 mice, but is essencial for the developmente of a protective Th1 type immune response in the later stages.