BALB/c mice are genetically susceptible to infection with Leishmania major (L. major). When such mice infected with L. major were treated with specific inhibitors of cathepsin B, a lysosomal cysteine protease that digests exogenous antigenic proteins, the mice acquired resistance against L. major infection. T cells from these mice produced large amounts of IFN-γ and low amounts of IL-4 as compared with those of untreated BALB/c mice. In addition, the mice treated with cathepsin B inhibitor produced a high titer of IgG2a specific antibodies and only low titers of IgG1 and IgE antibodies. This type of response is in contrast with the high specific IgG1 or IgE antibody responses which are the usual antibody responses in BALB/c mice infected with L. major. These findings indicate that cathepsin B may be critically involved in processing antigens of L. major to promote exclusively the development of Th2 type CD4+T cell responses
