IL6 and infection: In order to assess whether lack of cutaneous IL-6 production would impair development of Th1 cells, we demonstrated that IL-6 −/− mice with IL-6 competent bone marrow and thus with a constitutional lack of IL-6 at the site of infection, became markedly more susceptible to L. major (more than 1000 fold more parasites compared to control animals) and showed a shift from a Th1 towards a Th2 response.