Cross-talk between CD8(+) and CD4(+) T cells in experimental cutaneous leishmaniasis: CD8(+) T cells are required for optimal IFN-gamma production by CD4(+) T cells.

Although the importance of CD8(+) T cells for vaccination and immunity to reinfection with Leishmania parasites is well established, their role in primary infections is disputed. In the present study we further characterized the role of CD8(+) T cells in primary L. major infections. We used two groups of L. major infected BALB/c mice: both groups were immunomanipulated to heal and in one group CD8(+) T cells were depleted throughout the course of infection. Our results show that the reversal of healing caused by the absence of CD8(+) T cells did not alter the proliferation of CD4(+) T cells, however, the frequency of CD4(+) T cells expressing IFN-gamma as well as the levels of this cytokine were clearly reduced. These lower levels of IFN-gamma correlated with a higher parasite load. Our results show that transient depletion of CD4(+) T cells allows the establishment of an equilibrium between CD4(+) and CD8(+) T cells and allows CD8(+) T cell activation and effector functions to develop. In addition, our results suggest that cross-talk between CD4(+) and CD8(+) T cells is crucial for the host defence against L. major.