Immunopathology of leishmaniasis: An update

Leishmaniasis represents a severe, increasing, public health problem. The perspective of its control is highly dependent on research progress, on therapeutic manipulations of the immune system, and on vaccine development. There is a correlation between the clinical outcome of Leishmania infection and the cytokine response profile. While a protective immune response against Leishmania has been clearly identified to be related to the influence of a type-1 response and IFN-gamma production, the precise role of T helper (T-H) 2 cytokines in non-healing infections requires further exploration. IL-4 and IL-13 (T-H 2 cytokines) can promote disease progression in cutaneous leishmaniasis, whereas IL-4 would appear to enhance protective type-1 responses in visceral leishmaniasis. Thus, the T(H)1/T(H)2 paradigm of resistance/ susceptibility to intracellular parasites is probably an oversimplification of a more complicated network of regulatory/counter regulatory interactions. Moreover, the presence of antigen specific regulatory T cell subsets may provide an environment that contributes to the balance between T(H)1 and T(H)2 cells. Finally, the involvement of CD8(+) T cells has been described, but the modality of their function in this kind of infection has not been so far elucidated.