Further, it should be noted that, prior to recognition of regulatory T cells, IL-2 was shown to be necessary for disease progression during experimental L. major infection of susceptible murine hosts [25], [47], [48] (although the effects of IL-2 manipulation on the course of experimental infection with L. donovani appears to be more complicated, suggesting the need for caution in extrapolating these findings to visceral leishmaniasis [49], [50]). This evidence concerns the gene IL2 and visceral leishmaniasis.