Since IL-10 secretion by CD4+ CD25+ FoxP3+ Treg cells [27], [28], [39] as well as CD4+ CD25− FoxP3− Th1 cells [29], [30], [40] has been implicated in the control of chronic infection with Leishmania, it was important to determine the T cell population secreting IL-10 early after infection. This evidence concerns the gene IL10 and infection.