In African trypanosomiasis, the expansion of Treg cells seems to occur from the parasite establishment to the chronic stage, being associated with parasite tolerance (reviewed in [29]) and in trypanotolerant C57BL/6 mice, the expansion of CD25+ FoxP3+ CD4+ T cell subset was demonstrated after the first peak of parasitemia [30]. The gene discussed is CD4; the disease is human African trypanosomiasis.