Knowledge about thediverse immune cells involved in host responseagainst Leishmania infection has accrued from anearly, still highly relevant view4 of cross-talkbetween Th1 and Th2 CD4+ subsets with the macrophage tothe realization that Leishmania-triggered responsesencompass not only new CD4+ subtypes but also the recruitmentof CD8+, natural killer cells, basophils, neutrophils,and eosinophils,5−7 each with different roles depending on the time andclinical form of leishmaniasis. The gene discussed is CD4; the disease is leishmaniasis.