In both P. yoeliiyoelii 17XNL infection and in falciparum malaria, IL-2 is necessary for the expansion of CD25Foxp3 CD4+ T cells (T regulatory cells, or Tregs) (79, 80) and for activating natural killer (NK) cells, which function in the lysis of infected erythrocytes (79, –, 81). The gene discussed is CD4; the disease is Plasmodium falciparum malaria.