CD4 and malaria: To investigate whether P. falciparum antigens can induce Treg cells in vitro, peripheral blood mononuclear cells (PBMCs) from five healthy malaria-naïve donors, each assayed twice, were cultured for 7 days with growth medium (GM), uninfected red blood cells (uRBCs), or P. falciparum schizont extract (PfSE) and the percentage of CD4+ cells expressing a Treg-cell (FOXP3+CD127lo/−) or Teff-cell phenotype (defined as CD4+CD25+FOXP3− cells) was determined ex vivo, and on days 2, 3, 4, 5, 6, and 7 by flow cyto-metry (Fig. 1A and B).