ICOS and malaria: Using a co-culture system of malaria-infected red blood cells (iRBCs) and peripheral blood mononuclear cells from healthy individuals, we found that two populations of Foxp3hi and Foxp3int CD4+CD25hi T cells with a typical Treg phenotype (CTLA-4+, CD127low, CD39+, ICOS+, TNFRII+) were induced.