Up to 200 children will be recruited into longitudinal studies that will be conducted in Ouelessebougou and neighboring villages in Mali. In August 2015, up to 50 children presenting for Seasonal Malaria Chemoprevention (SMC) in a village where the government has implemented SMC will be enrolled, as well as up to 50 age-matched children residing in an adjacent village where SMC has not been implemented by the government of Mali; and then followed through the rainy season. In January 2016, up to 100 healthy children in Ouelessebougou village area will be enrolled and randomized to receive or not receive a course of artemether-lumefantrine, and then followed for the duration of the dry season (Jan-Jun 2016) and the subsequent rainy season (Jul-Dec 2016). Samples in both cohort studies (age-matched SMC study; randomized artemether-lumefantrine study) will be collected from the children at the time of monthly visits and assessed in ex vivo assays for markers of T cell suppression as the primary outcome of this study. For our secondary outcomes, we will examine levels of regulatory T cells, measure T cell responses in stimulation assays, and survey parasitemia by blood smear and by polymerase chain reaction (PCR) assays. We expect that levels of T cell suppression and regulatory T cells will be similar between groups before antimalarial treatment or malaria infection, but after treatment or in those subjects that remain uninfected these levels will be significantly lower as compared to the untreated and or infected subjects.