To determine whether a population of CD4+CD38hi cells is present in individuals undergoing secondary exposure to Plasmodium, similar to individuals undergoing primary exposure8, we performed flow cytometric assessment of CD38 expression on CD4+ T cells from PBMCs collected from Malaysian and Indonesian adults who presented to hospitals with acute uncomplicated P. falciparum malaria or P. knowlesi malaria (before the commencement of drug treatment: acute, day 0) (subject details in Table 1). The gene discussed is CD38; the disease is malaria.