Preserved Dendritic Cell HLA-DR Expression and Reduced Regulatory T Cell Activation in Asymptomatic Plasmodium falciparum and P. vivax Infection

Clinical illness with Plasmodium falciparum or Plasmodium vivax compromises the function of dendritic cells (DC) and ex-pands regulatory T (Treg) cells. Individuals with asymptomatic parasitemia have clinical immunity, restricting parasite expan-sion and preventing clinical disease. The role of DC and Treg cells during asymptomatic Plasmodium infection is unclear. Dur-ing a cross-sectional household survey in Papua, Indonesia, we examined the number and activation of blood plasmacytoid DC (pDC), CD141, and CD1cmyeloid DC (mDC) subsets and Treg cells using flow cytometry in 168 afebrile children (of whom 15 had P. falciparum and 36 had P. vivax infections) and 162 afebrile adults (of whom 20 had P. falciparum and 20 had P. vivax infections), alongside samples from 16 patients hospitalized with uncomplicated malaria. Unlike DC frommalaria patients, DC from children and adults with asymptomatic, microscopy-positive P. vivax or P. falciparum infection increased or retained HLA-DR expression. Treg cells in asymptomatic adults and children exhibited reduced activation, suggesting increased immune responsiveness. The pDC andmDC subsets varied according to clinical immunity (asymptomatic or symptomatic Plasmodium infection) and, in asymptomatic infection, according to host age and parasite species. In conclusion, active control of asymptom