Signatures of divergent antimalarial treatment responses in peripheral blood from infants and adults in Malawi

Background: Heterogeneity in the immune response to parasite infection is mediated in part by differences in host genetics, sex, and age group. In neonates and infants, ongoing immunological maturation often results in increased susceptibility to infection and variable responses to drug treatment, increasing the risk of complications. Even though significant age-specific effects on host cytokine responses to Plasmodium falciparum infection have been identified, age effects on uncomplicated malaria infection and antimalarial treatment remain poorly understood. Methods: In samples of whole blood from a cohort of naturally infected malaria-positive individuals in Malawi (n=63 total; 34 infants 18 years old), we assessed blood cytokine levels and characterized monocyte and dendritic cell frequencies at two timepoints: acute infection, and four weeks post antimalarial treatment. We modeled the effects of age group, sex, and timepoint, and evaluated the role of these factors on infection and treatment outcomes. Results: Regardless of treatment timepoint, in our population age was significantly associated with overall blood hemoglobin, which was higher in adults, and plasma nitric oxide, IL-10, and TNF-α levels, which were higher in infants. We found a significant effect of age on the hemoglobin treatment response, whereby after treatment, levels increased in infants and decreased in adults. Furthermore, we observed significant age-specific effects on treatment response for overall parasite load, IFN-γ, and IL-12(p40), and these effects were sex-dependent. We uncovered significant age effects on the overall levels and treatment response of myeloid dendritic cell frequencies. In addition, within each age group, we found continuous age effects on gametocyte levels (Pfs16), TNF-α, and nitric oxide. Conclusions: In a clinical study of infants and adults experiencing natural malaria infection and receiving antimalarial treatment, we identified age-specific signatures of infection and treatment responses in peripheral blood. We describe host markers that may indicate, and potentially mediate, differential post-treatment outcomes for malaria in infants versus adults.