Host Reticulocyte Redox Attenuation Creates a Protective Niche for Artemisinin Tolerance in Plasmodium falciparum

Artemisinin-based combination therapies are the cornerstone of Plasmodium falciparum malaria treatment; however, delayed parasite clearance and treatment failure occur even in the absence of established parasite genetic resistance. While parasite-intrinsic resistance mechanisms have been extensively studied, the contribution of host erythroid heterogeneity to antimalarial drug response remains poorly defined.

Highly purified human CD71+ve reticulocytes and mature erythrocytes were used to assess parasite invasion, intraerythrocytic development, and drug susceptibility. Integrated metabolomic and proteomic analyses characterized host cell environments. Parasite responses to artemisinin derivatives and antimalarials with distinct mechanisms of action were systematically evaluated.

P. falciparum preferentially invaded reticulocytes and exhibited accelerated asexual development within these cells. Multi-omics analyses demonstrated that reticulocytes provide a metabolically enriched, antioxidant-modulated intracellular environment, marked by increased nucleotide precursors, enhanced glutathione metabolism, and elevated levels of reactive oxygen species (ROS)-detoxifying enzymes. Parasites developing within reticulocytes showed significantly reduced susceptibility to artemisinin and dihydroartemisinin, as well as to other redox-active antimalarials, while maintaining comparable sensitivity to drugs with non-oxidative mechanisms. Reticulocyte-resident parasites also demonstrated enhanced survival and recrudescence following artemisinin exposure.

Erythroid maturation state is a key host determinant of antimalarial drug efficacy. Reticulocytes form a redox-protected intracellular niche that attenuates drug-induced oxidative stress and promotes parasite persistence, consistent with a host cell-mediated tolerance phenotype. These findings provide a mechanistic framework for variability in treatment outcomes associated with reticulocytosis and anemia.