Tese de Doutoramento Ciências da Saúde 2024 Faculdade de Ciências Médicas, Universidade NOVA de Lisboa

Severe malarial anemia is a complication that develops during Plasmodium infection, increasing the risk of morbidity and mortality. It is caused by a dysregulated immune response, which triggers an unbalanced release of inflammatory mediators impacting, ultimately, the production of red blood cells. In view of the interplay existing between inflammation and iron metabolism, this study examined the influence of the disruption of iron homeostasis in malaria-induced anemia. Emphasis was given to the role of the hereditary hemochromatosis protein HFE, a known iron sensor, and its ability to regulate the host immune response to malaria infection. To this end, we used a loss of function approach, performing experiments in HFE-deficient mice and comparing the results to wild-type controls. Animals were infected with Plasmodium chabaudi chabaudi (Pcc), this being the parasite used to induce severe forms of malaria and to study the disruption of iron homeostasis in view of the pronounced degree of hemolysis it causes in mice. When infected, HFE-knockout animals enhance erythropoiesis in the bone marrow and reduces stress erythropoiesis in the spleen. Hence, an improvement of the anemic profile was detected in HFE-deleted animals in relation to wild-type mice, upon Pcc infection. An early cell-mediated immune response is required to control malaria and reduce its associated symptomatology. CD4+ T cells are essential to prevent uncontrolled parasite growth, while a humoral response is necessary to inhibit recrudescence and to clear the infection. Given the resemblance of HFE to MHC class I, a molecule responsible for CD8+ T cell activation, we investigated whether HFE deficiency would enhance the CD4+/B cell axis. Our results showed an expansion of CD4+ and B lymphocytes, upon infection, and a decrease in CD8+ T cells in the bone marrow. An improved innate immune response was also observed in HFE-knockout mice. The reduced hepcidin production was shown to prevent granulocytes from undergoing iron cytotoxicity, in bone marrow and spleen. Specifically, a decrease in iron uptake was detected in monocytes and neutrophils, which populations presented high counts in HFE-deficient mice in relation wild-type controls, upon Pcc infection. When compared to wild-type animals, HFE-deficient mice showed lower parasitemia, in agreement with findings previously described. Children under 5 years of age, living in endemic areas, are at high risk for reinfection. Therefore, HFE deficient mice were also re-exposed to the same Plasmodium strain. The erythropoietic response was found to be improved and the concentration of plasma erythropoietin decreased, when compared to reinfected wild-type controls. In addition, reinfected HFE-knockout animals showed a higher production of memory CD4+ and CD8+ T cells, which are potentially linked to an upregulation of GM-CSF, known to promote the activation, proliferation, and differentiation of T cells. The result is a long-term immunity observed in HFE-deficient mice, upon reinfection. Hence, this study suggests that mutations involved in iron sensing, such as HFE, and linked to condition of iron overload might afford protection against iron-related infections, like malaria. By providing an evolutionary advantage, HFE could serve as potential target for drug therapy against this hemolytic disorder