ABSTRACTLack of an adequate animal model ofPlasmodium falciparumsevere malarial anemia (SMA) has hampered the understanding of this highly lethal condition. We developed a model of SMA by infecting C57BL/6 mice withP. chabaudifollowed after recovery byP. bergheiinfection.P. chabaudi/P. berghei-infected mice had an initial 9- to 10-day phase of relatively low parasitemia and severe anemia, followed by a second phase of hyperparasitemia, more profound anemia, reticulocytosis, and death 14 to 21 days after infection.P. chabaudi/P. berghei-infected animals had more intense splenic hematopoiesis, higher interleukin-10 (IL-10)/tumor necrosis factor alpha and IL-12/gamma interferon (IFN-γ) ratios, and higher antibody levels againstP. bergheiandP. chabaudiantigens thanP. berghei-infected orP. chabaudi-recovered animals. Early treatment with chloroquine or artesunate did not prevent the anemia, suggesting that the bulk of red cell destruction was not due to the parasite. Red cells fromP. chabaudi/P. berghei-infected animals had increased surface IgG and C3 by flow cytometry. However, C3−/−mice still developed anemia. Tracking of red cells labeledex vivoandin vivoand analysis of frozen tissue sections by immunofluorescence microscopy showed that red cells fromP. chabaudi/P. berghei-infected animals were removed at an accelerated rate in the liver by erythrophagocytosis. This model is practical and reproducible, and its similarities withP. falciparumSMA in humans makes it an appealing system with which to study the pathogenesis of this condition and explore potential immunomodulatory interventions.

Malaria, a disease caused by an intracellular parasite of the genus Plasmodium, causes 350-500 million cases annually with 1-2 million deaths. The majority of these deaths occur in children in sub-Saharan Africa due to complications of P. falciparum infection, such as severe malarial anemia (SMA). The pathogenesis of SMA is complex and not well understood; however, it is known that there is greater destruction of red cells The first model we utilized was a well established model of malarial anemia involving the rodent parasite P. chabaudi in C57BL/6 mice. We ascertained that Crry partial deficiency did not result in more severe anemia evident by blood counts, but did result in a higher level of erythrophagocytosis which could be negated with supplementation of the deficient protein. These findings indicate that Crry is important in red cell protection during a malaria infection. Since Crry, whose function is to protect host cells from complement attack, is important in red cell protection during a malaria infection, does that necessarily mean C3 is deleterious and/or causes more severe anemia? Our results in C3 deficient animals suggest that it may be harmful since C3 deficient animals had less severe anemia; however, these animals still developed anemia and were able to clear and sequester transferred red cells.In order to study SMA in a model more representative of P. falciparum infection, we developed the second model that was used to investigate SMA pathogenesis. We showed that P. berghei infection following recovery from P. chabaudi infection in C57BL/6 animals resulted in anemia with a low level parasitemia. Characterization of the model revealed similarities to anemia in P. chabaudi infected animals, such as increased organ pathology and erythrophagocytosis. This model can now be used to evaluate factors such as complement and complement regulatory proteins in the development of anemia.v