Stage-specific susceptibility of human erythroblasts to Plasmodium falciparum malaria infection

Abstract

Malaria parasites are known to invade and develop in erythrocytes and reticulocytes, but little is known about their infection of nucleated erythroid precursors. We used an in vitro cell system that progressed through basophilic, polychromatic, orthochromatic, and reticulocyte stages to mature erythrocytes. We show that orthochromatic cells are the earliest stages that may be invaded by Plasmodium falciparum, the causative agent of fatal human malaria. Susceptibility to invasion is distinct from intracellular survival and occurs at a time of extensive erythroid remodeling. Together these data suggest that the potential for complexity of host interactions involved in infection may be vastly greater than hitherto realized. ( IntroductionApproximately 40% of the world's population is at risk of developing malaria, 1 which is caused by infections of the human malaria parasites Plasmodium falciparum and Plasmodium vivax. During blood-stage infection, which causes all symptoms and pathologies of malaria, the parasite infects mature erythrocytes and reticulocytes. Isolated reports suggest that nucleated erythroid progenitors may also be infected, 2,3 but little is known of when in maturation they become susceptible and the complexity of associated cellular remodeling events. There is considerable interest in these parameters, because they underlie host interactions with a major human pathogen that is thought to have profoundly influenced erythroid development. 4 We have used an in vitro model system using primary cells to study commitment to the erythroid lineage and differentiation of committed progenitors to reticulocytes. 5,6 The advantages are that the kinetics of differentiation in vitro closely resembles that of erythroid cell maturation in the bone marrow, and differentiation occurs in a relatively synchronous manner. In this system we examine malarial infection during complex, cellular remodeling at terminal steps of erythroid differentiation. We show that despite prior reports, 3 only orthochromatic erythroblasts can be infected by falciparum malaria and that the process of infection is functionally segregated into 2 categories: early-mid orthochromatic erythroblasts can support parasite invasion, but only late orthochromatic/ nascent reticulocytes sustain intracellular parasite growth. Methods Primary human erythroid cultures and flow cytometryHuman primary erythroblasts were generated by culturing CD34 ϩ early hematopoietic progenitors initially isolated from growth factor-mobilized peripheral blood (purchased from ALL Cells Inc). Culture and subsequent flow cytometry sorting of cultured cells were carried out as previously described. 5 On day 7 of culture, erythroid cells positive for the transferrin receptor (CD71) were purified to 98% to 99% using a MoFlo high-speed flow cytometer (BD Biosciences). Sorted cells were subsequently cultured (in day 8 media formulation) and fed once more on day 10 with media containing only erythropoietin (2 units/mL). Parasite infectionP falciparum 3D7 was synchronized by s...

Biology of Malaria Transmission

“…In agreement with this hypothesis, in vitro data indicates an enhanced invasion of erythroid progenitor cells with a concomitant increase in gametocyte formation within young RBCs (Tamez et al 2009;Peatey et al 2013). More focused studies are required to decipher the mechanism of gametocyte sequestration, including identification of parasite stages that home to the bone marrow, the receptor-ligand interactions involved, if any, and importantly, whether sexual commitment occurs in the periphery or in the bone marrow microenvironment.…”

Malaria and haematologic parameters of pupils at different altitudes along the slope of Mount Cameroon: a cross-sectional study

“…The severity of haematologic disease caused by Plasmodium is related to the ability of the parasites to invade and grow in different red cell populations as well as the intrinsic growth rate of the parasite [4]. Anaemia is consequently an inevitable outcome of malaria infection, but the haematocrit (Hct) in some patients with high parasite densities does not decrease as much as would be expected from the destruction of the parasitized red blood cells [5].…”

Application of genomics to field investigations of malaria by the international centers of excellence for malaria research

“…Although methods for P. falciparum culturing have been available for some time (Trager and Jensen, 1976), culture systems for P. vivax have proved more challenging. Renewed efforts to develop such a culture system leverage stem cells to produce the required reticulocytes for supporting P. vivax growth in culture (Bei et al, 2010; Giarratana et al, 2005; Panichakul et al, 2007; Tamez et al, 2009). An additional concern is the consequence of the culture adaptation process on the selection of either specific parasite types that survive (Nsobya et al, 2008), or possibly the alteration of the genomic composition of the parasite during the adaptation process (Pologe and Ravetch, 1988).…”