Examining the Reticulocyte Preference of Two Plasmodium berghei Strains during Blood-Stage Malaria Infection

Abstract

The blood-stage of the Plasmodium parasite is one of the key phases within its life cycle that influences disease progression during a malaria infection. The efficiency of the parasite in infecting red blood cells (RBC) determines parasite load and parasite-induced hemolysis that is responsible for the development of anemia and potentially drives severe disease progression. However, the molecular factors defining the infectivity of Plasmodium parasites have not been completely identified so far. Using the Plasmodium berghei mouse model for malaria, we characterized and compared the blood-stage infection dynamics of PbANKA WT and a mutant parasite strain lacking a novel Plasmodium antigen, PbmaLS_05, that is well conserved in both human and animal Plasmodium parasite strains. Infection of mice with parasites lacking PbmaLS_05 leads to lower parasitemia levels and less severe disease progression in contrast to mice infected with the wildtype PbANKA strain. To specifically determine the effect of deleting PbmaLS_05 on parasite infectivity we developed a mathematical model describing erythropoiesis and malarial infection of RBC. By applying our model to experimental data studying infection dynamics under normal and drug-induced altered erythropoietic conditions, we found that both PbANKA and PbmaLS_05 (-) parasite strains differed in their infectivity potential during the early intra-erythrocytic stage of infection. Parasites lacking PbmaLS_05 showed a decreased ability to infect RBC, and immature reticulocytes in particular that are usually a preferential target of the parasite. These altered infectivity characteristics limit parasite burden and affect disease progression. Our integrative analysis combining mathematical models and experimental data suggests that deletion of PbmaLS_05 affects productive infection of reticulocytes, which makes this antigen a useful target to analyze the actual processes relating RBC preferences to the development of severe disease outcomes in malaria.

Rodent Malaria Erythrocyte Preference Assessment by an Ex Vivo Tropism Assay

“…Therefore, using flow cytometry to objectively define the erythrocyte populations, we performed comprehensive in vivo tropism measurements for the major rodent malaria strains. Our results broadly agree with previous observations: PbA and Py1.1 have a strong reticulocyte preference ( Fahey and Spitalny, 1984 ; Deharo et al., 1996 ; Cromer et al., 2006 ; Otsuki et al., 2009 ; Martín-Jaular et al., 2013 ; Thakre et al., 2018 ), PccAS has a mixed tropism ( Jarra and Brown, 1989 ), and PvvS67 has a slight normocyte tropism ( Viens et al., 1971 ; Vigário et al., 2001 ). An important distinction between the present study and those before is that we only strictly compared normocytes with the earliest stages of reticulocytes (which still retain many surface proteins).…”

“…Microscopic evaluations are also subjective, and this problem is compounded by the difficulty of differentiating late-stage parasites in reticulocytes from those in normocytes. More recent tropism studies used flow cytometry to distinguish erythrocyte types by their levels of CD71 expression, but these are constrained to only certain species, like P. berghei ( Dertinger et al., 2000 ; Thakre et al., 2018 ).…”

A Plasmodium Cross-Stage Antigen Contributes to the Development of Experimental Cerebral Malaria

“…To determine if the growth defect of PbmaLS_05 (−) parasites was due to reduced multiplication rates, we analyzed the parasite growth kinetics in KO-iRBC-infected mice, through a mathematical model. Interestingly, the model suggested that deletion of PbmaLS_05 had a modest effect on the ability of parasites to develop within reticulocytes during the initial stages of infection ( 82 ). Therefore, it is plausible that a minor population of KO parasites that fail to develop within reticulocytes are cleared by the spleen and elicit an immune response that protects against ECM.…”

Within‐host modeling of blood‐stage malaria

“…Other species such as P. falciparum are thought to target all RBCs equally, although there is evidence for preferential invasion of a subset of cells, especially reticulocytes . A number of models that incorporate more sophisticated details of RBC (reticulocyte) production, and preferential targeting of certain RBC stages have been constructed (eg, Figure ; ). These studies have, in most cases, adopted a structure similar to either the many compartment ODE or the PDE models in Figure , but to capture the age structure of the RBCs rather than the parasites (illustrative model presented in Figure ).…”