Apoptosis of non-parasitised red blood cells in Plasmodium yoelii malaria

Abstract

Recently, while studying erythrocytic apoptosis during Plasmodium yoelii infection, we observed an increase in the levels of non-parasitised red blood cell (nRBC) apoptosis, which could be related to malarial anaemia. Therefore, in the present study, we attempted to investigate whether nRBC apoptosis is associated with the peripheral RBC count, parasite load or immune response. To this end, BALB/c mice were infected with P. yoelii 17XL and nRBC apoptosis, number of peripheral RBCs, parasitaemia and plasmatic levels of cytokines, nitric oxide and anti-RBC antibodies were evaluated at the early and late stages of anaemia. The apoptosis of nRBCs increased at the late stage and was associated with parasitaemia, but not with the intensity of the immune response. The increased percentage of nRBC apoptosis that was observed when anaemia was accentuated was not related to a reduction in peripheral RBCs. We conclude that nRBC apoptosis in P. yoelii malaria appears to be induced in response to a high parasite load. Further studies on malaria models in which acute anaemia develops during low parasitaemia are needed to identify the potential pathogenic role of nRBC apoptosis.

Plasmodium falciparum , but not P. vivax , can induce erythrocytic apoptosis

“…It is remarkable that even when this patient was not considered in analysis, plasma from the P. falciparum patients significantly increased erythrocytic apoptosis in vitro (P. falciparum vs control, p < 0.01; P. falciparum vs P. vivax, p < 0.003; nonparametric Mann Whitney test). Similar to the plasma from P. falciparum patients, plasma from P. yoelii 17XL-infected BALB/c mice obtained at the stage of infection related to increased induction of nRBC apoptosis in vivo (late stage) [8], but not those obtained at a stage in which apoptotic nRBC was not significantly detected (early stage) [8], induced apoptosis in a high percentage (96%) of human normal RBC after 48 h of incubation (Figure 1), supporting the possibility of nRBC apoptosis induction during P. falciparum infection. However, it was not possible to statistically infer the relationship between parasite load and apoptotic levels during falciparum malaria, because the majority of P. falciparum patients presented similar parasitemia levels ( Table 1).…”

“…However, an increase in the levels of apoptotic nonparasitized RBC (nRBC) was further evidenced in P. yoelii infection, pointing to the putative role of erythrocytic apoptosis in the pathogenesis of malaria [8]. Since apoptotic nRBC has not yet been assessed in human malaria infections, the present study attempted to address this issue in Brazilian malarious patients.…”

“…Apoptotic nRBC was detected through flow cytometry using Syto 16 and annexin V-PE double staining, as performed in our previous studies with P. yoelii 17XL [5,8]. However, in contrast to experimental malaria, that significantly increased the levels of apoptotic nRBC both ex-vivo and after 24 h incubation, no significant alteration of nRBC apoptosis rates was detected in P. vivax patients (mean ± SD: ex vivo, 0.73 ± 0.31%; 24 h, 1.13 ± 0.57%) when compared with non-infected control individuals (ex vivo, 0.78 ± 0.27%; 24 h, 1.03 ± 0.41%) (p > 0.05; non-parametric Mann Whitney test).…”

“…A pool of plasma was tested in parallel, it was obtained from BALB/c mice either at early (4 day) or at late (7 day) stages of lethal P. yoelii 17XL infection [8], when mean parasitemias were, respectively, 25% and 76%, as estimated by counting the number of pRBC in thin blood smears. Plasmas from clinically healthy individuals living in Manaus and a pool of plasmas from non-infected BALB/c mice were also used as controls.…”

Evidencing the Role of Erythrocytic Apoptosis in Malarial Anemia

“…Our studies have shown that induction of apoptosis is not limited to parasitized RBCs (pRBCs) but also occurs in non-parasitized RBCs (nRBCs), pointing to an involvement of both pRBC and nRBC in the pathogenesis of malaria through deflagration of suicide processes (Totino et al, 2009, 2011, 2013, 2014). Thus, the present review covers evidence implicating erythrocytic apoptosis in the pathogenesis of severe anemia, a common complication of malaria that represents an important public health concern strongly related to mortality in children and pregnant women living in malaria-hyperendemic regions of sub-Saharan Africa (Schantz-Dunn and Nour, 2009; Muoneke et al, 2012).…”