Early Phagocytosis of Glucose-6-Phosphate Dehydrogenase (G6PD)-Deficient Erythrocytes Parasitized by Plasmodium falciparum May Explain Malaria Protection in G6PD Deficiency

Abstract

In population-based studies it has been established that inherited deficiency of erythrocyte (E) glucose-6-phosphate dehydrogenase (G6PD) confers protection against severe Plasmodium falciparum (P falciparum) malaria. Impaired growth of parasites in G6PD-deficient E in vitro has been reported in some studies, but not in others. In a systematic analysis, we have found that with five different strains ofP falciparum (FCR-3, KI, C10, HB3B, and T9/96), there was no significant difference in either invasion or maturation when the parasites were grown in either normal or G6PD-deficient (Mediterranean variant) E. With all of these strains and at different maturation stages, we were unable to detect any difference in the amount of P falciparum–specific G6PD mRNA in normal versus deficient parasitized E. The rate of 14C-CO2 production from D-[1-14C] glucose (which closely reflects intracellular activity of G6PD) contributed by the parasite was very similar in intact normal and deficient E. By contrast, in studies of phagocytosis of parasitized E by human adherent monocytes, we found that when the parasites were at the ring stage (ring-stage parasitized E [RPE]), deficient RPE were phagocytosed 2.3 times more intensely than normal RPE (P = .001), whereas there was no difference when the parasites were at the more mature trophozoite stage (trophozoite-stage parasitized E [TPE]). Phagocytic removal markers (autologous IgG and complement C3 fragments) were significantly higher in deficient RPE than in normal RPE, while they were very similar in normal and deficient TPE. The level of reduced glutathione was remarkably lower in deficient RPE compared with normal RPE. We conclude that impaired antioxidant defense in deficient RPE may be responsible for membrane damage followed by phagocytosis. Because RPE, unlike TPE, are nontoxic to phagocytes, the increased removal by phagocytosis of RPE would reduce maturation to TPE and to schizonts and may be a highly efficient mechanism of malaria resistance in deficient subjects.

Genetic variation and susceptibility to infection: the red cell and malaria

“…It is still not absolutely clear how G6PD deficiency protects against malaria. It is very likely that it is related to the susceptibility of G6PD-deficient red cells to oxidative stress; the observation that deficient red cells undergo phagocytosis by macrophages at an earlier stage than parasitised normal cells (Cappadoro et al, 1998) raises the possibility that, rather as has been suggested for the protective effect mediated by the sicklecell variant, suicidal infection may be at least one protective mechanism (Luzzatto et al, 2001).…”

Erythrocyte variants and the nature of their malaria protective effect

“…Under conditions of oxidative stress, which can cause major haemolysis in G6PD-deficient individuals, growth of Plasmodium seems to be inhibited more consistently (Miller et al, 1984;Golenser et al, 1988). Recent studies by Cappadoro et al (Cappadoro et al, 1998) have shown that G6PD-deficient erythrocytes were more susceptible to phagocytosis by peripheral blood monocytes, particularly at the early ring-stage of infection concomitant to increased binding of IgG and complement C3 to infected erythrocytes. G6PD-deficient cells are more prone to changes in the cell membrane because of low levels of GSH (see Fig.…”

“…Importantly, the reduced life-span and early removal from the circulation of PK-deficient erythrocytes may, as proposed for haemoglobinopathies and for G6PD deficiency, also result in increased phagocytosis of parasitized red cells early in infection. Whether this is mediated by increased expression of phagocytic markers like complement C3 and IgG, as seems to be the case for alphathalassaemia and G6PD deficiency (Cappadoro et al, 1998;Ayi et al, 2004), remains to be tested.…”

Blood oxidative stress markers and Plasmodium falciparum malaria in non‐immune African children

“…Mechanistically, the increased membrane-bound Hb levels may contribute to a more efficient clearing of parasitized RBCs from the circulation, reducing the incidence of clinical malaria. Constitutively increased levels of membrane-bound Hb may be due to malaria-protective mutations (Cappadoro et al, 1998;Ayi et al, 2004) and persistence of Hb F (Advani et al, 1992;Amaratunga et al, 2011). The increased membrane-bound Hb might be also the mechanistic link for the herein observed positive association between GSH level in the RBC and malaria IR.…”

“…A second set of data investigates the shown in vitro generation of oxidative stress exerted by the growing parasite to the RBC membrane (Atamna & Ginsburg, 1993;Skorokhod et al, 2007), oxidizing Hb and producing intracellular membrane-bound haemichromes (Rifkind et al, 1994;Giribaldi et al, 2001;Arese et al, 2005) that cluster band 3, leading to opsonization and phagocytosis of the RBC (Giribaldi et al, 2001;Arese et al, 2005;Pantaleo et al, 2008). The enhanced phagocytosis observed in ring-parasitized RBCs with the sickle-cell trait, glucose-6-phosphate dehydrogenase-deficiency or the thalassaemias, has been proposed as the mechanism underlying the protective effect of those mutations (Cappadoro et al, 1998;Ayi et al, 2004). Similarly, the increased Hb-binding observed in oxidized RBC membranes (Demehin et al, 2001) might add to this mechanism, triggered by reactive oxygen species from activated phagocytes and parasites, unstable Hb or free haem.…”