Sequestration Of Erythrocytes Research Articles

Iron and Malaria: Absorption, Efficacy and Safety

Febrile malaria and asymptomatic malaria parasitemia substantially decrease iron absorption in single-meal, stable isotope studies in women and children, but to date there is no evidence of decreased efficacy of iron-fortified foods in malaria-endemic regions. Without inadequate malarial surveillance or health care, giving iron supplements to children in areas of high transmission could increase morbidity and mortality. The most likely explanation is the appearance of non-transferrin-bound iron (NTBI) in the plasma. NTBI forms when the rate of iron influx into the plasma exceeds the rate of iron binding to transferrin. Two studies in women have reported substantially increased NTBI with the ingestion of iron supplements. Our studies confirm this, but found no significant increase in NTBI on consumption of iron-fortified food. It seems likely that the malarial parasite in hepatocytes can utilize NTBI, but it cannot do so in infected erythrocytes. NTBI however may increase the sequestration of parasite-infected erythrocytes in capillaries. Bacteremia is common in children with severe malaria and sequestration in villi capillaries could lead to a breaching of the intestinal barrier, allowing the passage of pathogenic bacteria into the systemic circulation. This is especially important as frequent high iron doses increase the number of pathogens in the intestine at the expense of the barrier bacteria.

The AMPKyl subunit plays an essential role in erythrocyte membrane elasticity, and its genetic inactivation induces splenomegaly and anemia

AMP-activated protein kinase (AMPK) is an αβγ heterotrimer conserved throughout evolution and important for energy sensing in all eukaryote cells. AMPK controls metabolism and various cellular events in response to both hormones and changes in cellular energy status. The γ subunit senses intracellular energy status through the competitive binding of AMP and ATP. We show here that targeted disruption of the mouse AMPKγ1 gene (Prkag1) causes regenerative hemolytic anemia by increasing the sequestration of abnormal erythrocytes. Prkag1(-/-) mice displayed splenomegaly and iron accumulation due to compensatory splenic erythropoiesis and erythrophagocytosis. Moreover, AMPKγ1-deficient erythrocytes were highly resistant to osmotic hemolysis and poorly deformable in response to increasing shear stress, consistent with greater membrane rigidity. No change in cytoskeletal protein composition was observed; however, the phosphorylation level of adducin, a protein promoting the binding of spectrin to actin, was higher in AMPKγ1-deficient erythrocytes. Together, these results demonstrate that AMPKγ1 subunit is required for the maintenance of erythrocyte membrane elasticity.

Functional and immunological characterization of the var2CSA-DBL5ɛ domain of a placental Plasmodium falciparum isolate

Pregnancy-associated malaria (PAM) arises from sequestration of Plasmodium falciparum-parasitized erythrocytes (PE) in the placenta, leading to chronic symptoms in the expectant mother and serious consequences for fetal development. Placental sequestration has been linked to binding of chondroitin sulphate A (CSA) by the var2CSA variant of PfEMP1 expressed on the PE surface, and a substantial body of evidence shows that the immune response to var2CSA gives an effective protection against PAM. We have expressed the var2CSA-DBL5ɛ domain, derived from a placental isolate from Senegal, as soluble product in Escherichia coli and have shown using different criteria that the recombinant protein is obtained with the native conformation. Using surface plasmon resonance techniques, we have examined binding of DBL5ɛ to placental chondroitin sulphate proteoglyan and CSA; however, the recombinant protein also binds to other sulphated oligosaccharides, with higher affinity in some cases, indicating that the single domain lacks the specificity for CSA shown by the complete extra-cellular region of var2CSA and placental parasites. Recombinant DBL5ɛ was specifically recognized by sera from malaria-exposed Senegalese women in a parity-dependent manner but by sera not from children or males from the same endemic region. Conversely, DBL5ɛ induced antibodies in mice that recognized placental isolates from Benin but not isolates from children. The presence of universal epitopes thus supports DBL5ɛ as an interesting component of var2CSA to be considered for vaccine development.

A Naphthoquinone Derivative Can Induce Anemia through Phosphatidylserine Exposure-Mediated Erythrophagocytosis

A naphthoquinone derivative, beta-lapachone (betaL; 3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b]pyran-5,6-dione), is receiving huge attention for its potent therapeutic effects against various diseases. However, during the preclinical safety evaluation, repeated oral treatment of betaL in rats induced anemia, i.e., a significantly decreased erythrocyte count. In this study, in an effort to elucidate the mechanism underlying the betaL-induced anemia, we investigated the effects of betaL on erythrocytes with freshly isolated human erythrocytes in vitro and rat in vivo. betaL did not induce erythrocyte hemolysis, indicating that direct hemotoxicity was not involved in betaL-associated anemia. Meanwhile, phosphatidylserine (PS) exposure along with spherocytic shape change and microvesicle generation, important factors in the facilitation of erythrophagocytosis, were increased significantly by betaL. The PS exposure on erythrocytes was from betaL-induced reactive oxygen species generation and subsequent depletion of reduced glutathione and protein thiol, which culminated in the modified activities of phospholipid translocases, i.e., inhibition of flippase and activation of scramblase. It is important to note that coincubation of macrophage with betaL-treated erythrocyte in vitro showed increased erythrophagocytosis, demonstrating that the removal of erythrocyte by macrophage can be facilitated by betaL-induced PS exposure. In good accordance with these in vitro results, after oral administration of betaL in rats, increased PS exposure and depletion of glutathione were observed along with enhanced splenic sequestration of erythrocytes. In conclusion, these results suggest that betaL-induced anemia might be mediated through the PS exposure and subsequent erythrophagocytosis, providing novel insight into the drug-induced anemia.

Plasmodium falciparum–infected erythrocytes induce NF-κB regulated inflammatory pathways in human cerebral endothelium

AbstractCerebral malaria is a severe multifactorial condition associated with the interaction of high numbers of infected erythrocytes to human brain endothelium without invasion into the brain. The result is coma and seizures with death in more than 20% of cases. Because the brain endothelium is at the interface of these processes, we investigated the global gene responses of human brain endothelium after the interaction with Plasmodium falciparum–infected erythrocytes with either high- or low-binding phenotypes. The most significantly up-regulated transcripts were found in gene ontology groups comprising the immune response, apoptosis and antiapoptosis, inflammatory response, cell-cell signaling, and signal transduction and nuclear factor κB (NF-κB) activation cascade. The proinflammatory NF-κB pathway was central to the regulation of the P falciparum–modulated endothelium transcriptome. The proinflammatory molecules, for example, CCL20, CXCL1, CXCL2, IL-6, and IL-8, were increased more than 100-fold, suggesting an important role of blood-brain barrier (BBB) endothelium in the innate defense during P falciparum–infected erythrocyte (Pf-IRBC) sequestration. However, some of these diffusible molecules could have reversible effects on brain tissue and thus on neurologic function. The inflammatory pathways were validated by direct measurement of proteins in brain endothelial supernatants. This study delineates the strong inflammatory component of human brain endothelium contributing to cerebral malaria.

Comparison of different methods for delayed post-mortem diagnosis of falciparum malaria

BackgroundBetween 10,000 and 12,000 cases of imported malaria are notified in the European Union each year. Despite an excellent health care system, fatalities do occur. In case of advanced autolysis, the post-mortem diagnostic is impaired. Quicker diagnosis could be achieved by using rapid diagnostic malaria tests.MethodsIn order to evaluate different methods for the post-mortem diagnosis of Plasmodium falciparum malaria in non-immunes, a study was performed on the basis of forensic autopsies of corpses examined at variable intervals after death in five cases of fatal malaria (with an interval of four hours to five days), and in 20 cases of deaths unrelated to malaria. Detection of parasite DNA by PCR and an immunochromatographic test (ICT) based upon the detection of P. falciparum histidine-rich protein 2 (PfHRP2) were compared with the results of microscopic examination of smears from cadaveric blood, histopathological findings, and autopsy results.ResultsIn all cases of fatal malaria, post-mortem findings were unsuspicious for the final diagnosis, and autoptic investigations, including histopathology, were only performed because of additional information by police officers and neighbours. Macroscopic findings during autopsy were unspecific. Histopathology confirmed sequestration of erythrocytes and pigment in macrophages in most organs in four patients (not evaluable in one patient due to autolysis). Microscopy of cadaveric blood smears revealed remnants of intraerythrocytic parasites, and was compromised or impossible due to autolysis in two cases. PCR and ICT performed with cadaveric blood were positive in all malaria patients and negative in all controls.ConclusionIn non-immune fatalities with unclear anamnesis, ICT can be recommended as a sensitive and specific tool for post-mortem malaria diagnosis, which is easier and faster than microscopy, and also applicable when microscopic examination is impossible due to autolysis. PCR is more expensive and time-consuming, but may be used as confirmatory test. In highly endemic areas where asymptomatic parasitaemia is common, confirmation of the diagnosis of malaria as the cause of death has to rely on histopathological findings.

Absence of Erythrocyte Sequestration and Lack of Multicopy Gene Family Expression in Plasmodium falciparum from a Splenectomized Malaria Patient

BackgroundTo avoid spleen-dependent killing mechanisms parasite-infected erythrocytes (IE) of Plasmodium falciparum malaria patients have the capacity to bind to endothelial receptors. This binding also known as sequestration, is mediated by parasite proteins, which are targeted to the erythrocyte surface. Candidate proteins are those encoded by P. falciparum multicopy gene families, such as var, rif, stevor or PfMC-2TM. However, a direct in vivo proof of IE sequestration and expression of multicopy gene families is still lacking. Here, we report on the analysis of IE from a black African immigrant, who received the diagnosis of a malignant lymphoproliferative disorder and subsequently underwent splenectomy. Three weeks after surgery, the patient experienced clinical falciparum malaria with high parasitemia and circulating developmental parasite stages usually sequestered to the vascular endothelium such as late trophozoites, schizonts or immature gametocytes.Methodology/Principal FindingsInitially, when isolated from the patient, the infected erythrocytes were incapable to bind to various endothelial receptors in vitro. Moreover, the parasites failed to express the multicopy gene families var, A-type rif and stevor but expression of B-type rif and PfMC-2TM genes were detected. In the course of in vitro cultivation, the parasites started to express all investigated multicopy gene families and concomitantly developed the ability to adhere to endothelial receptors such as CD36 and ICAM-1, respectively.Conclusion/SignificanceThis case strongly supports the hypothesis that parasite surface proteins such as PfEMP1, A-type RIFIN or STEVOR are involved in interactions of infected erythrocytes with endothelial receptors mediating sequestration of mature asexual and immature sexual stages of P. falciparum. In contrast, multicopy gene families coding for B-type RIFIN and PfMC-2TM proteins may not be involved in sequestration, as these genes were transcribed in infected but not sequestered erythrocytes.

Cerebral Malaria: A New Way Forward with Magnetic Resonance Imaging (MRI)

Magnetic resonance studies offer a new way through the impasse that now seems to block further progress in disentangling the pathogenesis and improving the treatment of cerebral malaria, a catastrophic neurologic complication of infection with Plasmodium falciparum. The underlying mechanisms responsible for coma in cerebral malaria are still unknown and the relative contributions of the microvascular sequestration of infected erythrocytes, the inflammatory response to P. falciparum, disordered hemostasis, and other factors remain controversial. For more than a century, neuropathologic studies have provided the basis for concepts of causation of cerebral malaria. Magnetic resonance techniques now offer non-invasive means of determining essential anatomic, metabolic, biochemical, and functional features of the brain in patients with cerebral malaria during life that could transform our understanding of the pathogenesis of cerebral malaria and lead to the development of new neuroprotective treatments.

Platelet power: sticky problems for sticky parasites?

Platelets might have a crucial role in the pathogenesis of both human and rodent malarias by assisting in the sequestration of infected erythrocytes within the cerebral vasculature. However, recent elegant work by McMorran et al. suggests that they are also involved in innate protection during the early stages of infection. Here, we discuss the implications of their important findings in the context of immunity to malaria.

Influence of human chorionic gonadotropin (hCG) on in vitro growth of Plasmodium falciparum

BackgroundDuring pregnancy, women are more susceptible to Plasmodium falciparum infections and frequently have a higher parasitaemia than non-pregnant women. Several mechanisms are responsible for their increased susceptibility, including down-modulation of immune responses that aid in parasite clearance and sequestration of infected erythrocytes in the placenta. Early in pregnancy, a third mechanism may contribute to higher parasitaemia, since it has been reported that addition of human chorionic gonadotropin (hCG) to in vitro cultures of the NF54-strain of P. falciparum results in increased parasite growth rates. The goal of this study was to further examine the effect of hCG on P. falciparum growth.MethodsThe NF54-3D7, FVO and 7G8 strains of P. falciparum were cultured in vitro with various physiological concentrations of hCG purchased from three sources. Infected erythrocytes were also co-cultured with a human cell line that naturally secretes hCG.ResultsResults from 14 experiments using different combinations of parasite strains and concentrations of hCG from different sources, as well as the co-culture studies, failed to provide convincing evidence that hCG enhances parasite growth in vitro.ConclusionBased on these data, it seems unlikely that hCG has a direct effect on the rate of parasite growth early in pregnancy.

Perfusion Abnormalities in Children with Cerebral Malaria and Malarial Retinopathy

In patients with cerebral malaria (CM), retinal angiography allows the study of infected central nervous system microvasculature in vivo. We aimed to examine retinal perfusion in children with CM by use of fluorescein angiography to investigate the pathophysiology of CM. We performed fluorescein angiography on children with CM admitted to Queen Elizabeth Central Hospital, Malawi. We related angiograms to funduscopic findings. Fluorescein angiography was performed for 34 patients with CM, and impaired perfusion was identified in 28 (82%). Areas of capillary nonperfusion (CNP) were seen in 26 patients (76%). Multiple, scattered areas of CNP were typical and topographically matched to retinal whitening. Larger retinal vessels were occluded in 9 patients (26%) who had associated ischemia. These vessels appeared white on ophthalmoscopy. Intravascular abnormalities were seen in 9 patients (26%), including filling defects and mottling of the blood column. Limited fluorescein leakage occurred in 15 patients (44%) and was not related to angiographic intravascular abnormalities or visible vessel discoloration. Impaired perfusion occurs in the retinal microvasculature of most children with CM. This is evidence for hypoxia and ischemia as important components in the pathogenesis of CM. Vessel occlusion and filling defects are likely to be due to sequestration of infected erythrocytes. Interventions which improve perfusion or limit hypoxic injury may be beneficial in CM.

In vitro drug sensitivity testing in Plasmodium vivax

The possibility of short-term in vitro cultivation, i.e. growth of asexual erythrocytic stages up to the stage of mature schizonts, permits in principle the development of drug sensitivity tests also for Plasmodium vivax. In the absence of a sequestration of erythrocytes carrying the advanced stages of schizogony, asexual parasites of all stages may be seen in the peripheral blood of patients infected with P. vivax. This precludes schizont maturation tests since schizont development will be unduly influenced by the number of advanced trophozoites. A test system reflecting the age composition of the parasite population and its progression without and under the influence of inhibitors was found to yield precise results also in the higher IC ranges. The population-based test procedure would also permit the identification of any stage-specific impact of antimalarial agents.

Exposure to complement-bearing immune complexes enhances the in vitro sequestration of erythrocytes from young but not elderly donors.

Complement and immunoglobulin have each been claimed to be the major opsonins responsible for sequestration of the effete erythrocyte. Binding of immune complexes to the erythrocyte via CR1 (CD35) provides a model for studying the effects of increments in membrane-bound complement and immunoglobulin on the sequestration of the erythrocyte ('innocent bystander' sequestration). It is possible that C3b-bearing immune complexes (IC-C3b) bound to erythrocyte CR1 contribute to the levels of immunoglobulin and complement fragments detectable on the human erythrocyte. We have, therefore, compared the capacity of erythrocytes from young and elderly donors to bind IC-C3b and the effect of this binding on in vitro sequestration. Erythrocytes from young donors exposed to IC-C3b bind these complexes, as attested by an increment in membrane-bound C3, and undergo 'innocent bystander' sequestration. However, when density-separated erythrocytes are so exposed, it is only the low density (young) erythrocytes from young donors which are susceptible to 'innocent bystander' sequestration. High density (old) erythrocytes from young donors and all erythrocytes from elderly donors show initially high in vitro sequestration and are resistant to the 'innocent bystander' effect. (Those erythrocytes which show initially high in vitro sequestration are referred to collectively as 'in situ aged' erythrocytes.) There is a great similarity between the mechanisms of sequestration of 'in situ aged' and 'innocent bystander' erythrocytes in that they are both inhibited by the integrin binding peptide arginine-glycine-aspartic acid (RGD) and the beta-galactosyl sugar N-acetyl-galactosamine, and unaffected by the Fc-gamma binding protein, Protein-G. Complement is the major opsonin in 'innocent bystander' sequestration since this sequestration occurs whether the isotype of the antibody in the immune complex is IgM or IgG, and Protein-G, which inhibits IgG-dependent erythrophagocytosis, has no effect on 'innocent bystander' sequestration. The present studies demonstrate that in vitro sequestration of 'in situ aged' erythrocytes is similar to complement-dependent 'innocent bystander' sequestration, thus supporting the contention that complement recognition is cardinal in sequestration of 'in situ aged' erythrocytes.

Erythrocytes from young but not elderly donors can bind and degrade immune complex- and antibody-bound C3 in vitro.

In situ aged erythrocytes (senescent erythrocytes from young donors and both young and old erythrocytes from elderly donors) demonstrate high levels of membrane-bound C3c and C3d and elevated susceptibility to in vitro phagocytosis. In this study we demonstrate that in situ aged erythrocytes are defective in their ability to degrade C3 fragments and clear them from the erythrocyte membrane. Erythrocytes from young donors bind complement-bearing immune complexes via CR1 and become susceptible to complement-mediated erythrophagocytosis ('innocent bystander' sequestration). Erythrocytes from elderly donors are defective in their ability to bind such immune complexes, as attested by the lack of an increment in membrane-associated C3 fragments as detected by flow cytometry and lack of an increment in in vitro sequestration. Factor I (serum)-dependent cleavage of C3 fragments and release of immune complexes from the erythrocytes of young donors lead to a drop in erythrocyte-associated C3 fragments and the disappearance of the 'innocent bystander' phenomenon. Inhibition of Factor I, and thus inhibition of C3b degradation and immune complex release for the erythrocyte membrane, enhances the levels of 'innocent bystander' sequestration of erythrocytes from young donors. Erythrocytes from elderly donors are defective in the dynamic process of CR1 binding of complement-bearing immune complexes and Factor I-associated release of membrane-associated C3 fragments. A defect in the ability of all in situ aged erythrocytes to clear their membranes of C3 fragments is also demonstrated for complement bound to the erythrocyte via IgM isoagglutinins. While erythrocytes from both young and elderly donors allow for the IgM-mediated binding of complement to the erythrocyte, only young erythrocytes from young donors demonstrate degradative activity with the release of membrane-associated C3c. Erythrocytes from elderly donors demonstrate lower levels of detectable CR1 (CD35), decay accelerating factor (DAF) (CD55) and Protectin (CD59) than do erythrocytes from young donors. Time course studies determine that the defect in handling of immune complexes observed for in situ aged erythrocytes is not due to differences in the kinetics of loading or releasing of immune complexes. These findings on the refractiveness of erythrocytes of elderly donors to uptake of immune complexes and the degradation of C3 fragments may be of importance not only in the understanding of erythrocyte sequestration, but also in the physiology of immune clearance in the elderly.

Investigation of host factors possibly enhancing the emergence of the chondroitin sulfate A-binding phenotype in Plasmodium falciparum

In malaria endemic areas, regardless of immunity acquired during lifelong exposure to malaria, pregnant women become susceptible to Plasmodium falciparum infections. Malaria during pregnancy is associated with a massive sequestration of infected erythrocytes in the placenta and the emergence of a unique parasite-derived adhesive molecule (encoded by var2CSA) that binds to chondroitin sulfate A (CSA). How P. falciparum achieves the timely expression of the CSA ligand in pregnant women remains puzzling. We investigated whether host serum-specific factors present only during pregnancy may induce var2CSA expression. Our panel of experiments did not reveal significant changes in var2CSA levels and CSA-binding capacity.

`Blood-doping' effects on hematocrit regulation and oxygen consumption in late-stage chicken embryos (Gallus gallus)

The extent to which hematocrit (Hct) is regulated and the impact of altered Hct on blood oxygen transport in avian embryos are largely unknown. Consequently, we investigated how acute blood removal or Ringer solution injection modified Hct in day 15 embryos, and how ;blood doping' with erythrocyte-enriched whole blood influenced O(2) consumption in day 15-17 chicken embryos. Mean Hct (+/-s.e.m.) at day 15, 16 and 17 was 26.7+/-0.6%, 28.0+/-0.4% and 30.7+/-0.5%, respectively. Blood withdrawal (19 increments of 125 microl each, separated by 30 min) caused a progressive fall in Hct to approximately 12% at day 15. Hct decline was strictly proportional to the extent of blood withdrawal. Incremental Ringer solution injection over an 8 h period, transiently increasing blood volume up to 85% over initial values, did not decrease Hct, indicating that injected Ringer solution rapidly left the circulating blood compartment. Blood doping with erythrocyte-enriched whole blood artificially elevated Hct from 27% to 38%, but caused no significant change in routine O(2) consumption (0.35-0.39 ml O(2) min(-1) egg(-1)) at any point over the subsequent 6 h period in day 15-17 embryos. We conclude that Hct is not protected acutely in day 15 chicken embryos, with no evidence of erythrocyte sequestration or release. Additionally, at day 15-17, Hct increases of approximately 10% do not enhance embryonic oxygen consumption, suggesting that blood oxygen carrying capacity per se is not limiting to oxygen consumption.

Stroke in central nervous system infections

Stroke subtypes and etiology may differ between developing and developed countries. Infections are a relatively common cause of stroke in tropical regions. To review the main infectious diseases associated with stroke. Prevalence of stroke in HIV patients is around 1%. Pathogenic mechanisms include HIV vasculopathy, vasculitis, cardioembolism, acquired hypercoagulability, and the effect of opportunistic infections. Treatment with protease inhibitors has been associated with premature atherosclerotic vascular disease. Emerging viral infections that are associated with stroke include viral hemorrhagic fevers, Japanese encephalitis, dengue, and West Nile virus. Vasculitis involving perforating vessels of the brain is a cerebrovascular complication of tuberculous meningitis. Small, medium, and large arteries of the anterior circulation can be involved. A progressive intracranial arteriopathy afterLeptospira interrogansinfection has been described, which involves the large intracranial arteries. Cerebrovascular complications of mycosis are associated with large vessel vasculitis, direct vessel damage by invasion or embolization, and subarachnoid hemorrhage due to mycotic aneurysm rupture. Pathological findings of cerebral malaria include diffuse cerebral edema, perivascular ring hemorrhages, white matter necrosis, parenchyma petechial hemorrhages, occlusion of brain vessels, and sequestration of infected erythrocytes in cortical and perforating arteries. Stroke can occur in subarachnoid neurocysticercosis and the lesions in such cases consist mostly of deep lacunar infarctions resulting from endarteritis of small penetrating arteries. Cardiac arrhythmias, congestive heart failure, apical aneurysm, and mural thrombus are the conditions that predispose patients with American trypanosomiasis to cardioembolism. Gnathostoma spinigerum infestation is a cause of hemorrhagic stroke in Asia. Infectious and tropical diseases should be included in the differential diagnoses of stroke.

Pathogenesis of malaria in pregnancy

Even though we have good tools to prevent and treat malaria, it remains a tragically common disease in poor countries, especially in Africa. Pregnant women are particularly susceptible to malaria, causing anaemia and poor birth outcomes. There is marked sequestration of Plasmodium falciparum-infected erythrocytes (IEs) in the placenta, but the pathogenesis of malaria in pregnancy is still incompletely understood. Both intermittent preventive therapy and insecticide-impregnated bed nets are effective protective measures, but new measures are also needed.

Malaria Treatment in the United States

To the Editor: In their review of the treatment of malaria in the United States, Dr Griffith and colleagues provided a concise summary for clinicians who infrequently encounter malaria. While the information is important, they propose that the second question to be asked when managing malaria is “What is the parasite density?” Although there is an association between the peripheral parasite count and patient outcome, it is a relatively weak one. Other clinical and laboratory variables have stronger prognostic value, particularly acidosis and pulmonary and renal disease. In an international trial, almost 70% of 1050 severe malaria patients had a peripheral parasite count of less than 5%, and the mortality in this population was 18%. Emphasis on a “low” parasite count, rather than disease manifestations, may offer the clinician false reassurance or lead to an underestimation of the contribution of the malaria infection to a patient’s symptoms. The central pathophysiological mechanism in severe malaria is the mechanical microcirculatory obstruction caused by sequestration of infected erythrocytes. This increases as parasites mature during their 48-hour asexual life cycle. Once infected, erythrocytes are adherent to endothelium in the microcirculation; they will no longer appear in the peripheral circulation. Therefore, depending on the stage of the parasites’ life cycle, 2 patients with the same peripheral parasitemia may have as much as a 100fold difference in the total number of parasites in the body. Regarding quinidine, the main parenteral agent discussed in the article, the current World Health Organization treatment guidelines note that quinidine is more toxic than quinine and should only be used if no other effective parenteral drugs are available. The same guidelines recommend artesunate as the treatment of choice in lowtransmission areas, as it has been shown to be associated with a 34.7% relative reduction in mortality compared with quinine; while it is available in many developing countries, it has not yet been approved by the US Food and Drug Administration.

Severe Malaria Increases the List of Heme Oxygenase-1-Protected diseases

Malaria is the most widespread and lethal parasitic disease in the world today, and claims the lives of at least 1 million people every year. The disease is caused by parasitic protozoa of the genus Plasmodium, whose life cycle involves a vertebrate host and a mosquito vector. The parasite undergoes two different stages of infection within the mammalian host. The first stage occurs inside hepatocytes and is clinically asymptomatic. The symptoms associated with the disease appear only during the subsequent stage of infection, which occurs inside erythrocytes. In humans, clinical manifestations of malaria can range from mild to severe malaria, the latter comprising a series of syndromes that include, among others, cerebral malaria (CM) and acute respiratory distress syndrome. Interestingly, although four Plasmodium species infect humans (Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium ovale), only one of these parasites, P. falciparum, causes fatal disease. The reason(s) for this difference are yet to be fully elucidated. The sequestration of infected erythrocytes in vital organs, a feature unique to P. falciparum infection, has been identifed as a major factor. However, whether this feature causes disease due to mechanical blockage of blood flow or to the release of inflammatory mediators in vulnerable regions caused by local infected-erythrocyte rupture, is still a matter of controversy [1], and increasing evidence is suggesting a role for inflammatory mediators in malaria-associated pathology [2]. Thus, it has been proposed that the pathogenesis of malaria might not differ much from other clinically overlapping systemic diseases caused by other pathogens or even nonpathogen-dependent inflammatory syndromes [3]. Recently, we have used mice infected with Plasmodium berghei ANKA, a rodent model of malaria pathology, to demonstrate that the antiinflammatory molecule heme oxygenase (HO)-1, which degrades heme to generate biliverdin, iron and carbon monoxide (CO), prevents the development of experimental CM (ECM) [4]. Moreover, we demonstrated that exposure to the endproduct of HO-1 activity, CO, also protected mice against ECM [4]. The anti-inflammatory effects of HO-1 activation were first reported in experimental sepsis [5], and later extended to inflammation in general [6]. Again, in these cases, CO was shown to be the mediator molecule between HO-1 activity and protection against inflammation [6]. More recently, it was postulated that the inhibitory effects of CO observed in systemic inflammation, and the role of TNF-induced HO-1, might also play a role in a malarial context [3]. In fact, HO-1 was detected in histological sections from human sepsis and malaria cases [7].