Role In Pathogenesis Of Malaria Research Articles

DNA-Containing Immunocomplexes Promote Inflammasome Assembly and Release of Pyrogenic Cytokines by CD14+ CD16+ CD64high CD32low Inflammatory Monocytes from Malaria Patients.

ABSTRACTHigh levels of circulating immunocomplexes (ICs) are found in patients with either infectious or sterile inflammation. We report that patients with either Plasmodium falciparum or Plasmodium vivax malaria have increased levels of circulating anti-DNA antibodies and ICs containing parasite DNA. Upon stimulation with malaria-induced ICs, monocytes express an NF-κB transcriptional signature. The main source of IC-induced proinflammatory cytokines (i.e., tumor necrosis factor alpha [TNF-α] and interleukin-1β [IL-1β])in peripheral blood mononuclear cells from acute malaria patients was found to be a CD14+ CD16 (FcγRIIIA)+ CD64 (FcγRI)high CD32 (FcγRIIB)low monocyte subset. Monocytes from convalescent patients were predominantly of the classical phenotype (CD14+ CD16−) that produces high levels of IL-10 and lower levels of TNF-α and IL-1β in response to ICs. Finally, we report a novel role for the proinflammatory activity of ICs by demonstrating their ability to induce inflammasome assembly and caspase-1 activation in human monocytes. These findings illuminate our understanding of the pathogenic role of ICs and monocyte subsets and may be relevant for future development of immunity-based interventions with broad applications to systemic inflammatory diseases.

The Role of Platelets in Malarial Acute Lung Injury and Acute Respiratory Distress Syndrome: A World of Possibilities

In recent decades our understanding of platelets' role in immune response has increased. Traditionally platelets were considered as bleeding-stopping and thrombosis-causing cells. In recent years the platelets' role in malarial innate and adaptive immune responses is being recognized. Platelets play critical role in pathogenesis of malaria infection leading to variety of outcomes. It is being realized that platelets play dual role in case of malaria (i) by preventing early stage exponential growth of parasitemia (ii) promoting exaggerated immune responses later. Platelets role in pathogenesis of severe and cerebral malaria has been widely studied. However their role in malaria related acute lung injury and respiratory distress has gained less attention. Recently the presence of active megakaryocytes and proplatelets have been explained in human lungs. Simultaneously, the platelets role in pathogenesis of acute lung injury and respiratory distress (ALI/ARDS) was also recognized. This gives a hint that there is a possible association of platelets with malaria related respiratory diseases as well. ALI/ARDS are characterized by lung edema due to increased permeability of the alveolar-capillary barrier and subsequent impairment of arterial oxygenation. In this review we have attempted to establish the importance of role of platelets in malaria related acute lungs injury and malaria acute respiratory distress syndrome and try to explain the underlying mechanism of this process. In ALI/ARDS, including those caused by malaria, platelets participate sequestration to the vascular bundle facilitating the recruitment of immune cells viz. neutrophils. Additionally, they secrete or induce the secretion of chemokines that result into vascular damage.

Interactions between Plasmodium falciparum skeleton-binding protein 1 and the membrane skeleton of malaria-infected red blood cells

During development inside red blood cells (RBCs), Plasmodium falciparum malaria parasites export proteins that associate with the RBC membrane skeleton. These interactions cause profound changes to the biophysical properties of RBCs that underpin the often severe and fatal clinical manifestations of falciparum malaria. P. falciparum erythrocyte membrane protein 1 (PfEMP1) is one such exported parasite protein that plays a major role in malaria pathogenesis since its exposure on the parasitised RBC surface mediates their adhesion to vascular endothelium and placental syncytioblasts. En route to the RBC membrane skeleton, PfEMP1 transiently associates with Maurer's clefts (MCs), parasite-derived membranous structures in the RBC cytoplasm. We have previously shown that a resident MC protein, skeleton-binding protein 1 (SBP1), is essential for the placement of PfEMP1 onto the RBC surface and hypothesised that the function of SBP1 may be to target MCs to the RBC membrane. Since this would require additional protein interactions, we set out to identify binding partners for SBP1. Using a combination of approaches, we have defined the region of SBP1 that binds specifically to defined sub-domains of two major components of the RBC membrane skeleton, protein 4.1R and spectrin. We show that these interactions serve as one mechanism to anchor MCs to the RBC membrane skeleton, however, while they appear to be necessary, they are not sufficient for the translocation of PfEMP1 onto the RBC surface. The N-terminal domain of SBP1 that resides within the lumen of MCs clearly plays an essential, but presently unknown role in this process.

In Vitro Activity of Cocoa Powder Extracts on Some Biomarkers Implicated in P. falciparum Malaria Pathogenesis

Malaria is a public health concern in many developing countries, including Ghana, and efforts are being made to eradicate it. Extracts from natural products have been used in several malaria endemic areas for malaria prophylaxis and treatment. Natural cocoa powder has been reported to possess in vitro direct inhibitory on P. falciparum. This study investigated the effect of natural cocoa powder on inducible nitric oxide, TNF-α and IL-10, biomarkers that play different roles in malaria pathogenesis. Chloroform and ethylacetate fractions of cocoa powder were cultured together with phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMCs) for 24 hours at 37°C with 5% CO2. Cell free supernatants were harvested and assayed for iNO, TNF-α and IL-10. Inducible NO was determined by diazotization reaction developed by Griess. TNF-α and IL-10 were determined by ELISA. This study showed that TNF-α and iNO in phytohemagglutinin-stimulated PBMCs were significantly reduced by cocoa fractions (p < 0.05), but IL-10 levels did not change significantly (p > 0.05), although TNF-α is known to up-regulate IL-10.Apart from the documented direct inhibitory effect of cocoa powder on P. falciparum, it can be hypothesized that the antiplasmodial activity of unsweetened cocoa powder could also be due to its ability to significantly inhibit iNO and TNF-α, inflammatory substances implicated in severe malaria pathogenesis.

Maturation of Plasmodium falciparum in multiply infected erythrocytes and the potential role in malaria pathogenesis.

Erythrocytes containing two or more parasites, referred to here as multiply infected erythrocytes (MIEs), are common in the blood of humans infected by Plasmodium falciparum. It is necessary to study these cells closely because the excess numbers of parasites they contain suggest that they could be overloaded with virulence factors. Here, microscopic examinations of blood smears from patients showed that up to seven merozoites can successfully invade an erythrocyte and mature to ring stage. However, in vitro culture showed that only up to three parasites can mature to late schizont stage. These observations were made by culturing the parasites in erythrocytes containing hemoglobin AA (HbAA), HbAS, and HbSS. Biochemical analysis of saponin-concentrated culture suggests that more hemozoin is produced in a MIE than in a singly infected erythrocyte (SIE). Studies have shown that ingestion of excessive hemozoin destroys monocytes and neutrophils, which could impair the immune system. Cultured parasites were also examined by transmission electron microscopy, and it was found that the quantity of knobs was dramatically increased on the membranes of erythrocytes containing multiple schizonts, compared to those containing only one schizont. Knobs contain, among other things, P. falciparum erythrocyte membrane protein 1 (PfEMP1) complex which mediates sequestration and promotes severe malaria. These findings suggest that P. falciparum increases its virulence by producing MIEs. On sexual life cycle of the parasite, microphotographs are presented in this report showing, for the first time, that two gametocytes can develop in one erythrocyte; they are referred to here as twin gametocytes. It is not known whether they can infect mosquitoes.

An exported kinase (FIKK4.2) that mediates virulence-associated changes in Plasmodium falciparum-infected red blood cells

Alteration of the adhesive and mechanical properties of red blood cells caused by infection with the malaria parasite Plasmodium falciparum underpin both its survival and extreme pathogenicity. A unique family of parasite putative exported kinases, collectively called FIKK (Phenylalanine (F) – Isoleucine (I) – Lysine (K) – Lysine (K)), has recently been implicated in these pathophysiological processes, however, their precise function in P. falciparum-infected red blood cells or their likely role in malaria pathogenesis remain unknown. Here, for the first time, we demonstrate that one member of the FIKK family, FIKK4.2, can function as an active kinase and is localised in a novel and distinct compartment of the parasite-infected red blood cell which we have called K-dots. Notably, targeted disruption of the gene encoding FIKK4.2 (fikk4.2) dramatically alters the parasite’s ability to modify and remodel the red blood cells in which it multiplies. Specifically, red blood cells infected with fikk4.2 knockout parasites were significantly less rigid and less adhesive when compared with red blood cells infected with normal parasites from which the transgenic clones had been derived, despite expressing similar levels of the major cytoadhesion ligand, PfEMP1, on the red blood cell surface. Notably, these changes were accompanied by dramatically altered knob-structures on infected red blood cells that play a key role in cytoadhesion which is responsible for much of the pathogenesis associated with falciparum malaria. Taken together, our data identifies FIKK4.2 as an important kinase in the pathogenesis of P. falciparum malaria and strengthens the attractiveness of FIKK kinases as targets for the development of novel next-generation anti-malaria drugs.

Induction of Strain-Transcending Antibodies Against Group A PfEMP1 Surface Antigens from Virulent Malaria Parasites

Sequence diversity in pathogen antigens is an obstacle to the development of interventions against many infectious diseases. In malaria caused by Plasmodium falciparum, the PfEMP1 family of variant surface antigens encoded by var genes are adhesion molecules that play a pivotal role in malaria pathogenesis and clinical disease. PfEMP1 is a major target of protective immunity, however, development of drugs or vaccines based on PfEMP1 is problematic due to extensive sequence diversity within the PfEMP1 family. Here we identified the PfEMP1 variants transcribed by P. falciparum strains selected for a virulence-associated adhesion phenotype (IgM-positive rosetting). The parasites transcribed a subset of Group A PfEMP1 variants characterised by an unusual PfEMP1 architecture and a distinct N-terminal domain (either DBLα1.5 or DBLα1.8 type). Antibodies raised in rabbits against the N-terminal domains showed functional activity (surface reactivity with live infected erythrocytes (IEs), rosette inhibition and induction of phagocytosis of IEs) down to low concentrations (<10 µg/ml of total IgG) against homologous parasites. Furthermore, the antibodies showed broad cross-reactivity against heterologous parasite strains with the same rosetting phenotype, including clinical isolates from four sub-Saharan African countries that showed surface reactivity with either DBLα1.5 antibodies (variant HB3var6) or DBLα1.8 antibodies (variant TM284var1). These data show that parasites with a virulence-associated adhesion phenotype share IE surface epitopes that can be targeted by strain-transcending antibodies to PfEMP1. The existence of shared surface epitopes amongst functionally similar disease-associated P. falciparum parasite isolates suggests that development of therapeutic interventions to prevent severe malaria is a realistic goal.

Cerebral malaria: human versus mouse studies

In a recent Opinion article [1], White and colleagues discuss the value of the murine Plasmodium berghei ANKA model in identifying pathological processes and therapeutic interventions in human cerebral malaria (HCM). This model involves P. berghei ANKA infection of inbred CBA or C57BL/6 strain mice, which develop clinical symptoms of cerebral complications including paralysis, fitting and coma with death around Day 8 post-infection [2]. Resistant mouse strains such as BALB/c mice develop hyperparasitemia and severe anemia with death occurring about 3 weeks after infection.

ADAMTS13 Deficiency with Elevated Levels of Ultra-Large and Active von Willebrand Factor in P. falciparum and P. vivax Malaria

A deficiency in ADAMTS13 (a von Willebrand factor [VWF] cleaving protease) is associated with accumulation of prothrombogenic unusually large VWF multimers (UL-VWF) in plasma. We studied VWF release and proteolysis in patients with symptomatic Plasmodium falciparum or P. vivax malaria on the Indonesian island Sumba. Malaria patients had significantly lower platelet counts and higher VWF concentrations and VWF activation factors than healthy hospital staff controls. The latter indicates that a higher amount of circulating VWF was in a conformation enabling spontaneous platelet binding. In addition, ADAMTS13 activity and antigen levels were reduced in both malaria groups, and this was associated with the appearance of UL-VWF. The mechanism behind this reduction and the role in malaria pathogenesis needs to be further elucidated. In malaria, endothelial cell activation with increased circulating amounts of active and ultra-large VWF, together with reduced VWF inactivation by ADAMTS13, may result in intravascular platelet aggregation, thrombocytopenia, and microvascular disease.

Putative DNA G-quadruplex formation within the promoters of Plasmodium falciparum var genes

BackgroundGuanine-rich nucleic acid sequences are capable of folding into an intramolecular four-stranded structure called a G-quadruplex. When found in gene promoter regions, G-quadruplexes can downregulate gene expression, possibly by blocking the transcriptional machinery. Here we have used a genome-wide bioinformatic approach to identify Putative G-Quadruplex Sequences (PQS) in the Plasmodium falciparum genome, along with biophysical techniques to examine the physiological stability of P. falciparum PQS in vitro.ResultsWe identified 63 PQS in the non-telomeric regions of the P. falciparum clone 3D7. Interestingly, 16 of these PQS occurred in the upstream region of a subset of the P. falciparum var genes (group B var genes). The var gene family encodes PfEMP1, the parasite's major variant antigen and adhesin expressed at the surface of infected erythrocytes, that plays a key role in malaria pathogenesis and immune evasion. The ability of the PQS found in the upstream regions of group B var genes (UpsB-Q) to form stable G-quadruplex structures in vitro was confirmed using 1H NMR, circular dichroism, UV spectroscopy, and thermal denaturation experiments. Moreover, the synthetic compound BOQ1 that shows a higher affinity for DNA forming quadruplex rather than duplex structures was found to bind with high affinity to the UpsB-Q.ConclusionThis is the first demonstration of non-telomeric PQS in the genome of P. falciparum that form stable G-quadruplexes under physiological conditions in vitro. These results allow the generation of a novel hypothesis that the G-quadruplex sequences in the upstream regions of var genes have the potential to play a role in the transcriptional control of this major virulence-associated multi-gene family.

Does activation of the blood coagulation cascade have a role in malaria pathogenesis?

Plasmodium falciparum infection is often associated with a procoagulant state. Recent identification of tissue factor in the brain endothelium of patients who have died from cerebral malaria casts new light on our understanding of the coagulation disorder found in P. falciparum infection. It has also been revealed that parasitized red blood cells support the assembly of multimolecular coagulation complexes. Tissue factor expression by the endothelium and amplification of the coagulation cascade by parasitized red blood cells and/or activated platelets (particularly at sequestration sites) have crucial roles in mounting and sustaining a coagulation-inflammation cycle which contributes to organ dysfunction and coma in falciparum malaria.

Rosetting in Plasmodium falciparum: A cytoadherence phenotype with multiple actors

The capacity of Plasmodium falciparum-infected red blood cells to bind uninfected red blood cells (“rosetting”) has been associated with high parasite density in numerous geographic areas and with severe malaria in African children. We summarize here the associations that have emerged from field studies and describe the various experimental models of rosetting that have been developed. A variety of erythrocyte receptors, several serum factors and a number of rosette-mediating PfEMP1 adhesins have been identified. Several var genes code for rosette-forming PfEMP1 adhesins in each P. falciparum genome, so that each clonal line has the capacity to generate distinct types of rosettes. To clarify their respective role in malaria pathogenesis, each of the multiple ligand/receptor interactions should be further studied for fine specificity, binding affinity and the impact of the large population polymorphism of the parasite variant repertoires should be assessed. Interestingly, some major human erythrocyte surface polymorphisms have been identified as affecting rosette formation, consistent with a role for rosetting in life-threatening falciparum malaria.

Plasmodium falciparum Uses gC1qR/HABP1/p32 as a Receptor to Bind to Vascular Endothelium and for Platelet-Mediated Clumping

The ability of Plasmodium falciparum–infected red blood cells (IRBCs) to bind to vascular endothelium, thus enabling sequestration in vital host organs, is an important pathogenic mechanism in malaria. Adhesion of P. falciparum IRBCs to platelets, which results in the formation of IRBC clumps, is another cytoadherence phenomenon that is associated with severe disease. Here, we have used in vitro cytoadherence assays to demonstrate, to our knowledge for the first time, that P. falciparum IRBCs use the 32-kDa human protein gC1qR/HABP1/p32 as a receptor to bind to human brain microvascular endothelial cells. In addition, we show that P. falciparum IRBCs can also bind to gC1qR/HABP1/p32 on platelets to form clumps. Our study has thus identified a novel host receptor that is used for both adhesion to vascular endothelium and platelet-mediated clumping. Given the association of adhesion to vascular endothelium and platelet-mediated clumping with severe disease, adhesion to gC1qR/HABP1/p32 by P. falciparum IRBCs may play an important role in malaria pathogenesis.

Changes in var gene mRNA levels during erythrocytic development in two phenotypically distinct Plasmodium falciparum parasites

BackgroundThe var multigene family encodes PfEMP1, which are expressed on the surface of infected erythrocytes and bind to various host endothelial receptors. Antigenic variation of PfEMP1 plays a key role in malaria pathogenesis, a process partially controlled at the level of var gene transcription. Transcriptional levels, throughout the intra-erythrocytic cycle, of 59 var genes of the NF54 clone were measured simultaneously by quantitative real-time PCR. The timing of var transcript abundance, the number of genes transcribed and whether transcripts were correctly spliced for protein expression were determined. Two parasite populations were studied; an unselected population of NF54 and a selected population, NF54VAR2CSA, to compare both the transcription of var2csa and the expression pattern of the corresponding protein.MethodsSynchronized parasites were harvested at different time points along the 48 hours intra-erythrocytic cycle for extraction of RNA and for analysis of expression of variant surface antigens by flow cytometry. Total RNA from each parasite sample was extracted and cDNA synthesized. Quantitative real-time PCR was performed using gene-specific primers for all var genes. Samples for flow cytometry were labelled with rabbit IgG targeting DBL5ε of VAR2CSA and serum IgG from malaria-exposed men and pregnant women.Resultsvar transcripts were detected at all time points of the intra-erythrocytic cycle by quantitative real-time PCR, although transcription peaked in ring-stage parasites. There was no difference in the timing of appearance of group A, B or C transcripts, and dominant and subdominant var transcripts appeared to be correctly spliced at all time points. VAR2CSA appeared on the surface of infected erythrocytes 16 hours after invasion, consistent with previous studies of other PfEMP1. Transcription of the pseudogene var1csa could not be detected in NF54VAR2CSA cells.ConclusionThe optimal sampling point for analysis of var transcripts using quantitative real-time PCR is the ring-stage, which is encouraging for the analysis of fresh clinical isolates. The data presented here indicate that there is no promiscuous transcription of var genes at the individual cell level and that it is possible to correlate dominant transcripts with adhesion phenotype and clinical markers of malaria severity.

Patterns of gene recombination shape var gene repertoires in Plasmodium falciparum: comparisons of geographically diverse isolates

BackgroundVar genes encode a family of virulence factors known as PfEMP1 (Plasmodium falciparum erythrocyte membrane protein 1) which are responsible for both antigenic variation and cytoadherence of infected erythrocytes. Although these molecules play a central role in malaria pathogenesis, the mechanisms generating variant antigen diversification are poorly understood. To investigate var gene evolution, we compared the variant antigen repertoires from three geographically diverse parasite isolates: the 3D7 genome reference isolate; the recently sequenced HB3 isolate; and the IT4/25/5 (IT4) parasite isolate which retains the capacity to cytoadhere in vitro and in vivo.ResultsThese comparisons revealed that only two var genes (var1csa and var2csa) are conserved in all three isolates and one var gene (Type 3 var) has homologs in IT4 and 3D7. While the remaining 50 plus genes in each isolate are highly divergent most can be classified into the three previously defined major groups (A, B, and C) on the basis of 5' flanking sequence and chromosome location. Repertoire-wide sequence comparisons suggest that the conserved homologs are evolving separately from other var genes and that genes in group A have diverged from other groups.ConclusionThese findings support the existence of a var gene recombination hierarchy that restricts recombination possibilities and has a central role in the functional and immunological adaptation of var genes.

Differential var gene transcription in Plasmodium falciparum isolates from patients with cerebral malaria compared to hyperparasitaemia

The Plasmodium falciparum variant erythrocyte surface antigens known as PfEMP1, encoded by the var gene family, are thought to play a crucial role in malaria pathogenesis because they mediate adhesion to host cells and immuno-modulation. Var genes have been divided into three major groups (A, B and C) and two intermediate groups (B/A and B/C) on the basis of their genomic location and upstream sequence. We analysed expressed sequence tags of the var gene DBLα domain to investigate var gene transcription in relation to disease severity in Malian children. We found that P. falciparum isolates from children with cerebral malaria (unrousable coma) predominantly transcribe var genes with DBLα1-like domains that are characteristic of Group A or B/A var genes. In contrast, isolates from children with equally high parasite burdens but no symptoms or signs of severe malaria (hyperparasitaemia patients) predominantly transcribe var genes with DBLα0-like domains that are characteristic of the B and C-related var gene groups. These results suggest that var genes with DBLα1-like domains (Group A or B/A) may be implicated in the pathogenesis of cerebral malaria, while var genes with DBLα0-like domains promote less virulent malaria infections.

Modulation of malaria virulence by determinants of Plasmodium falciparum erythrocyte membrane protein-1 display

Plasmodium falciparum malaria parasites carry approximately 60 var genes that encode variable adhesins termed P. falciparum erythrocyte membrane protein-1. Clonal expression of a single P. falciparum erythrocyte membrane protein-1 variant on the surface of the parasitized host erythrocyte promotes binding of the cell to blood elements (including noninfected erythrocytes, leukocytes) and walls of microvessels. These binding events enable parasitized erythrocytes to sequester and avoid clearance by the spleen, and they also contribute to disease by causing microvascular inflammation and obstruction. Steps by which P. falciparum erythrocyte membrane protein-1 is exported to the parasitized erythrocyte surface have recently been elucidated. The ability of parasites to cytoadhere and cause disease depends on the variant of P. falciparum erythrocyte membrane protein-1 as well as its amount and distribution at the erythrocyte surface. An example of a host polymorphism that affects P. falciparum erythrocyte membrane protein-1 display is hemoglobin C, which may protect against malaria by impairing the parasite's ability to adhere to microvessels and induce inflammation. Interference with P. falciparum erythrocyte membrane protein-1-mediated phenomena appears to diminish cytoadherence in vivo and to protect against disease in animal models. Plasmodium falciparum erythrocyte membrane protein-1-mediated sequestration of parasitized erythrocytes plays a central role in malaria pathogenesis. Clinical interventions aimed at reducing cytoadherence and microvascular inflammation may improve disease outcome.

Antibodies from malaria-exposed pregnant women recognize trypsin resistant epitopes on the surface of Plasmodium falciparum-infected erythrocytes selected for adhesion to chondroitin sulphate A

BackgroundThe ability of Plasmodium falciparum-infected erythrocytes to adhere to the microvasculature endothelium is thought to play a causal role in malaria pathogenesis. Cytoadhesion to endothelial receptors is generally found to be highly sensitive to trypsinization of the infected erythrocyte surface. However, several studies have found that parasite adhesion to placental receptors can be markedly less sensitive to trypsin. This study investigates whether chondroitin sulphate A (CSA) binding parasites express trypsin-resistant variant surface antigens (VSA) that bind female-specific antibodies induced as a result of pregnancy associated malaria (PAM).MethodsFluorescence activated cell sorting (FACS) was used to measure the levels of adult Scottish and Ghanaian male, and Ghanaian pregnant female plasma immunoglobulin G (IgG) that bind to the surface of infected erythrocytes. P. falciparum clone FCR3 cultures were used to assay surface IgG binding before and after selection of the parasite for adhesion to CSA. The effect of proteolytic digestion of parasite erythrocyte surface antigens on surface IgG binding and adhesion to CSA and hyaluronic acid (HA) was also studied.ResultsP. falciparum infected erythrocytes selected for adhesion to CSA were found to express trypsin-resistant VSA that are the target of naturally acquired antibodies from pregnant women living in a malaria endemic region of Ghana. However in vitro adhesion to CSA and HA was relatively trypsin sensitive. An improved labelling technique for the detection of VSA expressed by CSA binding isolates has also been described.ConclusionThe VSA expressed by CSA binding P. falciparum isolates are currently considered potential targets for a vaccine against PAM. This study identifies discordance between the trypsin sensitivity of CSA binding and surface recognition of CSA selected parasites by serum IgG from malaria exposed pregnant women. Thus, the complete molecular definition of an antigenic P. falciparum erythrocyte surface protein that can be used as a malaria in pregnancy vaccine has not yet been achieved.

Modulation of immune response in Plasmodium falciparum malaria: role of IL-12, IL-18 and TGF-beta.

The interaction between pro- and anti-inflammatory cytokines such as interleukin 12 (IL-12), interleukin 18 (IL-18) and transforming growth factor beta (TGF-beta) plays an important role in malaria pathogenesis and outcome, modulating the immunoresponse in Plasmodium falciparum malaria. In our previous studies, we analyzed the plasmatic levels of IL-12, IL-18 and TGF-beta in 105 African children with different degrees of malaria and we correlated the production of these cytokines with the severity of the disease. The aim of the present study was to analyze with a mathematical model, taking into account all the relationships between these cytokines and the parameter variations involved in malaria pathogenesis that influence the results of each type of treatment or therapeutic protocol on patients at different stages of the disease. A mathematical correlation was demonstrated between the levels of pro-inflammatory and anti-inflammatory cytokines, and from this it was possible to build curves of reference in which each patient was positioned based on IL-12 level. Our data, obtained in patients with mild and severe diseases, demonstrate that the levels of IL-12 represent a reliable parameter to predict the progression of the disease, which may be complemented or modulated by administration of IL-18 and TGF-beta. Our findings provide future implications for an immune therapy against the P. falciparum malaria infection, especially in the early phase of the disease showing that a more aggressive outcome may be due to the lack of a balanced immune response.

Identification of a conserved Plasmodium falciparum var gene implicated in malaria in pregnancy.

The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family is a highly polymorphic class of variant surface antigens encoded by var genes that play an important role in malaria pathogenesis. This report describes the unexpected finding that 1 of the var genes encoding a PfEMP1 variant that binds to the host receptor chondroitin sulfate A (CSA) and is implicated in malaria in pregnancy is well conserved among P. falciparum isolates worldwide. The N-terminal domains of this PfEMP1 variant are especially highly conserved, whereas the functional CSA binding domain is more variable. Analysis of var gene expression in placental parasites from primigravid women in Malawi did not support a role for this conserved gene in placental infection but identified a second commonly occurring var gene. These results indicate the need for reevaluation of previous assumptions of a minimal overlap between var gene repertoires from different parasite isolates.