Parasitized Erythrocytes Research Articles

Development and validation of a multiplex, real-time PCR assay for Babesia rossi and Babesia vogeli

Canine babesiosis is caused by tick-transmitted intraerythrocytic protozoan parasites occurring worldwide. In southern Africa, babesiosis is caused by Babesia rossi and B. vogeli and is one of the most common and important infectious diseases affecting dogs. There is no reliable, rapid and sensitive method for the detection of these parasites, especially when parasitaemia is low. The aim of this study was to develop a sensitive and specific multiplex TaqMan® MGB PCR assay for the diagnosis of canine babesiosis infections occurring in southern Africa, and to discriminate between Babesia rossi and B. vogeli. The fitness of purpose of the assay was to confirm diagnosis of suspect or clinical cases, and estimate prevalence of infection for research purposes.A total of 648 published sequences were used to design the assay. A set of group-specific canine Babesia spp. primers were designed to amplify a 117 nucleotide region of the 18S rRNA gene of all canine Babesia spp. Species-specific TaqMan® MGB probes were developed for B. rossi, B. vogeli, B. canis and B. gibsoni, but analytical validation was only performed for B. rossi and B. vogeli as a multiplex assay.The assay had a broad dynamic range and amplified B. rossi and B. vogeli efficiently (98.6% and 94.7% respectively). The assay was sensitive, with a 95% LOD of 10−2.67% parasitized erythrocytes (PE) for B. rossi and 10-2.03% PE for B. vogeli, and specific, with no cross reaction between B. rossi and B. vogeli and no detection of other haemoparasites that infect dogs, such as Ehrlichia canis and Anaplasma platys. Consistent repeatability within and between PCR runs was shown.This assay will be able to accurately and rapidly confirm babesiosis in canines and allow for treatment to be administered in the early stages of the disease, speeding up the recovery time in affected dogs.

Multiplex hydrolysis-probe assay for the simultaneous detection of Theileria equi and Babesia caballi infections in equids

Quantitative real-time PCR assays previously developed for the detection of Theileria equi and Babesia caballi, were combined in a single multiplex TaqMan qPCR platform for the simultaneous detection of both heamoprotozoan parasites in equids. The multiplex equine piroplasmosis (M-EP) qPCR assay was shown to be efficient and specific. The detection limit was determined to be 1.4 × 10−4 % parasitized erythrocytes (PE) for T. equi and 2.8 × 10−4 % PE for B. caballi. The effect of differential DNA concentrations on the outcome of the M-EP qPCR for each target species was also investigated. The data demonstrated that the assay could reliably detect both targets, over a range of at least 1000-fold difference in target concentrations, without loss of sensitivity. The assay was subsequently evaluated on 243 field samples collected from areas where limited tick control strategies were implemented. The IFAT detected circulating T. equi and B. caballi antibodies in 100% and 92% of the samples, respectively. The M-EP qPCR assay detected T. equi parasite DNA in 98% of the samples, while B. caballi could only be detected in 6% of the samples tested, confirming that B. caballi infections generally occur at extremely low parasitaemias that rarely exceed 1%. The developed M-EP qPCR assay therefore serves as a reliable tool for the rapid diagnosis and epidemiological survey of equine piroplasmosis.

Infectivity of Plasmodium falciparum in Malaria-Naive Individuals Is Related to Knob Expression and Cytoadherence of the Parasite.

Plasmodium falciparum is the most virulent human malaria parasite because of its ability to cytoadhere in the microvasculature. Nonhuman primate studies demonstrated relationships among knob expression, cytoadherence, and infectivity. This has not been examined in humans. Cultured clinical-grade P. falciparum parasites (NF54, 7G8, and 3D7B) and ex vivo-derived cell banks were characterized. Knob and knob-associated histidine-rich protein expression, CD36 adhesion, and antibody recognition of parasitized erythrocytes (PEs) were evaluated. Parasites from the cell banks were administered to malaria-naive human volunteers to explore infectivity. For the NF54 and 3D7B cell banks, blood was collected from the study participants for in vitro characterization. All parasites were infective in vivo However, infectivity of NF54 was dramatically reduced. In vitro characterization revealed that unlike other cell bank parasites, NF54 PEs lacked knobs and did not cytoadhere. Recognition of NF54 PEs by immune sera was observed, suggesting P. falciparum erythrocyte membrane protein 1 expression. Subsequent recovery of knob expression and CD36-mediated adhesion were observed in PEs derived from participants infected with NF54. Knobless cell bank parasites have a dramatic reduction in infectivity and the ability to adhere to CD36. Subsequent infection of malaria-naive volunteers restored knob expression and CD36-mediated cytoadherence, thereby showing that the human environment can modulate virulence.

P8 Endothelial dysfunction in systemic lupus erythematosus

Sequestration of parasitized erythrocytes (PE) in the microvasculature contributes directly to the virulence and severe pathology of Plasmodium falciparum malaria. The scavenger receptor CD36 appears to play an important role in PE adherence. Recently several mutations in the CD36 gene have been found to be associated with variability in susceptibility to P. falciparum infection in different ethnic populations. We investigated the possible association of T188G CD36 gene polymorphism with severe clinical manifestations of malaria in 95 adult patients with severe malaria admitted to SCB Medical College Hospital, Cuttack, Orissa, India (‘severe’ group) and 95 ethnically matched controls attending outpatient clinics at primary health centres (‘mild’ group). The frequency of the wild-type (T188T) allele of the CD36 gene was 0.91 in the ‘severe’ group and 0.78 in the ‘mild’ group of patients, while mutant (T188G) allele frequency was 0.09 in the severe group and 0.22 in the mild group. The Hardy-Weinberg equation indicates that the mutant allele is under selection pressure and disease association analysis shows that the presence of the heterozygote mutant allele renders protection against severe malaria (χ2 = 10.67, odds ratio = 3.51, 95% CI 1.67–7.36).

Sequence heterogeneity in the equi merozoite antigen gene ( ema-1) of Theileria equi and development of an ema-1-specific TaqMan MGB™ assay for the detection of T. equi

Although a quantitative real-time PCR assay (qPCR) assay for the detection of Theileria equi has been developed and evaluated, it is possible that additional, as yet undetected 18S rRNA gene sequence variants may exist. A qPCR assay targeting a different gene, used in conjunction with the T. equi 18S rRNA qPCR assay, could assist in the detection of all T. equi genotypes in field samples. A T. equi ema-1-specific qPCR ( Ueti et al., 2003) was tested on 107 South African field samples, 90 of which tested positive for T. equi antibody using the immuno-fluorescent antibody test (IFAT). The qPCR assay performed poorly, as T. equi was detected in only 67 of the 90 IFAT-positive field samples at quantification cycle ( C q) values ranging from 27 to 39.95. Furthermore, a high C q value of 36.18 was obtained from DNA extracted from a South African in vitro-cultured T. equi WL isolate [1.38% parasitized erythrocytes (PE)] when a low C q value (indicative of a high T. equi DNA concentration) was expected. Approximately 600 bp of the ema-1 gene from 38 South African samples were sequenced and BLASTN analysis confirmed all sequences to be merozoite surface protein genes, with an identity of 87.1–100% to previously published T. equi ema-1 gene sequences. Alignment of the sequences revealed extensive sequence variations in the target regions of the primers and probes ( Ueti et al., 2003), explaining the poor performance of the qPCR assay. Based on these observations, we developed a new TaqMan minor-groove binder (MGB™) probe-based qPCR assay, targeting a more conserved region of the ema-1 gene. This assay was shown to be efficient and specific, and the detection limit, defined as the concentration at which 95% of T. equi-positive samples are detected, was determined to be 1.4 × 10 −4% PE. The two ema-1 assays were compared by testing 41 South African field samples in parallel. The results suggested that the new assay was more sensitive than the original assay, as T. equi was detected in more samples and at lower C q values when the new assay was used. Phylogenetic analyses of the 18S rRNA gene sequences and ema-1 amino acid sequences from the same samples showed inconsistencies between the clades, indicating that the T. equi 18S rRNA genetic groups previously identified in South Africa may not represent distinct T. equi lineages. It is possible that the different T. equi ema-1 genotypes could be related to antigenic variability and pathogenicity and may be associated with clinical differences in equine piroplasmosis cases, but this remains to be elucidated.

Development and evaluation of real-time PCR assays for the quantitative detection of Babesia caballi and Theileria equi infections in horses from South Africa

A quantitative real-time polymerase chain reaction (qPCR) assay using a TaqMan minor groove binder (MGB™) probe was developed for the detection of Babesia caballi infection in equids from South Africa. Nine previously published sequences of the V4 hypervariable region of the B. caballi 18S rRNA gene were used to design primers and probes to target unique, conserved regions. The B. caballi TaqMan MGB™ qPCR assay was shown to be efficient and specific. The detection limit, defined as the concentration at which 95% of positive samples can be detected, was determined to be 0.000114% parasitized erythrocytes (PE). We further evaluated a previously reported Theileria equi-specific qPCR assay and showed that it was able to detect the 12 T. equi 18S rRNA sequence variants previously identified in South Africa. Both qPCR assays were tested on samples from two ponies experimentally infected with either T. equi or B. caballi. The qPCR assays were more sensitive than the indirect fluorescent antibody test (IFAT) and the reverse-line blot (RLB) during the early onset of the disease. The assays were subsequently tested on field samples collected from 41 horses, resident on three stud farms in the Northern Cape Province, South Africa. The IFAT detected circulating T. equi and B. caballi antibody in, respectively, 83% and 70% of the samples. The RLB detected T. equi parasite DNA in 73% of the samples, but none of the samples were positive for B. caballi, although 19 T. equi-positive samples also hybridized to the Babesia genus-specific probe. This could indicate a mixed T. equi and B. caballi infection in these samples, with either the B. caballi parasitaemia at a level below the detection limit of the B. caballi RLB probe, or the occurrence of a novel Babesia genotype or species. In contrast, the qPCR assays correlated fairly well with the IFAT. The B. caballi TaqMan MGB™ qPCR assay was able to detect B. caballi parasite DNA in 78% of the samples. The T. equi-specific qPCR assay could positively detect T. equi DNA in 80% of the samples. These results suggest that the qPCR assays are more sensitive than the RLB assay for the detection of T. equi and B. caballi infections in field samples.

C5a Enhances Dysregulated Inflammatory and Angiogenic Responses to Malaria In Vitro: Potential Implications for Placental Malaria

BackgroundPlacental malaria (PM) is a leading cause of maternal and infant mortality. Although the accumulation of parasitized erythrocytes (PEs) and monocytes within the placenta is thought to contribute to the pathophysiology of PM, the molecular mechanisms underlying PM remain unclear. Based on the hypothesis that excessive complement activation may contribute to PM, in particular generation of the potent inflammatory peptide C5a, we investigated the role of C5a in the pathogenesis of PM in vitro and in vivo.Methodology and Principal FindingsUsing primary human monocytes, the interaction between C5a and malaria in vitro was assessed. CSA- and CD36-binding PEs induced activation of C5 in the presence of human serum. Plasmodium falciparum GPI (pfGPI) enhanced C5a receptor expression (CD88) on monocytes, and the co-incubation of monocytes with C5a and pfGPI resulted in the synergistic induction of cytokines (IL-6, TNF, IL-1β, and IL-10), chemokines (IL-8, MCP-1, MIP1α, MIP1β) and the anti-angiogenic factor sFlt-1 in a time and dose-dependent manner. This dysregulated response was abrogated by C5a receptor blockade. To assess the potential role of C5a in PM, C5a plasma levels were measured in malaria-exposed primigravid women in western Kenya. Compared to pregnant women without malaria, C5a levels were significantly elevated in women with PM.Conclusions and SignificanceThese results suggest that C5a may contribute to the pathogenesis of PM by inducing dysregulated inflammatory and angiogenic responses that impair placental function.

CD36 T188G gene polymorphism and severe falciparum malaria in India

Sequestration of parasitized erythrocytes (PE) in the microvasculature contributes directly to the virulence and severe pathology of Plasmodium falciparum malaria. The scavenger receptor CD36 appears to play an important role in PE adherence. Recently several mutations in the CD36 gene have been found to be associated with variability in susceptibility to P. falciparum infection in different ethnic populations. We investigated the possible association of T188G CD36 gene polymorphism with severe clinical manifestations of malaria in 95 adult patients with severe malaria admitted to SCB Medical College Hospital, Cuttack, Orissa, India ('severe' group) and 95 ethnically matched controls attending outpatient clinics at primary health centres ('mild' group). The frequency of the wild-type (T188T) allele of the CD36 gene was 0.91 in the 'severe' group and 0.78 in the 'mild' group of patients, while mutant (T188G) allele frequency was 0.09 in the severe group and 0.22 in the mild group. The Hardy-Weinberg equation indicates that the mutant allele is under selection pressure and disease association analysis shows that the presence of the heterozygote mutant allele renders protection against severe malaria (chi(2)=10.67, odds ratio=3.51, 95% CI 1.67-7.36).

STIMULATION OF TOLL-LIKE RECEPTOR 2 BY PLASMODIUMFALCIPARUM GLYCOSYLPHOSPHATIDYLINOSITOLS ENHANCES MACROPHAGE INTERNALIZATION OF PARASITIZED AND UNINFECTED ERYTHROCYTES

Background: Toll-like receptors (TLRs) are highly conserved innate sensing receptors that activate host defenses upon detection of microbial products. Plasmodium falciparum glycosylphosphatidylinositols (PfGPI) have been shown to stimulate macrophage cytokine production via TLR2. In addition to their role in inflammation, TLRs may also regulate phagocytosis. P. falciparum parasitized erythrocytes (PEs) can be non-opsonically internalized by macrophages in a process predominantly mediated by scavenger receptor CD36. Moreover, uninfected erythrocytes (UEs) are rendered susceptibleto macrophage clearance during malaria infection due to surface modifications, and this is believed to contribute to the pathogenesis of severe malarialanemia. We hypothesized that stimulation of macrophage TLR2 by PfGPI would enhance innate clearance of PEs as well as malaria-exposed UEs. Methods: Primaryhuman and murine macrophages were pre-stimulated with PfGPI or asynthetic TLR2 agonist (FSL-1) and phagocytosis assays were performed using P.falciparum PEs, EBABs (PE modelconsisting of anti-CD36 antibodies conjugated to human erythrocytes), IgG-opsonized PEs, and malaria-exposed UEs. Results: PfGPI and FSL-1 pre-stimulation significantly increased uptake of EBABs and P.falciparum PEs in a TLR2-dependent manner. TLR2 stimulation modestly increased Fc-mediated phagocytosis of IgG-opsonized PEs, and enhanced phagocytosis of UEs isolated from P. falciparum culture. Conclusion: TLR2-mediated macrophage activation enhanced in vitro clearance of both PEs and malaria-exposed UEs. These data underscore the complexity of TLR involvement in malaria infection: TLR-enhanced phagocytosis may benefit infected individuals by decreasing parasite burden, but in other contexts may predispose to anemia by enhancing UE destruction. Therapeutic targeting of TLR pathways in malaria requires careful consideration.

A new model for hemoglobin ingestion and transport by the human malaria parasite Plasmodium falciparum.

The current model for hemoglobin ingestion and transport by intraerythrocytic Plasmodium falciparum malaria parasites shares similarities with endocytosis. However, the model is largely hypothetical, and the mechanisms responsible for the ingestion and transport of host cell hemoglobin to the lysosome-like food vacuole (FV) of the parasite are poorly understood. Because actin dynamics play key roles in vesicle formation and transport in endocytosis, we used the actin-perturbing agents jasplakinolide and cytochalasin D to investigate the role of parasite actin in hemoglobin ingestion and transport to the FV. In addition, we tested the current hemoglobin trafficking model through extensive analysis of serial thin sections of parasitized erythrocytes (PE) by electron microscopy. We find that actin dynamics play multiple, important roles in the hemoglobin transport pathway, and that hemoglobin delivery to the FV via the cytostomes might be required for parasite survival. Evidence is provided for a new model, in which hemoglobin transport to the FV occurs by a vesicle-independent process.

Innate inflammatory and phagocytic responses to Plasmodium falciparum: linked processes or molecularly discrete pathways?s

Background: Effective innate immune responses are important for control of malaria blood-stage infection and in preventing progression to severe malaria in non-immune individuals. Key innate defenses include a tightly regulated inflammatory response and host clearance of parasitized erythrocytes (PE). Pattern recognition receptors on macrophages mediate these processes: parasite glycosylphosphatidylinositol (GPI) activates TLR2 to induce inflammation – an excess of which is associated with severe malaria – while scavenger receptor CD36 mediates non-opsonic uptake of PEs. Both pathways are potential therapeutic targets, but it is unclear whether they are interdependent. Findings in other systems implicate CD36 in inflammation and TLR2 in phagocytosis, and recent evidence indicates that CD36 and TLR2 can directly cooperate. 
 Methods: We investigated whether the innate inflammatory and phagocytic responses of macrophages to P. falciparum are separable: does CD36-mediated PE internalization have inflammatory outcomes, and does TLR2 regulate PE uptake? CD36-mediated endocytosis failed to induce TNFα production. As a more representative model of innate PE uptake, α-CD36 EBABs (Erythrocyte-Biotin-Avidin-Biotinylated antibody) were generated; macrophages internalized EBABs in a CD36-specific manner via a signaling pathway similar to that of PE uptake. 
 Results: Compared to controls, neither PE nor EBAB internalization induced TNFα release, indicating that the inflammatory consequences of CD36 engagement are ligand dependent. Regarding TLR2 regulation of PE uptake, wild type and Tlr2-/- macrophages showed no differences in EBAB or PE uptake. Pre-treatment of macrophages with P. falciparum GPI enhanced EBAB internalization, but this effect was CD36-independent and generalizable to other TLR ligands. 
 Conclusions: These results suggest that innate inflammatory and phagocytic responses of macrophages to malaria are discrete. Thus, therapeutic augmentation of CD36-mediated PE uptake should not exacerbate inflammation, nor should inhibition of the TLR2 pathway compromise CD36-mediated PE clearance. The role of TLR-enhanced internalization in malaria will be further examined.

HIV Impairs Opsonic Phagocytic Clearance of Pregnancy-Associated Malaria Parasites

BackgroundPrimigravid (PG) women are at risk for pregnancy-associated malaria (PAM). Multigravid (MG) women acquire protection against PAM; however, HIV infection impairs this protective response. Protection against PAM is associated with the production of IgG specific for variant surface antigens (VSA-PAM) expressed by chondroitin sulfate A (CSA)-adhering parasitized erythrocytes (PEs). We hypothesized that VSA-PAM-specific IgG confers protection by promoting opsonic phagocytosis of PAM isolates and that HIV infection impairs this response.Methods and FindingsWe assessed the ability of VSA-PAM-specific IgG to promote opsonic phagocytosis of CSA-adhering PEs and the impact of HIV infection on this process. Opsonic phagocytosis assays were performed using the CSA-adherent parasite line CS2 and human and murine macrophages. CS2 PEs were opsonized with plasma or purified IgG subclasses from HIV-negative or HIV-infected PG and MG Kenyan women or sympatric men. Levels of IgG subclasses specific for VSA-PAM were compared in HIV-negative and HIV-infected women by flow cytometry. Plasma from HIV-negative MG women, but not PG women or men, promoted the opsonic phagocytosis of CSA-binding PEs (p < 0.001). This function depended on VSA-PAM-specific plasma IgG1 and IgG3. HIV-infected MG women had significantly lower plasma opsonizing activity (median phagocytic index 46 [interquartile range (IQR) 18–195] versus 251 [IQR 93–397], p = 0.006) and levels of VSA-PAM-specific IgG1 (mean fluorescence intensity [MFI] 13 [IQR 11–20] versus 30 [IQR 23–41], p < 0.001) and IgG3 (MFI 17 [IQR 14–23] versus 28 [IQR 23–37], p < 0.001) than their HIV-negative MG counterparts.ConclusionsOpsonic phagocytosis may represent a novel correlate of protection against PAM. HIV infection may increase the susceptibility of multigravid women to PAM by impairing this clearance mechanism.

Placental Chondroitin Sulfate A–Binding Malarial Isolates Evade Innate Phagocytic Clearance

Pregnancy-associated malaria is characterized by the accumulation of parasitized erythrocytes (PEs) and monocytes in the placenta, and they are believed to directly contribute to adverse birth outcomes. Although most parasite isolates adhere to CD36, placental isolates express novel variant surface antigens (VSAs) and bind to chondroitin sulfate A (CSA). CSA-binding PEs are rarely observed outside of pregnancy, and most primigravid women lack immunity and must rely on innate immune mechanisms to clear these placental parasite variants. We hypothesized that differences in VSA expression and adhesive phenotype between pregnancy-associated (CSA-binding) and non-pregnancy-associated (CD36-binding) isolates may have direct implications for the failure of primigravid women to control the placental parasite burden through innate phagocytic pathways. We demonstrate here, both in vitro and in vivo, that there is a nonopsonic phagocytic defect for CSA-binding PEs. The ability of CSA-binding PEs to evade innate clearance pathways may contribute to the parasite accumulation and recruitment of monocytes that characterize placental malaria.

EX VIVO AND IN VITRO IMPAIRMENT OF CD36 EXPRESSION AND TUMOR NECROSIS FACTOR-α PRODUCTION IN HUMAN MONOCYTES IN RESPONSE TO PLASMODIUM FALCIPARUM–PARASITIZED ERYTHROCYTES

Severe malaria is associated with the failure of host defenses to control parasite replication, with the excessive secretion of proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), and with the sequestration of parasitized erythrocytes (PEs) in the microcirculation of vital organs. The scavenger receptor CD36, known as a major sequestration receptor, has also been identified as an important factor in mediating nonopsonic phagocytosis of PEs by monocytes and macrophages. The specific consequence of this phagocytosis is a decrease in parasite-induced TNF-alpha secretion. We evaluated the variations in CD36 level and in lipopolysaccharide (LPS)-induced TNF-alpha production in monocytes from Plasmodium falciparum-infected patients and in vitro in the presence of PEs. Both the monocytes from infected patients and from in vitro culture showed a decrease of CD36 expression and a reduced production of TNF-alpha induced by LPS. Using incubation assays with no contact between monocytes and PEs, or in the presence of a soluble supernatant obtained from the incubation of monocytes and PEs, this study shows that decreased CD36 expression was posttranscriptional and not directly related to PEs phagocytosis. In addition, these culture models suggest that the reduced capacity of TNF-alpha production occurred in 2 phases. The early phase (24 hr) appeared to be CD36 dependent and the second phase (48 hr) was due to a soluble factor produced by PEs. These observations suggest that the control of the TNF-alpha production in malaria by monocytes was not entirely dependent on the phagocytosis of PEs by CD36 and that soluble factors produced by PEs could play a role in this process.

Identification of a 67-amino-acid region of the Plasmodium falciparum variant surface antigen that binds chondroitin sulphate A and elicits antibodies reactive with the surface of placental isolates.

The complications of malaria in pregnancy are caused by the massive sequestration of parasitized erythrocytes (PE) in the placenta. Placental isolates of Plasmodium falciparum are unusual in that they do not bind the primary microvasculature receptor CD36 but instead bind chondroitin sulphate A (CSA). Pregnant mothers develop antibodies that recognize placental variants worldwide, suggesting that a vaccine against malaria in pregnancy is possible. Some members of the Duffy binding-like gamma (DBL-gamma) domain of the large and diverse P. falciparum erythrocyte membrane protein-1 (PfEMP-1) family, when expressed on Chinese hamster ovary (CHO) cells, bind CSA. To characterize better the molecular requirements for DBL-gamma adhesion to CSA, we determined the binding of various DBL-gamma domains. Most DBL-gamma did not bind CSA, and no conserved region was identified that strictly differentiated binders from non-binders. Structure-function analysis of the FCR3-CSA DBL-gamma domain localized the minimal CSA binding region to a 67-residue fragment. This region was partially conserved among some binding sequences. Serum from a rabbit immunized with the minimal domain reacted with CSA-binding parasite lines, but not with non-CSA-adherent PE lines that adhered to CD36 and other receptors. The identification of a minimal binding region from a highly variable cytoadherent family may have application for a vaccine against malaria in pregnancy.

INHIBITORY ACTIVITIES OF SULFATED PROTEOGLYCANS ON CHONDROITIN SULFATE A-MEDIATED CYTOADHERENCE OF PLASMODIUM FALCIPARUM ISOLATES FROM THAILAND

Chondroitin sulfate A (CSA) is an important receptor for Plasmodium falciparum-infected erythrocytes in the placenta. To study the molecular interaction between parasitized erythrocytes (PE) to CSA, we performed in vitro cytoadherence inhibition assays of PE infected with wild and laboratory isolates of P. falciparum to CSA using various glycosaminoglycans (GAGs). Marked decrease in PE adhesion to immobilized CSA and CSA-expressed cells was achieved with soluble chondroitin sulfate D (CSD) and chondroitin sulfate E (CSE) at low concentrations. The effect was dose dependent with the degree of inhibition exceeded that of soluble CSA in certain clinical isolates. The results suggested the influence of oversulfation of CS variant chains on PE adherence to CSA. Interestingly, PE of the tested wild isolates could adhere to immobilized CSD and CSE at different levels while PE of CSA-selected laboratory lines could not. Partial inhibitory activity was observed when chondroitin sulfate C (CSC), chondroitin sulfate B (CSB), and polyolpolysulfate were used even at high concentrations. Keratan sulfate, colominic acid, and Suramine were unable to inhibit PE adherence. Taken together, the results confirm that the 4-sulfate amino sugar moiety, as well as the basic disaccharide structure of N-acetylgalactosamine linked to glucuronic acid, may influence the degree of this molecular interaction. However, other sulfation patterns that could influence the interaction could not be overlooked, as in the case of CSD which contains 2-O-sulfation at glucuronic acid. Studies using pentosan polysulfate, an oversulfated molecule with a xylan backbone, as an inhibitor also showed a reduction of PE adherence of most isolates tested. Thus, only the sulfate content and pattern of this molecule could affect the adhesive interactions. In addition, difference in capacity of low molecular weight heparins to inhibit CSA-mediated PE cytoadherence of clinical isolates was also observed, thereby providing evidence on the heterogeneity in cytoadherence characteristics of maternal parasite isolates as well as their therapeutic potentials.

Comparisons of the resistance to Japanese theileriosis among Santa Gertrudis × Japanese Shorthorn F1, Japanese Shorthorn and their reciprocal crosses

ABSTRACTTo improve the resistance of Japanese Shorthorn (JS) calves to the hemoprotozoan parasite Theileria sergenti (Ts), Santa Gertrudis (SG) × JS F1 and its reciprocal backcross (F1 × JS and JS × F1) calves were produced. All the calves were born from February to April and kept on pasture with their dams from May to October. Blood samples were collected biweekly until 18 weeks of grazing and two indices of resistance to the parasite, percentage of parasitized erythrocytes (PE) and hematocrit value (Ht) were monitored. There was a weak negative correlation between daily gain (DG) on pasture and the average PE (P &lt; 0.1), and was a significantly positive correlation between DG on pasture and the average Ht (P &lt; 0.01) in the experimental period. Although maximum PE observed at six or eight weeks of grazing period was not significantly different among the four mating types, SG × JS F1 calves exhibited a significantly larger decrease in PE compared to purebred JS after the peak PE. F1 calves also showed maximum Ht through the grazing period. There were no apparent differences in the two indices among the two reciprocal backcrosses and purebred JS. These results indicated that Ts infection and subsequent decrease in Ht affected the DG of calves in the grassland. The present study also demonstrated that the introduction of the SG gene into JS was effective at the F1 level in regard to the resistance to theileriosis, and that in the backcrosses an improvement in resistance could not be expected.

DNA immunization with the cysteine-rich interdomain region 1 of the Plasmodium falciparum variant antigen elicits limited cross-reactive antibody responses.

The variant surface antigens of Plasmodium falciparum are an important component of naturally acquired immunity and an important vaccine target. However, these proteins appear to elicit primarily variant-specific antibodies. We tested if naked DNA immunization can elicit more cross-reactive antibody responses and allow simultaneous immunization with several variant constructs. Mice immunized with plasmid DNA expressing variant cysteine-rich interdomain region 1 (CIDR1) domains of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) developed antibodies that were reactive to the corresponding PfEMP1s as measured by an enzyme-linked immunosorbent assay, flow cytometry, and agglutination of parasitized erythrocytes (PEs). We observed some cross-reactive immune responses; for example, sera from mice immunized with one domain agglutinated PEs of various lines and recognized heterologous domains expressed on the surface of Chinese hamster ovary (CHO) cells. We found no significant antigenic competition when animals were immunized with a mixture of plasmids or immunized sequentially with individual constructs. Moreover, mixed or sequential immunizations resulted in greater cross-reactive agglutination responses than immunization with a single domain. Recombinant protein (Sc y179) immunization after priming with DNA (prime-boost regimen) increased antibody titers to the homologous domain substantially but seemed to diminish the cross-reactive responses somewhat. The titer of agglutinating antibodies was previously shown to correlate with protection. Surprisingly, the agglutination titers of sera from DNA immunization were high, similar to those of pooled human hyperimmune sera. These sera also appeared to give limited low-titer variant transcending agglutination. Thus, DNA immunization appears to be a very useful tool for developing variant antigen vaccines.

Induction of HO-1 in tissue macrophages and monocytes in fatal falciparum malaria and sepsis

BackgroundAs well as being inducible by haem, haemoxygenase -1 (HO-1) is also induced by interleukin-10 and an anti-inflammatory prostaglandin, 15d PGJ2, the carbon monoxide thus produced mediating the anti-inflammatory effects of these molecules. The cellular distribution of HO-1, by immunohistochemistry, in brain, lung and liver in fatal falciparum malaria, and in sepsis, is reported.MethodsWax sections were stained, at a 1:1000 dilution of primary antibody, for HO-1 in tissues collected during paediatric autopsies in Blantyre, Malawi. These comprised 37 acutely ill comatose patients, 32 of whom were diagnosed clinically as cerebral malaria and the other 5 as bacterial diseases with coma. Another 3 died unexpectedly from an alert state. Other control tissues were from Australian adults.ResultsApart from its presence in splenic red pulp macrophages and microhaemorrhages, staining for HO-1 was confined to intravascular monocytes and certain tissue macrophages. Of the 32 clinically diagnosed cerebral malaria cases, 11 (category A) cases had negligible histological change in the brain and absence of or scanty intravascular sequestration of parasitized erythrocytes. Of these 11 cases, eight proved at autopsy to have other pathological changes as well, and none of these eight showed HO-1 staining within the brain apart from isolated moderate staining in one case. Two of the three without another pathological diagnosis showed moderate staining of scattered monocytes in brain vessels. Six of these 11 (category A) cases exhibited strong lung staining, and the Kupffer cells of nine of them were intensely stained. Of the seven (category B) cases with no histological changes in the brain, but appreciable sequestered parasitised erythrocytes present, one was without staining, and the other six showed strongly staining, rare or scattered monocytes in cerebral vessels. All six lung sections not obscured by neutrophils showed strong staining of monocytes and alveolar macrophages, and all six available liver sections showed moderate or strong staining of Kupffer cells. Of the 14 (category C) cases, in which brains showed micro-haemorrhages and intravascular mononuclear cell accumulations, plus sequestered parasitised erythrocytes, all exhibited strong monocyte HO-1 staining in cells forming accumulations and scattered singly within cerebral blood vessels. Eleven of the available and readable 13 lung sections showed strongly staining monocytes and alveolar macrophages, and one stained moderately. All of the 14 livers had strongly stained Kupffer cells. Of five cases of comatose culture-defined bacterial infection, three showed a scattering of stained monocytes in vessels within the brain parenchyma, three had stained cells in lung sections, and all five demonstrated moderately or strongly staining Kupffer cells. Brain sections from all three African controls, lung sections from two of them, and liver from one, showed no staining for HO-1, and other control lung and liver sections showed few, palely stained cells only. Australian-origin adult brains exhibited no staining, whether the patients had died from coronary artery disease or from non-infectious, non-cerebral conditionsConclusionsClinically diagnosed 'cerebral malaria' in children includes some cases in whom malaria is not the only diagnosis with the hindsight afforded by autopsy. In these patients there is widespread systemic inflammation, judged by HO-1 induction, at the time of death, but minimal intracerebral inflammation. In other cases with no pathological diagnosis except malaria, there is evidence of widespread inflammatory responses both in the brain and in other major organs. The relative contributions of intracerebral and systemic host inflammatory responses in the pathogenesis of coma and death in malaria deserve further investigation.

Peroxisome proliferator-activated receptor gamma-retinoid X receptor agonists increase CD36-dependent phagocytosis of Plasmodium falciparum-parasitized erythrocytes and decrease malaria-induced TNF-alpha secretion by monocytes/macrophages.

Severe and fatal malaria is associated with the failure of host defenses to control parasite replication, excessive secretion of proinflammatory cytokines such as TNF-alpha, and sequestration of parasitized erythrocytes (PEs) in vital organs. The identification of CD36 as a major sequestration receptor has led to the assumption that it contributes to the pathophysiology of severe malaria and has prompted the development of antiadherence therapies to disrupt the CD36-PE interaction. This concept has been challenged by unexpected evidence that individuals deficient in CD36 are more susceptible to severe and cerebral malaria. In this study, we demonstrate that CD36 is the major receptor mediating nonopsonic phagocytosis of PEs by macrophages, a clearance mechanism of potential importance in nonimmune hosts at the greatest risk of severe malaria. CD36-mediated uptake of PEs occurs via a novel pathway that does not involve thrombospondin, the vitronectin receptor, or phosphatidylserine recognition. Furthermore, we show that proliferator-activated receptor gamma-retinoid X receptor agonists induce an increase in CD36-mediated phagocytosis and a decrease in parasite-induced TNF-alpha secretion. Specific up-regulation of monocyte/macrophage CD36 may represent a novel therapeutic strategy to prevent or treat severe malaria.