Safety and immunogenicity of a Plasmodium vivax sporozoite vaccine.

A recombinant DNA Plasmodium vivax sporozoite vaccine containing the repeating region of the Salvador I strain circumsporozoite (CS) protein was produced in Escherichia coli. This vaccine was tested in 13 naive volunteers at doses of 10-1,000 micrograms. No serious adverse reactions were noted. None of 4 volunteers receiving the 10 micrograms dose developed antibodies measurable by ELISA. Six of 9 volunteers in the other dose groups developed measurable antibodies: 5 of 5 volunteers receiving 100 micrograms and 1 of 4 receiving 1,000 micrograms. Antibody responses measured by immunofluorescence assays paralleled those seen by ELISA. None of the volunteers developed antisera that inhibited sporozoite invasion of human hepatoma cells in vitro. Lack of a classical anamnestic response and lack of a typical dose response to increasing amounts of antigen suggests the possible presence of an immunosuppressive epitope in the repetitive region of the CS protein.     

Safety and immunogenicity of a recombinant sporozoite malaria vaccine against Plasmodium vivax.

A recombinant Plasmodium vivax circumsporozoite (CS) antigen representing approximately 70% of the CS protein was expressed in yeast and adsorbed onto aluminum hydroxide for use as a malaria vaccine. In a study of safety and immunogenicity, 30 volunteers were divided into four groups of 5, 5, 10, and 10 individuals, and inoculated intramuscularly with 50, 100, 200, or 400 micrograms of vaccine, respectively. Primary vaccinations were followed by two booster immunizations at six weeks and six months. Overall, the vaccine was well tolerated. Following the third vaccination, one volunteer developed acute hepatitis of uncertain etiology that resolved without sequelae. All volunteers in the 400-micrograms group, and six of 10 in the 200-micrograms group generated IgG against P. vivax CS protein, as determined by Western blot using recombinant CS protein. However, the magnitude of the antibody response measured by indirect immunofluorescence of intact sporozoites or enzyme-linked immunosorbent assay against the recombinant protein was low, and responses could not be boosted. Antigen-driven replication studies using peripheral blood lymphocytes failed to detect proliferative responses specific to peptide sequences represented in the recombinant vaccine, except in one volunteer. Minimal humoral and cell-mediated immune responses developed in most recipients who received this recombinant CS vaccine.     

间日疟原虫抗原体外诱导间日疟患者PBMC凋亡的研究

目的分析间日疟原虫抗原(PvAg)诱导宿主外周血单个核细胞(PBMC)的凋亡水平方法采用流式细胞术结合应用膜联蛋白-V(Annexin-V),测定7例间日疟现症感染者PBMC经PvAg刺激后CD4+T细胞、CD8+T细胞及CD19+B细胞的凋亡率,并与空白对照组比较。结果经PvAg刺激后的间日疟现症感染者CD19+B细胞及CD4+T细胞凋亡率分别为7.26%和48.08%,与空白对照凋亡率4.08%和22.80%比较差异无统计学意义(P>0.05);CD8+T细胞凋亡率为55.16%,与对照凋亡率22.86%比较差异有统计学意义(P<0.05)。结论 PvAg可诱导间日疟现症感染者CD8+T细胞凋亡,从而可能参与介导间日疟原虫发生免疫逃逸。     

间日疟原虫和恶性疟原虫可溶性抗原免疫反应性比较

目的分析和比较间日疟原虫(Plasmodiumvivax,P.v)和恶性疟原虫(P.falciparum,P.f)可溶性抗原与间日疟感染者混合血清和单克隆抗体(McAb)M26-32免疫反应性的差别,以期寻找潜在的疟疾诊断抗原。方法取P.v感染者血样,用Plasmodipur滤器分离去除白细胞,经60%Percoll浓集其中的感染红细胞(i RBC)。分别制备P.v、P.f和正常红细胞(nRBC)可溶性抗原,应用P.v感染者、正常对照混合血清和M26-32单抗与相应的抗原进行免疫印迹分析。结果免疫印迹分析表明,P.v感染者能特异性识别26k、33、49、115kDaP.v抗原;100、102、110、150、175kDaP.f抗原;能够交叉识别的条带有:31、59、63、70、120kDa。M26-32单抗能识别P.f、P.v抗原中31kDa等抗原条带。结论P.v感染者能特异识别间日疟抗原组份,并能交叉识别P.f抗原,其中31kDa抗原组分具有较强的免疫原性,同时能被M26-32单抗识别,其作为P.v特异性诊断抗原的价值有待于进一步研究。     

A blood stage antigen of Plasmodium falciparum shares determinants with the sporozoite coat protein.

A cDNA clone expressing a Plasmodium falciparum blood-stage antigen in Escherichia coli was identified by colony immunoassay using immune human sera. Antibodies affinity-purified on extracts of this clone reacted with both asexual blood stages and sporozoites of P. falciparum, recognizing a Mr23,000 protein in the blood stages. The nucleotide sequence of the cDNA revealed a signal peptide and an internal hydrophobic sequence typical of transmembrane anchor sequences. Located 3' to the putative anchor are two tetramers, Asn-Ala-Asn-Pro and Asn-Ala-Asp-Pro, which are closely related to the repeats of the circumsporozoite protein of P. falciparum. The blood stage protein is conserved amongst several isolates of P. falciparum, and antibodies against it are common in the sera of individuals living in the area where the parasite is endemic.     

Widespread reactivity of human sera with a variant repeat of the circumsporozoite protein of Plasmodium vivax

A panel of Brazilian and Indian sera was screened for reactivity with a variant strain of Plasmodium vivax recently isolated in Thailand. This strain has been shown to have a unique repeat region which differs from the previously described P. vivax CS proteins. A total of 21/343 human sera were found to react with a synthetic peptide representing the variant P. vivax repeat. All of the sera that reacted with the variant repeat peptide, (ANGAGNQPG)4, also reacted with variant P. vivax sporozoites. Both the anti-peptide and the antisporozoite reactivity were totally abolished by adsorption with the variant peptide. Some of the human sera contained variant antibodies that were species specific and could only be adsorbed with the specific variant peptide. These findings suggest that the variant strain of P. vivax might have a worldwide distribution. We also found that some of the variant positive sera reacted with P. brasilianum sporozoites and with the P. brasilianum/P. malariae CS repeat. The adsorption of these sera with the P. brasilianum/P. malariae repeat peptide, (NAAG)4, significantly reduced the reactivity of these sera with the P. vivax variant. In addition, polyclonal and monoclonal antibodies of mice immunized with P. brasilianum sporozoites cross-reacted with the variant P. vivax CS. These findings suggest that exposure to P. brasilianum or P. malariae may give rise to sporozoite antibodies which cross-react with the P. vivax variant CS.     

Plasmodium vivax sporozoite antibodies in individuals exposed during a single malaria outbreak in a non-endemic area

We studied seroreactivity against Plasmodium vivax antigens in 62 individuals living in a small community near Mantena, Minas Gerais, Brazil, an area outside the endemic malaria zone Brazil. Eight months earlier, there had been transmission of P. vivax for a period of 50 days, which was then totally controlled by chemotherapy and insecticides. An anti-sporozoite response, measured by ELISA using a recombinant protein expressed in yeast, was detected in 45% (14 of 31) of individuals eight months after infection and persisted for 20 months in 12%. Eighteen individuals were treated prophylactically for malaria because they lived in houses in which an overt infection had occurred. Seven of these individuals were ELISA positive; of these, 5 had antibodies against the blood stage parasites. Among 13 other individuals in the endemic area who did not have positive smears, had not been ill, and had not received prophylaxis, five were anti-circumsporozoite positive up to a 40-fold serum dilution. They did not develop asexual blood stage antibodies and remained parasite-free for the following 20 months.     

Recognition of Plasmodium falciparum asexual stage antigens by antibodies in sera from people exposed to Plasmodium vivax.

An analysis of Plasmodium falciparum antigen-specific antibodies was performed on 44 serum samples from Guatemala, a region endemic for P. vivax. Most sera showed positive reactivity to P. falciparum asexual stage antigens by indirect immunofluorescent assay, enzyme-linked immunosorbent assay, and immunoprecipitation analysis using biosynthetically labeled parasites. Although several antigens were recognized by these sera, proteins with molecular weights of 195 kD, 140 kD, and in the range of 70-80 kD were strongly recognized by many of the sera studied. No such reactivity was observed for any of the surface antigens in the male and female gametes and zygotes of P. falciparum. These studies suggest that P. vivax and P. falciparum, two major human parasites, may share certain epitopes in several antigens of immunologic significance.     

间日疟原虫环子孢子蛋白和裂殖子表面抗原的多态性

虽然恶性疟原虫疫苗抗原研究取得了较大进展，目前已制备出许多恶性疟原虫期特异性抗原［１］，但间日疟原虫的研究因不能体外培养而受限制。本文将主要描述至今已特征化了的两种间日疟原虫候选疫苗抗原：环子孢子蛋白和裂殖子表面抗原－１。为了资料的完整性和选择性，本...     

Cellular immune responses to recombinant Plasmodium vivax tryptophan-rich antigen (PvTRAg) among individuals exposed to vivax malaria

Plasmodium vivax , the most widespread species of human malaria parasite responsible for 70–80 million cases each year requires a vaccine. In recent years, many potential vaccine candidate antigens have been identified from P. vivax including PvTRAg. We describe here cellular immune response to recombinant PvTRAg expressed in Escherichia coli . The in vitro stimulation of PBMCs derived from P. vivax -exposed individuals ( n  = 16) showed strong proliferative response (SI > 2·2) to PvTRAg as compared to PBMCs from normal healthy controls ( n  = 8). Although both Th1 (IFN-γ, TNF-α and IL-12) and Th2 (IL-4 and IL-10) cytokines were secreted by the PBMCs of the P. vivax -exposed individuals in response to PvTRAg, the overall response was more inclined towards Th2. In conclusion, recombinant PvTRAg was found to elicit strong cellular immune response among the P. vivax -exposed individuals.     

间日疟原虫抗药性研究进展

疟疾作为一种致死性很高的全球性寄生虫病,一直被全世界所关注,疟疾的控制也被列入全球三大公共卫生问题之一。由于疟疾抗药性的流行和蔓延,尤其是间日疟抗性的快速传播,使得疟原虫抗性的检测、预测以及新药的研发成为当前研究重点。针对这一系列问题,本文对当前间日疟抗药性检测方法、分子机理以及热点抗间日疟药物做一综述。     

Quantitative determination of sporozoites and circumsporozoite antigen in mosquitoes infected with Plasmodium falciparum or P. vivax

It is essential for malariologists and researchers to have simple and accurate means of assessing the threat of Plasmodium parasites. An attempt was therefore made to re-standardize one of the circumsporozoite (CS) ELISA that can be used to detect and quantify the circumsporozoite antigens of P. falciparum and P. vivax. A two-site, 'sandwich' ELISA based on a monoclonal antibody was used to test for the CS antigen and sporozoites of each Plasmodium species simultaneously. Using the resultant optical-density values, standard curves, that permit the number of sporozoites in an infected mosquito to be estimated from the quantification of the CS antigen, were constructed. Using these plots and the CS ELISA, the presence of just 12.5 sporozoites (i.e. 0.8 pg CS antigen) of P. falciparum, four sporozoites (3.2 pg antigen) of P. vivax-210 or 12.5 sporozoites (32.0 pg antigen) of P. vivax-247 could be demonstrated.     

Primary structure of the merozoite surface antigen 1 of Plasmodium vivax reveals sequences conserved between different Plasmodium species.

Merozoite surface antigen 1 (MSA1) of several species of plasmodia has been shown to be a promising candidate for a vaccine directed against the asexual blood stages of malaria. We report the cloning and characterization of the MSA1 gene of the human malaria parasite Plasmodium vivax. This gene, which we call Pv200, encodes a polypeptide of 1726 amino acids and displays features described for MSA1 genes of other species, such as signal peptide and anchoring sequences, conserved cysteine residues, number of potential N-glycosylation sites, and repeats consisting here of 23 glutamine residues in a row. When the nucleotide and deduced amino acid sequences of the MSA1 of P. vivax are compared to those of another human malaria parasite, Plasmodium falciparum, and to those of the rodent parasite Plasmodium yoelii, 10 regions of high amino acid similarity are observed despite the very different dG + dC contents of the corresponding genes. All of the interspecies conserved regions reside within the conserved or semiconserved blocks delimited by the sequences of different alleles of the MSA1 gene of P. falciparum.     

Antibodies to Plasmodium vivax apical membrane antigen 1: persistence and correlation with malaria transmission intensity.

The antibody responses to the apical membrane antigen 1 of the Plasmodium vivax (PvAMA-1) were investigated in subjects living in areas of Brazil with different levels of malaria transmission. The prevalence and the levels of IgG to PvAMA-1 increased with the time of exposure. The frequency of a positive response and the mean IgG level were higher in areas where malaria prevalence was more intense, especially among non-infected subjects exposed to moderate transmission over a period of 20 years. The proportions and levels of IgG1and IgG3 isotypes were significantly higher among those subjects with long-term exposure. Antibodies, mainly IgG1, to PvAMA-1 persisted for seven years among subjects briefly exposed to malaria in an outbreak outside the Brazilian malaria-endemic area. These data show the highly immunogenic properties of PvAMA-1 and emphasize its possible use as a malaria vaccine candidate.     

Amplification of pvmdr1 associated with multidrug-resistant Plasmodium vivax

BACKGROUND: Multidrug-resistant strains of Plasmodium vivax are emerging in Southeast Asia. METHODS: In vitro drug susceptibility and pvmdr1 genotype were determined in P. vivax field isolates from Indonesia and Thailand. RESULTS: Increased pvmdr1 copy number was present in 21% of isolates from Thailand (15/71) and none from Indonesia (0/114; P < .001). Compared with Indonesian isolates, the median IC(50) of Thai isolates was lower for chloroquine (36 vs. 114 nmol/L; P < .001) but higher for amodiaquine (34 vs. 13.7 nmol/L; P = .032), artesunate (8.33 vs. 1.58 nmol/L; P < .001), and mefloquine (111 vs. 9.87 nmol/L; P < .001). In 11 cryopreserved Thai isolates, those with increased pvmdr1 copy number had a higher IC(50) for mefloquine (78.6 vs. 38 nmol/L for single-copy isolates; P = .006). Compared with isolates with the wild-type allele, the Y976F mutation of pvmdr1 was associated with reduced susceptibility to chloroquine (154 nmol/L [range, 4.6-3505] vs. 34 nmol/L [range, 6.7-149]; P < .001) but greater susceptibility to artesunate (1.8 vs. 9.5 nmol/L; P = .009) and mefloquine (14 vs. 121 nmol/L; P < .001). CONCLUSIONS: Amplification of pvmdr1 and single-nucleotide polymorphisms are correlated with susceptibility of P. vivax to multiple antimalarial drugs. Chloroquine and mefloquine appear to exert competitive evolutionary pressure on pvmdr1, similar to that observed with pfmdr1 in Plasmodium falciparum.     

Atypical manifestations of Plasmodium vivax malaria

About 110 patients were enrolled to study the atypical presentations and the chloroquine sensitivity pattern of Plasmodium vivax malaria. The diagnosis was made from Giemsa stained peripheral blood smear. The co-infection of falciparum malaria was excluded both by smear and ParaSight F-test. After a thorough clinical work up, biochemical investigations were done. The fever clearance and parasite clearance time were determined in all cases. Absence of malarial paroxysm (22.8 per cent), migrainous headache (4.5 per cent), myalgia (6.3 per cent), episodic urticarial rash (1.8 per cent), relative bradycardia (13.6 per cent) and postural hypotension (2.7 per cent) were the atypical manifestations encountered. Besides this, severe forms like jaundice (7.2 per cent), cerebral involvement (0.9 per cent), severe anaemia (7.2 per cent), thrombocytopenia (3.6 per cent) and pancytopenia (0.9 per cent) had been detected. All, except the patient with cerebral involvement were treated with chloroquine patients responded well to the treatment except two (1.8 per cent) patients who had chloroquine resistance. This study showed that vivax malaria can present with atypical and protean manifestations. The changing clinical profile along with development of chloroquine resistance may be considered as a warning signal.