我国间日疟原虫混合流行区分离株Dufry抗原结合蛋白基因多态性分析

为了解我国季节混合流行区云南省间日疟原虫红内期候选抗原Dufly抗原结合蛋白（DBP）基因多态性特点,提取19株我国云南株疟原虫基因组DNA,PCR扩增DBPRⅡ区基因片段。以SalI标准株作为参照,对所获得的基因序列进行排序分析,检测基因突变位点,以中性检验分析评估序列多态性。结果表明,中国间日疟原虫混合流行区云南分离株PvDBPRII的基因多态性与南美、中非等流行突变位点一致,未发现地区特异性的突变位点,但与国内单一流行区湖北和浙江地区突变位点存在一定差异。原因可能为整体上受到自然选择的影响,呈正向选择趋势。上述结果可为以PvDBPRⅡ为基础建立有效传播阻断疫苗的研究提供一定的线索。     

恶性疟原虫FCCl／HN株MSAl全基因编码区的体外扩增

恶性疟原虫裂殖子表面蛋白1(MSA1)是抗疟疫苗的候选抗原之一。据已知的MSAl基因序列，自行设计合成了四对引物。应用PCR技术，分四段从恶性疟原虫FCC1／HN株基因组DNA中扩增出垒基因编码区序列。扩增产物经1．2％琼脂塘凝腔电泳鉴定．表明获得了正确的MSA1基因扩增片段。     

恶性疟原虫已糖转运体编码基因的体外扩增及克隆

目的：体外扩增恶性疟原虫海南分离株的已糖转运体基因(PfHT1)，并将该基因克隆至pEGFF真核表达载体内使其高效表达，为研究DNA疫苗创造条件。方法：特定PCR引物的设计；恶性疟原虫FCC1／HN株的体外培养；提取基因组DNA；PCR扩增和琼脂糖凝胶电泳分析；酶切、连接及PCR分析鉴定。结果：从恶性疟原虫簿南分离株基因组DNA中扩增出特异性的编码FfhTl的基因序列．片段太小为1516bp，克隆鉴定结果表明插人片段大小正确。结论：体外成功扩增出恶性疟原虫PfHTl编码序列，与预期长度相符，并成功构建pEGFF-Htl真核表达载体。为研究其结构、功能和免疫原性奠定基础，     

恶性疟原虫FCC—1／HN株环子孢子蛋白基因分枝杆菌——大肠杆穿梭表达重组质粒的构建及序列测定

本文对恶性疟原虫环子孢子蛋白(circumsporozoiteprotein,CSP)基因片段进行克隆和序列测定。根据恶性疟原虫837株基因编码序列设计合成一对引物,采用PCR技术从恶性疟原虫FCC-1/HN株基因组DNA中特异扩增CSP基因片段的Ⅰ区、中央重复区、重复区后可变区和Ⅱ区;经纯化的扩增产物用BamHⅠ和KpnⅠ双酶切后,定向克隆入大肠杆菌——分枝杆菌穿梭表达质粒,转化感受态大肠杆菌DH5α,重组克隆经抗性筛选和快速凝胶电泳鉴定,再经PCR和酶切鉴定,并对重组子进行序列测定。结果表明从恶性疟原虫FCC-1／HN株基因组DNA中可特异扩增出约1171bp的基因片段,阳性重组质粒经双酶切和PCR鉴定与预期的结果一致,序列测定表明所克隆的基因和编码环子孢子抗原的基因片段相符。     

缅甸流行区间日疟原虫Duffy结合蛋白的基因多态性和自然选择分析?

为明确缅甸流行区间日疟原虫红内期疫苗候选抗原Duffy结合蛋白(DBP)的基因多态性特点,提取20例缅甸流行区(Bilin和Paletwa)间日疟原虫基因组DNA,通过PCR扩增和测序检测,参考Mandalay流行区(缅甸)相应序列,对pvdbp-Ⅱ基因进行多态性分析。结果表明,各流行区pvdbp-Ⅱ基因的π值分别为0.002、0.009和0.002,且d_N/d_S均大于1。中性检验表明各流行区pvdbp-Ⅱ基因处于阳性选择;pvdbp-Ⅱ基因在Bilin和Mandalay流行区存在基因重组,各流行区群体间存在不同程度的遗传分化,H14是21种不同的单倍型中出现频率最高的单倍型。Pvdbp-Ⅱ基因存在多态并经历阳性选择,提示其作为红内期疫苗候选靶点;H14高频率的出现,提示以其为基础研制pvdbp-Ⅱ基因作为红内期疫苗候选抗原的可能性。     

恶性疟原虫丝氨酸重复抗原部分基因的克隆及其鉴定

根据恶心疟原虫丝氨酸重复抗原基因的保守序列。设计并合成了一对寡核苷酸引物，用PCR方法扩增恶性疟原虫云南株(PFD-3／YN）与海南株(FCC-1／HN)丝氨酸重复抗原部分基因片段．经基因序列测定后，将该片段用SmaI SaⅡ双酶消化，克隆于表达载体pR1T2T，并转化大肠杆菌N4830-1，用PCR及酶切法鉴定pR1T2T-SERA重组质业，为丝氨酸重复抗原的表达奠定基础。     

应用多聚酶链反应技术检测疟原虫的初步研究

根据编码恶性疟原虫(P．f)红细胞结合抗原(EBA-175)的部分DNA片段和间日疟原虫(P．v．)小亚基核糖体RNA基因序列设计合成恶性疟原虫和间日疟原虫的特异性引物各一对并进行多聚酶链反应(PCR)检测恶性疟和间日疟病人标本。扩增产物经琼脂糖电泳分析，可见在P．f.样本中扩增出特异的492bp大小的DNA片段，P．v．样本中扩增出特异的714bp大小的DNA片段。而在健康人血的白细胞、伯氏疟原虫样本和食触猴疟原虫样本中均不能扩增出以上片段。其结果与镜检符合率分别达95％和93.3％以上，表明该方法是一种特异、敏感的检测方法。     

恶性疟原虫裂殖子表面蛋白1羧基端编码基因真核表？…

构建以恶性疟原虫红内期重要的疫苗候选抗原－裂殖子表面蛋白羧基端编码分子量４２０００蛋白的基因片段为外源基因的可用作候选核酸疫苗的真核表达载体。方法目前对疟疾核酸疫苗的研究仅见于鼠疟，将恶性疟原虫ＦＵＰ株裂殖子表面蛋白１羧基端编码４２０００蛋白的基因片段用常规分子克隆方法，分别克隆入非分泌性真核表达载体ＶＲ１０１２和改建后的分泌型载体ＶＲ１０１２／ＴＡ中，通过ＰＣＲ和酶切鉴定出重组克隆。     

鼠约氏疟原虫yoelii株Pydyn基因的内含子序列分析

本研究测定并分析鼠约氏疟原虫 (Plasmodiumyoeliiyoelii)动力素蛋白基因 (Pydyn) 3′端内含子序列 ,比较约氏疟原虫yoelii虫株的Pydyn基因与约氏疟原虫 17XNL虫株基因组序列内含子间序列的多态性。方法 :应用PCR技术扩增约氏疟原虫动力素蛋白基因 (Pydyn)基因组 3′端序列 ,将其克隆入pGEM TEasy载体。阳性克隆经酶切和PCR鉴定正确后测序 ,并用分子生物学WINSTAR软件进行基因结构和同源性分析。结果 :用PCR方法成功扩增出约 80 0bp的Pydyn基因特定片段 ,阳性克隆经酶切及PCR扩增确定。基因序列分析表明 ,约氏疟原虫yoelii虫株的Pydyn基因含有 3个内含子 ,并且与约氏疟原虫 17XNL虫株基因组序列在内含子间存在着几个变异。结论 :确定了鼠约氏疟原虫动力素蛋白基因 (Pydyn) 3′端内含子序列 ,其内含子具有序列短且AT含量较高的特点 ,两末端的碱基具有一般真核基因内含子共有的剪接位点。多态性分析表明 ,将约氏疟原虫yoelii虫株的Pydyn基因的 3个内含子与人恶性疟原虫动力素基因Pfdyn内含子保守序列相比 ,Pydyn基因内含子上游下游序列具有一定的同源性。另外 ,约氏疟原虫yoelii虫株与约氏疟原虫 17XNL虫株的内含子间存在着多态性 ,存在着几个变异 ,这些变异属于点突变     

HIV1膜蛋白PND编码基因自然变异株的发现

目的 对1例来自华东地区HIV1分离株（WWBH7）的前病毒env基因C2-V3区进行序列分析。方法 以HIV1感染者外周血单个核细胞基因组为模板进行套式PCR扩增HIV1env基因C2-V3区片段,将此扩增产物插入T-Vector,酶切鉴定重组质粒,使用AB1737自动DNA序列测定仪测定序列并用DNASIS软件进行分析。结果 DNA序列资料显示该毒株属于HIV1B亚型衍生株,但与HIV1B亚型的标准株如SF2株相比,该HIV1毒株的env基因V3区下游有192bp的重复插入突变,使得该毒株的膜蛋白PND编码基因呈现双V3区的变异该段DNA序列已登录于GenBank(AF220245)。结论 该分离株是1个在膜蛋白PND编码基因有大片段插入突变的HIV1变异株。     

Antibodies to malaria vaccine candidates Pvs25 and Pvs28 completely block the ability of Plasmodium vivax to infect mosquitoes

Transmission-blocking vaccines are one strategy for controlling malaria, whereby sexual-stage parasites are inhibited from infecting mosquitoes by human antibodies. To evaluate whether the recently cloned Plasmodium vivax proteins Pvs25 and Pvs28 are candidates for a transmission-blocking vaccine, the molecules were expressed in yeast as secreted recombinant proteins. Mice vaccinated with these proteins adsorbed to aluminum hydroxide developed strong antibody responses against the immunogens, although for Pvs28, this response was genetically restricted. Antisera against both recombinant Pvs25 and Pvs28 recognized the corresponding molecules expressed by cultured sexual-stage parasites isolated from patients with P. vivax malaria. The development of malaria parasites in mosquitoes was completely inhibited when these antisera were ingested with the infected blood meal. Pvs25 and Pvs28, expressed in Saccharomyces cerevisiae, are as yet the only fully characterized transmission-blocking vaccine candidates against P. vivax that induce such a potent antiparasite response.     

Plasmodium vivax malaria vaccine development.

Plasmodium vivax represents the most widespread malaria parasite worldwide. Although it does not result in as high a mortality rate as P. falciparum, it inflicts debilitating morbidity and consequent economic impact in endemic communities. In addition, the relapsing behavior of this malaria parasite and the recent resistance to anti-malarials contribute to making its control more difficult. Although the biology of P. vivax is different from that of P. falciparum and the human immune response to this parasite species has been rather poorly studied, significant progress is being made to develop a P. vivax-specific vaccine based on the information and experience gained in the search for a P. falciparum vaccine. We have devoted great effort to antigenically characterize the P. vivax CS protein and to test its immunogenicity using the Aotus monkey model. Together with other groups we are also assessing the immunogenicity and protective efficacy of the asexual blood stage vaccine candidates MSP-1 and DBP in the monkey model, as well as the immunogenicity of Pvs25 and Pvs28 ookinete surface proteins. The transmission-blocking efficacy of the responses induced by these latter antigens is being assessed using Anopheles albimanus mosquitoes. The current status of these vaccine candidates and other antigens currently being studied is described.     

The surface protein Pvs25 of Plasmodium vivax ookinetes interacts with calreticulin on the midgut apical surface of the malaria vector Anopheles albimanus

Malaria parasite transmission-blocking control strategies within the mosquito vector require an adequate understanding of the parasite mosquito interaction at the molecular level. The ookinete P25-P28 surface proteins are required for the transition from ookinete to oocyst in the mosquito midgut; however, their respective molecular interactions in the mosquito are largely unknown. We used recombinant Pvs25 and Pvs28 as probes for identification of potential Anopheles albimanus midgut ligands. A 50 kDa protein interacted with Pvs25 but not with Pvs28 in blot overlay assays. This protein was identified as calreticulin by LS MS and was detected in membrane, but not in soluble midgut protein extracts. Calreticulin was detected in An. albimanus midgut microvilli by immunofluorescence analysis. The An. albimanus calreticulin cDNA was cloned and recombinant calreticulin was shown to interact with recombinant Pvs25 in overlay and co-immunoprecipitation assays, confirming the interaction of the two proteins. The Pvs25-calreticulin interaction in vivo could represent a potential target for developing transmission blocking strategies based on interfering the parasite-midgut interaction.     

Tricomponent immunopotentiating system as a novel molecular design strategy for malaria vaccine development

The creation of subunit vaccines to prevent malaria infection has been hampered by the intrinsically weak immunogenicity of the recombinant antigens. We have developed a novel strategy to increase immune responses by creating genetic fusion proteins to target specific antigen-presenting cells (APCs). The fusion complex was composed of three physically linked molecular entities: (i) a vaccine antigen, (ii) a multimeric α-helical coiled-coil core, and (iii) an APC-targeting ligand linked to the core via a flexible linker. The vaccine efficacy of the tricomponent complex was evaluated using an ookinete surface protein of Plasmodium vivax, Pvs25, and merozoite surface protein-1 of Plasmodium yoelii. Immunization of mice with the tricomponent complex induced a robust antibody response and conferred substantial levels of P. vivax transmission blockade as evaluated by a membrane feed assay, as well as protection from lethal P. yoelii infection. The observed effect was strongly dependent on the presence of all three components physically integrated as a fusion complex. This system, designated the tricomponent immunopotentiating system (TIPS), onto which any recombinant protein antigens or nonproteinaceous substances could be loaded, may be a promising strategy for devising subunit vaccines or adjuvants against various infectious diseases, including malaria.     

Blocking Effect of a Monoclonal Antibody against Recombinant Pvs25 on Sporozoite Development in Anopheles sinensis

To develop a vaccine to block the transmission of vivax malaria, the gene encoding the ookinete surface protein Pvs25 was cloned from a Korean malaria patient. The Pvs25 gene was 660 bp long, encoding 219 amino acids. It was subcloned into the expression vector pQE30 and expressed in Escherichia coli. The expressed recombinant protein, named rPvs25, showed a molecular mass of approximately 25 kDa by SDS-PAGE analysis. An anti-rPvs25 monoclonal antibody produced in BALB/c mice was able to inhibit sporozoite development in the mosquito Anopheles sinensis, which is known as the malaria transmission vector in the Republic of Korea. In addition, rPvs25 produced a relatively high antibody titer in BALB/c mice that lasted for more than 6 months. Based on these results, we suggest that recombinant Pvs25 could be a useful antigen in the development of a vaccine to prevent local malaria transmission in the Republic of Korea.Although Plasmodium vivax has presumably been prevalent in the Republic of Korea for several centuries, the incidence of vivax malaria has rapidly decreased as a result of a national malaria eradication program conducted by the Korean government in collaboration with the World Health Organization (WHO) (12, 13, 24). After a report of two malaria patients in 1985 (18), there were no further reported cases until 1993. Between 1993 and 2000, the number of malaria cases rapidly increased. Thus, starting in 2000, the Korean government made efforts to reduce the incidence of malaria, resulting in a decrease in reported malaria cases over the course of several years. Nevertheless, it is unlikely that malaria has been eradicated thoroughly from the Republic of Korea; treatment failure is reported for approximately 3 to 4% of cases every year (Korean Centers for Disease Control and Prevention, unpublished data), and there is a steady influx of travelers and workers from countries where malaria is prevalent. Malaria is caused by protozoan parasites of the genus Plasmodium, primarily Plasmodium falciparum and P. vivax, and is transmitted in nearly 100 countries, where approximately 2.0 billion people are exposed to infection. The WHO estimates that the global burden of malaria is approximately 500 million clinical cases per year, and recent estimates suggest that 70 to 80 million of those cases are due to P. vivax (24). Unfortunately, most trials for developing a malaria vaccine have not been successful because of the complicated life cycle of the malaria parasite. To overcome this problem, several researchers began to develop transmission-blocking vaccines (TBVs), which are designed to induce an immune response in the human host, inhibiting the formation of ookinetes or oocysts in the mosquito vector and thus preventing the spread of the parasites between humans. For example, in P. falciparum, monoclonal antibodies against the Pfs230 and Pfs48/45 proteins, which are expressed in the gametocytes/gametes, can block fertilization. In addition, monoclonal antibodies against the P25 and P21/28 surface protein family members, which are expressed in zygotes and ookinetes, can inhibit postfertilization events (2, 10). Proteins in the P25 and P21/28 families are distinctive, having four evolutionarily conserved tandem epidermal growth factor (EGF)-like domains attached to the parasite surface by a glycosylphosphatidylinositol (GPI) anchor. Pfs25 and Pfs28 of P. falciparum and Pfs28 of rodent malaria parasites have been cloned and are well characterized (5, 6, 20). In Plasmodium yoelii, antibodies against the P25 homolog Pys25 can inhibit zygote formation (22). In Plasmodium gallinacerum, polyclonal antibodies against Pgs28, the homolog of P21/28, inhibit the development of zygotes into ookinetes in vitro and the development of ookinetes into oocysts (4). In P. vivax, antibodies against Pvs25 and Pvs28, which were cloned from the SalI strain, have the ability to block parasite formation in infected mosquitoes (8). However, Pvs25 contains an antigenic polymorphism that causes problems with a SalI strain-based vaccine. Therefore, in this study, we report the cloning of the ookinete surface protein Pvs25 from a Korean isolate that could be a suitable antigen for the development of a transmission-blocking vaccine for use in South Korea. It would be time-consuming and laborious to immunize the more than 10 million individuals in areas of malaria endemicity in South Korea with precise immunization schedules. One way to circumvent the logistical difficulties would be to develop an edible malaria vaccine, so we also addressed whether immune responses could be evoked in vivo by the oral administration of the recombinant Pvs25 (rPvs25) protein.     

Baculovirus-Vectored Multistage Plasmodium vivax Vaccine Induces Both Protective and Transmission-Blocking Immunities against Transgenic Rodent Malaria Parasites

A multistage malaria vaccine targeting the pre-erythrocytic and sexual stages of Plasmodium could effectively protect individuals against infection from mosquito bites and provide transmission-blocking (TB) activity against the sexual stages of the parasite, respectively. This strategy could help prevent malaria infections in individuals and, on a larger scale, prevent malaria transmission in communities of endemicity. Here, we describe the development of a multistage Plasmodium vivax vaccine which simultaneously expresses P. vivax circumsporozoite protein (PvCSP) and P25 (Pvs25) protein of this species as a fusion protein, thereby acting as a pre-erythrocytic vaccine and a TB vaccine, respectively. A new-concept vaccine platform based on the baculovirus dual-expression system (BDES) was evaluated. The BDES-Pvs25-PvCSP vaccine displayed correct folding of the Pvs25-PvCSP fusion protein on the viral envelope and was highly expressed upon transduction of mammalian cells in vitro. This vaccine induced high levels of antibodies to Pvs25 and PvCSP and elicited protective (43%) and TB (82%) efficacies against transgenic P. berghei parasites expressing the corresponding P. vivax antigens in mice. Our data indicate that our BDES, which functions as both a subunit and DNA vaccine, can offer a promising multistage vaccine capable of delivering a potent antimalarial pre-erythrocytic and TB response via a single immunization regimen.     

Plasmodium vivax malaria in the Brazilian Amazon: some aspects of its epidemiology, clinical spectrum and naturally induced immune responses

Malaria was a nationwide problem in Brazil in the 1940's. However during the late fifties a national and successful campaign gained strength in the country decreasing malaria to its lowest level by 1960, when only 36,9 thousand cases were registered. Although the Malaria Eradication Program of the Ministry of Health in Brazil succeeded by the late 60's in freeing the majority of the country from malaria transmission, it was unable to contain the rapid spread of the disease in the Amazon Basin. In the 1970's the Amazon region witnessed a huge transformation. Colonization programs sponsored by the government, mining exploration, massive migration and the construction of roads and dams brought a new reality for which the area was not prepared. The last data available show that in 2007, the Amazon registered around 450 thousand cases, 99.9% of the national cases. P. vivax has been reported as representing around 80% of all malaria cases. P. vivax is thought to cause little mortality but like P. falciparum, P. vivax accounts for vast amounts of morbidity and for huge burdens on the prosperity of endemic communities. However, in the last few years a pattern of unusual clinical complications with fatal cases associated with it have been reported in Brazil and is a matter of tremendous concern in the Brazilian community of malariologists. In addition, the emergence of P. vivax strains resistant to chloroquine and primaquine in some reports needs to be further investigated. In contrast, asymptomatic infections by P. falciparum and P. vivax were detected in epidemiological studies in the states of Rondonia and Amazonas. Seropidemiological studies investigating the type of immune responses elicited in naturally exposed populations to several malaria vaccine candidates in Brazilian populations have also been providing important information on whether immune responses specific to those antigens are generated in natural infections and their immunogenic potential as vaccine candidates. In fact ultimate test of a malaria vaccine will be determined in field trials under natural conditions of parasite exposure.     

Recent independent evolution of msp1 polymorphism in Plasmodium vivax and related simian malaria parasites

The Plasmodium MSP-1 is a promising malaria vaccine candidate. However, the highly polymorphic nature of the MSP-1 gene (msp1) presents a potential obstacle for effective vaccine development. To investigate the evolutionary history of msp1 polymorphism in P. vivax, we construct phylogenetic trees of msp1 from P. vivax and related monkey malaria parasite species. All P. vivax msp1 alleles cluster in the P. vivax lineage and are not distributed among other species. Similarly, all P. cynomolgi msp1 alleles cluster in the P. cynomolgi lineage. This suggests that, in contrast to presumed ancient origin of P. falciparum msp1 polymorphism, the origin of P. vivax msp1 polymorphism is relatively recent. We observed positive selection in the P. vivax lineage but not in P. cynomolgi. Also, positive selection acts on different regions of msp1 in P. vivax and P. falciparum. This study shows that the evolutionary history of msp1 differs greatly among parasite lineages.     

Evaluation of the safety and immunogenicity in rhesus monkeys of a recombinant malaria vaccine for Plasmodium vivax with a synthetic Toll-like receptor 4 agonist formulated in an emulsion

Plasmodium vivax is the major cause of malaria outside sub-Saharan Africa and inflicts debilitating morbidity and consequent economic impacts in developing countries. In order to produce a P. vivax vaccine for global use, we have previously reported the development of a novel chimeric recombinant protein, VMP001, based on the circumsporozoite protein (CSP) of P. vivax. Very few adjuvant formulations are currently available for human use. Our interest is to evaluate second-generation vaccine formulations to identify novel combinations of adjuvants capable of inducing strong, long-lasting immune responses. In this study rhesus monkeys were immunized intramuscularly three times with VMP001 in combination with a stable emulsion (SE) or a synthetic Toll-like receptor 4 (TLR4) agonist (glucopyranosyl lipid A [GLA]) in SE (GLA-SE). Sera and peripheral blood mononuclear cells (PBMCs) were tested for the presence of antigen-specific humoral and cellular responses, respectively. All groups of monkeys generated high titers of anti-P. vivax IgG antibodies, as detected by enzyme-linked immunosorbent assays (ELISAs) and immunofluorescence assays. In addition, all groups generated a cellular immune response characterized by antigen-specific CD4(+) T cells secreting predominantly interleukin-2 (IL-2) and lesser amounts of tumor necrosis factor (TNF). We conclude that the combination of VMP001 and GLA-SE is safe and immunogenic in monkeys and may serve as a potential second-generation vaccine candidate against P. vivax malaria.     

Fine specificity of Plasmodium vivax Duffy binding protein binding engagement of the Duffy antigen on human erythrocytes

Plasmodium vivax invasion of human erythrocytes requires interaction of the P. vivax Duffy binding protein (PvDBP) with its host receptor, the Duffy antigen (Fy) on the erythrocyte surface. Consequently, PvDBP is a leading vaccine candidate. The binding domain of PvDBP lies in a cysteine-rich portion of the molecule called region II (PvDBPII). PvDBPII contains three distinct subdomains based upon intramolecular disulfide bonding patterns. Subdomain 2 (SD2) is highly polymorphic and is thought to contain many key residues for binding to Fy, while SD1 and SD3 are comparatively conserved and their role in Fy binding is not well understood. To examine the relative contributions of the different subdomains to binding to Fy and their abilities to elicit strain-transcending binding-inhibitory antibodies, we evaluated recombinant proteins from SD1+2, SD2, SD3, and SD3+, which includes 24 residues of SD2. All of the recombinant subdomains, except for SD2, bound variably to human erythrocytes, with constructs containing SD3 showing the best binding. Antisera raised in laboratory animals against SD3, SD3+, and SD2+3 inhibited the binding of full-length PvDBPII, which is strain transcending, whereas antisera generated to SD1+2 and SD2 failed to generate blocking antibodies. All of the murine monoclonal antibodies generated to full-length PvDBPII that had significant binding-inhibitory activity recognized only SD3. Thus, SD3 binds Fy and elicits blocking antibodies, indicating that it contains residues critical to Fy binding that could be the basis of a strain-transcending candidate vaccine against P. vivax.