Chronic congestive heart failure. Description and survival of 190 consecutive patients with a diagnosis of chronic congestive heart failure based on clinical signs and symptoms

The malaria parasite life cycle presents several targets for attack, but these different parts of the life cycle are susceptible to different types of host immune response. For example, the sporozoite is most sensitive to immune antibody, while liver stage parasites can be eliminated by cytotoxic T lymphocytes. Attachment of merozoites to erythrocytes, on the other hand, can be blocked by antibody. Convincing experimental evidence shows that completely protective immunity to malaria can be induced. The challenge now is to design recombinant or synthetic vaccines that induce the right types of immune responses to specific life cycle stages. This requires the identification and characterization of B- and T-lymphocyte epitopes expressed by the parasite or by parasitized host cells. These epitopes must be incorporated into a delivery system that maximizes the interaction between the vaccine epitopes and the host immune system. Many epitopes from several parts of the life cycle are already characterized; development of multivalent vaccines, that is, vaccines which contain immunogens from more than one part of the life cycle, is a promising area for research efforts.     

A novel Plasmodium falciparum sporozoite and liver stage antigen (SALSA) defines major B, T helper, and CTL epitopes

In the search for subunit vaccines that are able to induce the type of sterile, protective immunity achieved by irradiated sporozoites, there is increasing evidence that defense mechanisms directed at the intrahepatic stage and Ags expressed at this stage are critical. We have initiated a systematic search for such molecules and report here the identification and partial characterization of a novel Plasmodium falciparum gene encoding a 70-kDa protein, expressed in both sporozoite and liver stages (SALSA), with a vaccine potential that stems from its antigenic features. Antigenicity and immunogenicity studies were conducted in individuals exposed to malaria, in immunized mice, and in chimpanzees, using a recombinant protein and two synthetic peptides. Results show that the SALSA nonrepetitive sequence defines 1) major B cell epitopes, as shown by a high prevalence of Abs to each peptide in three African areas differing in their level of endemicity; 2) Th epitopes, as demonstrated by lymphoproliferation and IFN-gamma secretion in cells from the individuals from one of the low transmission areas, as well as helper effect upon Ab secretion in mice; and 3) epitopes for cytolytic lymphocytes, demonstrated in immunized and sporozoite-challenged chimpanzees, and associated with MHC class I leukocyte Ags. The latter are of particular importance, because this is the only part of the malaria life cycle in which the parasite is located in a cell expressing class I Ags and because CD8+ lymphocytes were found to be responsible for protection in experimental models.     

Malaria vaccine: roadblocks and possible solutions

Malaria remains the most prevalent and devastating parasitic disease worldwide. Vaccination is considered to be an approach that will complement other strategies for prevention and control of the disease in the future. In the last 10 years, intense studies aimed at the development of a malaria vaccine have provided important knowledge of the nature of the host immunological mechanisms of protection and their respective target antigens. It became well established that protective immune responses can be generated against the distinct stages of Plasmodium. However, in general, protective immune responses are directed at stage-specific antigens. The elucidation of the primary structure of these antigens made possible the generation of synthetic and recombinant proteins that are being extensively used in experimental immunizations against the infection. Today, several epitopes of limited polymorphism have been described and protective immunity can be generated by immunization with them. These epitopes are being tested as primary candidates for a subunit vaccine against malaria. Here we critically review the major roadblocks for the development of a malaria vaccine and provide some insight on how these problems are being solved.     

Antigenicity and immunogenicity of multiple antigen peptides (MAP) containing P. vivax CS epitopes in Aotus monkeys

Using linear synthetic peptides corresponding to the Plasmodium vivax circumsporozoite (CS) protein of the common type, we have identified several T and B-cell epitopes recognized by human individuals. Three T-cell epitopes studied (p6) from the amino, (p11) from the central and (p25) from the carboxyl regions, were widely recognized by lymphocytes of immune donors. A series of six peptides, in addition to p11, representing the central repeat domain of the CS(p11-p17) protein were used in ELISA assays to map the B-cell epitopes of this region. P11 was the peptide most frequently recognized by sera containing antibodies to the homologous CS protein as determined by IFAT. The sequences corresponding to peptides p6, p11 and P25 as well as that representing a universal T-cell epitope derived from the tetanus toxin were used to assemble eight different Multiple Antigen Peptides (MAP). The immunogenicity of these MAP was analysed in Aotus monkeys. Groups of two animals were immunized with each MAP and both antibody response, T-lymphocyte proliferation and in vitro gamma-IFN production were evaluated. Two MAPs containing the same B-cell epitope and either a promiscuous CS-protein derived T-cell epitope (p25) or the tetanus toxin epitope (p-tt30) proved to be the most immunogenic and induced high levels of anti-peptide antibodies that recognized the native protein. Except for animals immunized with MAP VII, there was no correlation between antibody levels, lymphocyte proliferation or gamma-IFN production in vitro. The broad recognition of these epitopes by individuals which had been exposed to malaria, the capacity of these MAPs to induce antibodies, recognize the cognate protein, and in vitro gamma-IFN production encourages further analyses of the potential of these proteins as malaria vaccine candidates for human use.     

Protection against malaria by immunization with plasmid DNA encoding circumsporozoite protein

Immunization with irradiated sporozoites protects animals and humans against malaria, and the circumsporozoite protein is a target of this protective immunity. We now report that adjuvant-free intramuscular injection of mice with plasmid DNA encoding the Plasmodium yoelii circumsporozoite protein induced higher levels of antibodies and cytotoxic T lymphocytes against the P. yoelii circumsporozoite protein than did immunization with irradiated sporozoites. Mice immunized with this vaccine had an 86% reduction in liver-stage parasite burden after challenge with 5 x 10(5) sporozoites (> 10(5) median infectious doses). Eighteen (68%) of 28 mice that received two or three doses of vaccine were protected against challenge with 10(2) sporozoites, and the protection was dependent on CD8+ T cells. These studies demonstrate the utility of plasmid DNA immunization against a nonviral infection. By obviating the requirement for peptide synthesis, expression and purification of recombinant proteins, and adjuvants, this method of immunization provides an important alternative for rapid identification of protective B- and T-cell epitopes and for construction of vaccines to prevent malaria and other infectious diseases.     

Development of a malaria vaccine

Development of an effective malaria vaccine poses a major scientific challenge both in the laboratory and in the field. Such a vaccine is necessary because of the massive disease burden of malaria in the developing world, the global spread of drug resistance, and the difficulty of sustainable control of the mosquito vector. Animal models have shown the immunological feasibility of vaccines targeted against different stages of parasite development, and studies in human volunteers have shown that a recombinant protein vaccine can protect against challenge with the homologous strain of parasite. However, both natural and vaccine-induced immunity are hampered by the remarkable capacity of the parasites to vary critical antigenic structures; large field trials of a synthetic peptide vaccine gave equivocal results. In an attempt to overcome the dual difficulty of poor immunogenicity and parasite diversity, much experimental work is now focused on complex antigenic constructs, delivered as DNA vaccines or in live vectors such as vaccinia, with multiple targets at each stage of parasite development.     

Identification of a subpopulation of immune Nigerian adult volunteers by antibodies to the circumsporozoite protein of Plasmodium falciparum

Collections of human sera from malaria-endemic areas would be valuable for identifying and characterizing antigens as malaria vaccine candidates if the contributing serum donors' ability to resist infection were fully characterized. We prepared such a serum collection from 26 apparently immune Nigerian adults who failed to develop patent parasitemia for at least 20 weeks following a documented increase in antibodies to the circumsporozoite protein (CSP) from Plasmodium falciparum. Volunteers were evaluated five times per week for malaria symptoms and bimonthly for parasites by examining thick blood smears. The incidence rate over 13 months for the cohort was 42% (47 malaria-confirmed volunteers) and the risk of infection was 1.3 infections/year. Responses to CSP did not correlate with protection. Because antibody responses to antigens other than CSP may be associated with protection, the sera from these immune individuals may be useful for identifying and characterizing other potential malaria vaccine candidates.     

Pseudomonas aeruginosa antigens as potential vaccines

Pseudomonas aeruginosa is one of the most important opportunistic bacterial pathogens in humans and animals. This organism is ubiquitous and has high intrinsic resistance to antibiotics due to the low permeability of the outer membrane and the presence of numerous multiple drug efflux pumps. Various cell-associated and secreted antigens of P. aeruginosa have been the subject of vaccine development. Among pseudomonas antigens, the mucoid substance, which is an extracellular slime consisting predominantly of alginate, was found to be heterogenous in terms of size and immunogenicity. High molecular mass alginate components (30-300 kDa) appear to contain conserved epitopes while lower molecular mass alginate components (10-30 kDa) possess conserved epitopes in addition to unique epitopes. Surface-exposed antigens including O-antigens (O-specific polysaccharide of LPS) or H-antigens (flagellar antigens) have been used for serotyping due to their highly immunogenic nature. Chemical structures of repeating units of O-specific polysaccharides have been elucidated and these data allowed the identification of 31 chemotypes of P. aeruginosa. Conserved epitopes among all serotypes of P. aeruginosa are located in the core oligosaccharide and the lipid A region of LPS and immunogens containing these epitopes induce cross-protective immunity in mice against different P. aeruginosa immunotypes. To examine the protective properties of OM proteins, a vaccine containing P. aeruginosa OM proteins of molecular masses ranging from 20 to 100 kDa has been used in pre-clinical and clinical trials. This vaccine was efficacious in animal models against P. aeruginosa challenge and induced high levels of specific antibodies in human volunteers. Plasma from human volunteers containing anti-P. aeruginosa antibodies provided passive protection and helped the recovery of 87% of patients with severe forms of P. aeruginosa infection. Vaccines prepared from P. aeruginosa ribosomes induced protective immunity in mice, but the efficacy of ribosomal vaccines in humans is not yet known. A number of recent studies indicated the potential of some P. aeruginosa antigens that deserve attention as new vaccine candidates. The outer core of LPS was implicated to be a ligand for binding of P. aeruginosa to airway and ocular epithelial cells of animals. However, heterogeneity exists in this outer core region among different serotypes. Epitopes in the inner core are highly conserved and it has been demonstrated to be surface-accessible, and not masked by O-specific polysaccharide. The use of an in vivo selection/expression technology (IVET) by a group of researchers identified a number of P. aeruginosa proteins that are expressed in vivo and essential for virulence. Two of these in vivo-expressed proteins are FptA (ferripyochelin receptor protein) and a homologue of an LPS biosynthetic enzyme. Our laboratory has identified a highly conserved protein, WbpM, and P. aeruginosa with a deficiency in this protein produces only rough LPS and became serum sensitive. Results from these studies have provided the foundation for a variety of vaccine formulations.     

Mapping of specific and promiscuous HLA-DR-restricted T-cell epitopes on the Plasmodium falciparum 27-kilodalton sexual stage-specific antigen

We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual stage-specific antigen, of the human malaria parasite Plasmodium falciparum in subjects with a history of malaria. Pfg27, expressed early in the sexual stages, is recognized by monoclonal antibodies capable of reducing the infectivity of gametocytes in mosquitoes. By using 16 Pfg27-specific CD4(+)-T-cell clones derived from three donors, seven different T-cell epitopes were identified. Among them, P11 (amino acids 191 to 210 of the Pfg27 sequence, IDVVDSYIIKPIPALPVTPD) was found to contain a previously described binding motif for multiple HLA-DR allotypes. Indeed, P11 was found to be promiscuous in that it could be recognized by T cells in the context of at least five different HLA-DR molecules. The cytokine profile of the clones was mixed. Seven of nine T-cell clones exhibited a Th0-like cytokine profile, producing high levels of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) upon stimulation with specific peptides and mitogens. The other two clones had a Th1-like cytokine profile with high expression of IFN-gamma and no IL-4. Identification of a promiscuous epitope in Pfg27 could play a significant role in the design of a subunit vaccine for suppressing malaria transmission.     

Vaccination against malaria. Disappointments and hopes

After the first in vitro cultivation of Plasmodium falciparum 21 years ago, the prospect of anti-malarial vaccination arose many hopes, but, in the end, it so far has mainly given rise to doubts and disappointments. Technically, the problem is particularly difficult. Plasmodium falciparum has a very complex antigenic structure with several hundreds, if not several thousands, of different epitopes for each of the four main evolutive stages of the parasite (sporozoites, merozoites, gametocytes, ookinetes) which correspond to different phase of the infection and could be a target for vaccination. Many of these epitopes are stage-specific and some of them vary from one strain to another. Adjuvants also play a major role and can qualitatively modify the type of immune response. The immune mechanisms also differ according to the final goal: anti-Plasmodium infection or anti-disease vaccine. Over the last few years, the first clinical assays have been carried out with the Spf66 vaccine, a synthetic complex protein directed against sporozoites and merozoites. In adults and children, the first results in South America and in East Africa were modest but encouraging. Unfortunately they were not confirmed by further studies in West Africa and South-East Asia. Two new types of vaccines are under preliminary clinical evaluation. One is directed against ookinetes of Plasmodium falciparum (Pfs25 and Pfs28) and can stop the transmission from the mosquito. The other is an anti-sporozoite vaccine with a new immunogen (RTS,S) in which the circumsporozoite protein is fused to the hepatitis B surface antigen and can protect against infestation. New prospects and improvements are offered by the technique of DNA vaccines and will probably also result from better knowledge of cellular and molecular biology of the parasite which is being extensively studied (genomic structure). If new promising perspectives exist, it is particularly important to be careful to avoid such disappointments as those caused, in the past, by a too-optimistic and over-publicized presentation of some preliminary results. It is now certain that one or several malaria-vaccines will be available, but no one can seriously say when, for whom and how. In any case, it is unrealistic to hope that vaccine(s) alone will be able to eradicate such an epidemiologically complex disease as malaria. It is probable that only the coordinated use of all the techniques available (anti-vectorial protection and fight, chemoprophylaxis and chemotherapy, vaccination) will lead to success.     

Short report: identification of B-cell epitopes in the serine-rich Entamoeba histolytica protein

The serine-rich Entamoeba histolytica protein (SREHP) has been shown to be a protective antigen in animal models of amebic liver abscess when delivered by either parenteral or oral routes of immunization, and antibodies to SREHP can prevent amebic liver abscess in severe combined immunodeficient mice. To identify B cell epitopes of the SREHP molecule that could serve as the basis for a peptide-based vaccine, we synthesized overlapping peptides spanning the amino acid sequence of SREHP, and looked at the reactivity of serum samples from five individuals with amebic liver abscess to the overlapping peptides. We found that most of the epitopes recognized by serum samples from patients with amebic liver abscess map to the hydrophilic dodecapeptide or octapeptide repeats of SREHP, but there was no universal epitope recognized by all five serum samples. In addition, we show that synthetic peptides that include the epitopes of SREHP recognized in the mapping study are immunogenic in animals and can generate antibodies that recognize SREHP.     

Dominance of conserved B-cell epitopes of the Plasmodium falciparum merozoite surface protein, MSP1, in blood-stage infections of naive Aotus monkeys

We have shown that conserved B epitopes were immunodominant in animals hyperimmunized with parasite-purified or recombinant merozoite surface protein MSP1 of Plasmodium falciparum. Cross-priming studies also suggested that a conserved T-helper epitope(s) is efficient in inducing the anti-MSP1 antibody response. In this study, we determined whether a similar profile of immune responses was induced during live P. falciparum infections. Naive Aotus monkeys were infected by blood-stage challenge with either one of the two dimorphic MSP1 alleles represented by the FUP and FVO parasites. Sera collected after parasite clearance were analyzed by enzyme-linked immunosorbent assays (ELISAs). Monkeys infected with parasites carrying one allelic form of MSP1 had antibodies that were equally reactive with homologous or heterologous MSP1s. This preferential recognition of conserved epitopes of MSP1 was confirmed by competitive binding ELISAs. Studies with Plasmodium yoelii and P. falciparum show that the C-terminal 19-kDa fragment of MSP1, MSP1(19), is the target of protective immunity. Thus, monkey sera were assayed for recognition with recombinant MSP1(19)s expressing variant and conserved B epitopes. Results of direct and competitive binding ELISAs showed that the anti-MSP1(19) antibodies were also directed primarily against conserved determinants. The similarities between vaccine- or infection-induced antibody responses suggest a possible reciprocal enhancement of the two populations of anti-MSP1 antibodies when a subunit MSP1 vaccine is introduced into populations living in areas where malaria is endemic. This together with previous observations that conserved determinants are important in MSP1-mediated immunity provides an optimistic outlook that a subunit MSP1 vaccine may be effective and practical for field applications in malaria-exposed populations.     

Immunization of Aotus nancymai with recombinant C terminus of Plasmodium falciparum merozoite surface protein 1 in liposomes and alum adjuvant does not induce protection against a challenge infection

Merozoite surface protein 1 (MSP-1) of Plasmodium falciparum is an antimalarial vaccine candidate. The highly conserved 19-kDa C-terminal processing fragment of MSP-1 (MSP-1(19)) is of particular interest since it contains epitopes recognized by monoclonal antibodies which inhibit the invasion of erythrocytes in vitro. The presence of naturally acquired anti-MSP-1(19) antibodies in individuals exposed to malaria has been correlated with reduced morbidity, and immunization with an equivalent recombinant P. yoelii antigen induces substantial protection against this parasite in mice. We have expressed P. falciparum MSP-1(19) in Escherichia coli as a correctly folded protein and immunized Aotus nancymai monkeys by using the protein incorporated into liposomes and adsorbed to alum. After vaccination, the sera from these animals contained anti-MSP-1(19) antibodies, some of which competed for binding to MSP-1(19) with monoclonal antibodies that inhibit parasite invasion of erythrocytes in vitro. However, after challenge with either a homologous or a heterologous strain of parasite, all animals became parasitemic and required treatment. The immunization did not induce protection in this animal model.     

Antibodies that inhibit malaria merozoite surface protein-1 processing and erythrocyte invasion are blocked by naturally acquired human antibodies

Merozoite surface protein-1 (MSP-1) of the human malaria parasite Plasmodium falciparum undergoes at least two endoproteolytic cleavage events during merozoite maturation and release, and erythrocyte invasion. We have previously demonstrated that mAbs which inhibit erythrocyte invasion and are specific for epitopes within a membrane-proximal, COOH-terminal domain of MSP-1 (MSP-119) prevent the critical secondary processing step which occurs on the surface of the extracellular merozoite at around the time of erythrocyte invasion. Certain other anti-MSP-119 mAbs, which themselves inhibit neither erythrocyte invasion nor MSP-1 secondary processing, block the processing-inhibitory activity of the first group of antibodies and are termed blocking antibodies. We have now directly quantitated antibody-mediated inhibition of MSP-1 secondary processing and invasion, and the effects on this of blocking antibodies. We show that blocking antibodies function by competing with the binding of processing-inhibitory antibodies to their epitopes on the merozoite. Polyclonal rabbit antibodies specific for certain MSP-1 sequences outside of MSP-119 also act as blocking antibodies. Most significantly, affinity-purified, naturally acquired human antibodies specific for epitopes within the NH2-terminal 83-kD domain of MSP-1 very effectively block the processing-inhibitory activity of the anti-MSP-119 mAb 12.8. The presence of these blocking antibodies also completely abrogates the inhibitory effect of mAb 12.8 on erythrocyte invasion by the parasite in vitro. Blocking antibodies therefore (a) are part of the human response to malarial infection; (b) can be induced by MSP-1 structures unrelated to the MSP-119 target of processing-inhibitory antibodies; and (c) have the potential to abolish protection mediated by anti-MSP-119 antibodies. Our results suggest that an effective MSP-119-based falciparum malaria vaccine should aim to induce an antibody response that prevents MSP-1 processing on the merozoite surface.     

Identification of epitopes on a mutant form of Pseudomonas exotoxin using serum from humans treated with Pseudomonas exotoxin containing immunotoxins

PE38 is a 38-kDa derivative of the 66-kDa Pseudomonas exotoxin (PE) in which the cell binding domain of PE (domain Ia, amino acids 1-252) and a portion of domain Ib (amino acids 365-380) are deleted. The immunotoxins LMB-1 and LMB-7 contain PE38 and kill cancer cells by exploiting the cytotoxic action of PE38. The major human B cell epitopes of PE38 were mapped by measuring the reactivity of 45 serum samples from patients treated with the PE38-containing immunotoxins LMB-1 or LMB-7 to two panels of overlapping synthetic peptides representing the sequence of PE38. One panel of peptides is ten amino acids long and overlap by seven amino acids, and the second panel of peptides is twenty amino acids long and overlap by ten. Five major epitopes were identified: amino acids 274-283, 470-492, 531-540, 555-564, and the C-terminal amino acids 596-609. Two minor epitopes were identified as well: amino acids 501-510 and 582-589. These epitopes are predominantly located on the surface of the protein. The amino acids believed to be critical for binding are highly solvent-accessible residues. The results of the human antibody response to peptides are compared to the pattern of reactivity previously identified with serum samples obtained from monkeys administered LMB-1 and LMB-7. The epitopes between monkey and human are almost identical, demonstrating similarity in the response of antibody repertoires between the two species and providing further support that these are the immunodominant epitopes. This information is critical for genetically engineering less immunogenic immunotoxins and provides a foundation for the development of a vaccine against pseudomonal infections which plague immunocompromised individuals and individuals with cystic fibrosis.     

Percutaneous endovascular stent-graft repair of iliac artery aneurysms

There has been a tremendous explosion in the area of DNA vaccine research over the last 4 years, particularly in relation to antiviral vaccines. This report discusses the development and application of this new technology with regard to parasitic infections. Progress has been made towards the development of a vaccine against malaria, cryptosporidiosis, leishmaniasis, toxoplasmosis and schistosomiasis. In the future, nucleic acid vaccines will be a useful tool to help control these and other parasitic infections.     

T-cell immunity to peptide epitopes of liver-stage antigen 1 in an area of Papua New Guinea in which malaria is holoendemic

Liver-stage antigen 1 (LSA1) is one of several pre-erythrocytic antigens considered for inclusion in a multiantigen, multistage subunit vaccine against falciparum malaria. We examined T-cell proliferation and cytokine responses to peptides corresponding to amino acids 84 to 107, 1813 to 1835, and 1888 to 1909 of LSA1 in asymptomatic adults living in an area of Papua New Guinea where malaria is holoendemic. Whereas T cells from North Americans never exposed to malaria did not respond to any of the peptides, those from 52 of 55 adults from the area where malaria is endemic had vigorous proliferation responses to one or more of the LSA1 peptides (mean stimulation indices of 6.8 to 7.2). Gamma interferon (IFN-gamma) production driven by LSA1 peptides ranged from 34 to more than 3,500 pg/2 x 10(6) cells, was derived primarily from CD8+ cells, and was dissociated from T-cell proliferation. The frequencies of IFN-gamma response to the amino acid 1819 to 1835 and 1888 to 1909 peptides were significantly greater than that to the amino acid 84 to 107 peptide (87 and 88% versus 33% of subjects; P < 0.0001). In contrast to proliferation and IFN-gamma, interleukin 4 (IL-4) and/or IL-5 responses to LSA1 peptides were detected in only 18% of the subjects. These data show that T-cell immunity to epitopes in the N- and C-terminal regions of LSA1 are common in persons living in this area of Papua New Guinea where malaria is endemic. The dominance of type 1 CD8 cell IFN-gamma responses is consistent with a role for this T-cell population in immunity to liver-stage Plasmodium falciparum in humans.     

Reduced amide pseudopeptide analogues of a malaria peptide possess secondary structural elements responsible for induction of functional antibodies which react with native proteins expressed in Plasmodium falciparum erythrocyte stages

A psi[CH2NH] isoster bond was introduced by replacing one peptide bond at a time within the 1513 malaria peptide KEKMV motif to obtain a set of five pseudopeptides. The motif belongs to a Plasmodium falciparum malarial peptide coded 1513, derived from the MSP-1 protein. This high-binding motif included in the 1513 peptide is involved in the attachment of the malarial parasite to human erythrocytes. The novel malaria 1513 psi[CH2NH] surrogates were analyzed using RP-HPLC and MALDI-TOF mass spectrometry techniques. Nuclear magnetic resonance experiments allowed definition of the five pseudopeptide analogues' secondary structural features. Such structures are present in only a very few molecules in the 1513 parent peptide. A molecular model demonstrating the solution of the three-dimensional structure of the 1 513 peptide Pse-437 analogue was constructed on the basis of 1H-NMR spectral parameters. Monoclonal antibodies were generated to the five 1513 malaria peptide pseudopeptide analogues. These antibodies not only recognize the native MSP-1 (195 kDa) and its 83 kDa and 42 kDa proteolytic processing proteins but also different SPf(66)n malaria vaccine batches containing the native sequence. In addition, the mAbs were able to modify the kinetics of Plasmodium falciparum parasites' intraerythrocytic development and their ability to invade new RBCs. The presented evidence suggests that peptide bond-modified peptides could reproduce a transient state in 1513's native sequence and represent useful candidates in the development of a second generation of effective malarial vaccines.     

Plasmodium vivax: epitope mapping of monoclonal antibodies against the N-terminal region of the merozoite surface protein 1

Plasmodium vivax is the most widely distributed human malaria with an estimate of 35 million cases per year. The deduced amino acid sequence comparisons of the Merozoite Surface Protein 1 (MSP1) from several plasmodial species, including that of P. vivax (PvMSP1), revealed the existence of highly conserved blocks and polymorphic blocks. We had previously shown that sequences within conserved blocks from the N-terminal region of the PvMSP1 were poorly immunogenic in natural human infections. These results suggest that these regions code for important and unknown structural and/or functional features and thus they could potentially be tested as a sub-unit PvMSP1 vaccine. In the present study, a battery of monoclonal antibodies (Mabs) was produced against the N-terminal region of the PvMSP1 in an attempt to determine whether these N-terminal ICBs contained all the epitopes exposed on the native molecule. The results suggest that the most terminal ICB2 and ICB3 blocks are not exposed on the surface of the PvMSP1 native molecule and clearly eliminate the possibility of considering the N-terminal domains as unique components of a sub-unit PvMSP1 vaccine candidate.