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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The detection of pathogens by polymerase chain reaction (PCR) in clinical samples, such as blood, urine, or feces, requires initial sample preparation to remove polymerase inhibitors and to concentrate the target DNA. Here we show for the first time that immunomagnetic separation can be used to recover pathogens from whole blood and then used for PCR analysis. With antibodies to the merozoite surface protein (MSP1), the malaria-causing parasite Plasmodium falciparum was purified and concentrated from clinical samples. The recovered parasites were used directly for in vitro DNA amplification. The PCR product was subsequently analyzed by a colorimetric 96-well microtiter plate assay. The results from examining 117 patients attending a clinic in the Borai district, Thailand, demonstrate that the combined method with immunomagnetic separation followed by PCR increases the group of positively diagnosed patients compared with microscopic examination of stained blood films. Analysis of 1 microliter of whole blood resulted in a 12% (14 of 117) increase in positively diagnosed patients while a 10-microliters sample volume increased the positives diagnosed to 20.5% (24 of 117).
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PMID:Immunomagnetic purification to facilitate DNA diagnosis of Plasmodium falciparum. 825 71

Two clones of the human malaria parasite Plasmodium falciparum, denoted 3D7 and HB3, were grown in vitro under conditions permitting the development of gametocytes. The two clones differ in their allelic forms of two antigen genes MSP1 and MSP2. The alleles can be distinguished as size differences of polymerase chain reaction (PCR) amplified fragments of repetitive regions of each gene. Mosquitoes (Anopheles stephensi) were fed on a mixture of these gametocytes. A total of 128 oocysts was isolated from the midguts of infected mosquitoes from 9 crossing experiments between the clones. DNA extracted from these oocysts was amplified by PCR. Oocysts which contained both alleles of each gene (MSP1 and MSP2) had developed from heterozygotes produced by cross-fertilization events between 3D7 and HB3 gametes. The remaining oocysts contained single alleles of each gene, in parent clone combinations, and these had developed from homozygotes formed by self-fertilizations. The results suggest that gametes in the original mixture fed to mosquitoes had undergone random mating.
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PMID:Frequency of cross-fertilization in the human malaria parasite Plasmodium falciparum. 835 94

The merozoite surface protein MSP1, which is one of the most promising candidates for a malaria vaccine directed against erythrocytic stages, has been shown to be polymorphic in different malarial species. Characterization of the Plasmodium vivax MSP1 gene (Pv200) in two strains (Belem and Salvador-1) revealed the existence of several polymorphic regions. One of these regions has been examined here in primary parasite isolates obtained from patients in Sri Lanka. Oligonucleotide primers hybridizing to conserved parts of the gene on either side of a polymorphic region were used to amplify DNA from 22 isolates. Sequence analysis of the amplified portion of the MSP1 gene in five patients showed the existence of three types of polymorphic regions. Two were almost identical either to that of the Belem or to that of the Salvador-1 strain. The third polymorphic type appeared to have resulted from recombination between the two others. This recombination event took place inside a repeated part of the sequence.
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PMID:Plasmodium vivax:recombination between potential allelic types of the merozoite surface protein MSP1 in parasites isolated from patients. 845 28

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.
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PMID:Dominance of conserved B-cell epitopes of the Plasmodium falciparum merozoite surface protein, MSP1, in blood-stage infections of naive Aotus monkeys. 861 53

Malaria infection induces the production of serum antibodies to a variety of malaria antigens but the prevalence of antibodies to any particular antigen is typically much less than 100%. It has been assumed that non-responsiveness to defined antigens in malaria immune subjects is due to HLS-mediated restriction of the immune response. In this study we have investigated the role of HLA and non-HLA genes in the antibody response to two merozoite surface antigens (MSP1 and MSP2) and a sexual stage antigen (Ps260/230) of Plasmodium falciparum, and conclude that host genotype is not a major determinant of responsiveness. Although antibody levels vary in accordance with seasonal variations in malaria transmission in semi-immune children, antibody levels remain stable in clinically immune adults. Antigen recognition is selective with individual donors showing consistent high titre responses to some antigens/epitopes whilst consistently failing to recognize adjacent regions/epitopes of the same protein. An alternative explanation, consistent with the data presented here, is that selective antibody responses to malaria antigens in immune individuals result from a process akin to clonal imprinting (original antigenic sin).
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PMID:Selective recognition of malaria antigens by human serum antibodies is not genetically determined but demonstrates some features of clonal imprinting. 867 80

This paper considers methods of statistical analysis for highly skewed immune response data. Observations from population studies of immunological variables are rarely normally distributed between individuals; typically the distribution shows extreme levels of skewness. In some situations, skewness remains considerable even after transforming the data. Using resampling techniques, applied to several actual datasets of ELISA assay data, we consider the robustness of normal parametric methods, e.g. t tests and linear regression. Despite the skewness of the transformed data, we demonstrate that such methods are quite robust depending on the number of observations, type of analysis and severity of skewness. We also illustrate how bootstrap resampling can be used to provide a valid alternative method of analysis that can be used either for checking normal parametric analysis or as a direct method of analysis. We illustrate this combined approach by analysing real data to test for association between human serum antibodies to malaria merozoite surface proteins, MSP1 and MSP2, and resistance to clinical malaria, and confirm the protective effect of antibodies to MSP1 and demonstrated a similar protective effect for some antibodies to MSP2.
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PMID:Statistical analysis of highly skewed immune response data. 903 13

Malaria remains one of the major health problems in many tropical countries. Plasmodium falciparum is the most common malaria parasite in Africa, and it causes much more severe and progressive illness than any of the other types of malaria parasite. Children living in sub-Saharan Africa are bearing the major burden of the disease and the mortality. Whatever parameter is used to measure the mortality or the morbidity from malaria, the true problem is likely to be underestimated. The pattern of morbidity and mortality depends on the transmission intensity; the more intensity of malaria transmission is increased, the earlier and more confined the age range of symptomatic malaria. The asymptomatic carrier status is common, and 60-80% of the children in highly endemic areas have P. falciparum parasitaemia at any given time. Consequently a case definition based on the mere presence of parasites in the blood is non-informative in terms of measuring morbidity. Recognizing that there are no specific diagnostic clinical parameters for malaria, but that fever is very common, and that morbidity is to some extent dependent on the parasite density, we described using a logistic regression model the probability of being sick from malaria in relation to body temperature and parasite density. Acquired clinical and parasitological immunity develop progressively over several years after repeated exposure to infection. Protection is acquired first against death or severe clinical disease, then against milder clinical attacks, but protection against infection is never complete. Clinical and parasitological immunity develop concomitantly, as demonstrated by relating the parasite densities to measured body temperature. However, the ability to control the disease and parasite density develops earlier than the ability to prevent the parasite infection. The individual immune mechanisms that are responsible for the acquired immunity remain uncertain, but classical transfer experiments with polyvalent gamma globulin from immune donors to non-immune individuals showed that antibodies play an important role. Potential targets for malarial vaccines include antigens on the surface of the sporozoites and the merozoites. Several protein antigens from P. falciparum have been characterized at the molecular level, and most of the characterized antigens have the common characteristic that they are recognized by immune sera from individuals living in malaria endemic areas. Working on the approach that potentially useful targets for protective vaccine development can be identified by correlating the naturally acquired immune responses with defined P. falciparum antigens, we examined antigens from both the sporozoite stage (CS-protein) and the blood stages (Pf155/RESA, GLURP, and MSP1), as well as P. falciparum induced neoantigens on the red blood cell (band-3 neoantigens). The relationship between the immune response to these defined P. falciparum antigens and clinical and parasitological protection was analysed in the individual age groups. The contribution of the antigen-specific immune response was evaluated, and a positive correlation of parasite density or probability of an episode of clinical malaria with antibody response to the individual antigens was identified in defined age groups. This correlation, however, did not span all age groups, and thus overall responses to defined antigens are not considered to be reliable indicators of protection. The findings may contribute to the understanding of immunological and clinical host responses to parasitaemia and to defined P. falciparum antigens. The studies on the impact of asexual stage infection and the human immune response led to studies on specific and non-specific responses to P. falciparum blood-stage parasites and observations on gametocytaemia. We demonstrated that pyrimethamine/sulfadoxine and chloroquine did not induce gametocytogenesis as suggested previously, but preformed gametocytes persisted after
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PMID:Clinical and parasitological studies on immunity to Plasmodium falciparum malaria in children. 906 51

A successful anti-blood stage malaria vaccine trial based on a leading vaccine candidate, the major merozoite surface antigen-1 (MSP1), is reported here. The trial was based on Plasmodium cynomolgi, which is a primate malaria parasite which is highly analogous to the human parasite Plasmodium vivax, in its natural host, the toque monkey, Macaca sinica. Two recombinant baculovirus-expressed P. cynomolgi MSP1 proteins, which are analogous to the 42- and 19-kDa C-terminal fragments of P. falciparum MSP1, were tested by immunizing three groups of three animals each with either p42, p19, or both together. The vaccines were delivered subcutaneously in three doses at 4-week intervals with complete and incomplete Freund's adjuvants. Very high antibody titers were obtained against both vaccinating antigens as measured by enzyme-linked immunosorbent assay (10[6] and above) and against whole parasites as measured by indirect immunofluorescence assay (>10[5]), achieving, in most animals, about a 10-fold increase from the first to the last immunization. A blood stage challenge with P. cynomolgi parasites led, in three adjuvant-treated and three naive control animals, to blood infections which were patent for at least 44 days, reaching peak densities of 0.6 and 3.8%, respectively. In contrast, all except one of the nine animals in the three vaccinated groups were highly protected, showing either no parasitemia at all or transient parasitemias which were patent for only 1 or 2 days. When the three p19-vaccinated monkeys were rechallenged 6 months later, the protective efficacy was unchanged. The success of this trial, and striking analogies of this natural host-parasite system with human P. vivax malaria, suggests that it could serve as a surrogate system for the development of a human P. vivax malaria vaccine based on similar recombinant analogs of the P. vivax MSP1 antigen.
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PMID:Baculovirus merozoite surface protein 1 C-terminal recombinant antigens are highly protective in a natural primate model for human Plasmodium vivax malaria. 952 73

MSP1(19) is one of the leading malaria vaccine candidates. However, the mechanism of protection is not clear. To determine whether MSP1(19)-specific effector T cells can control parasitaemia, we analysed the specificity of T cells induced following immunization with recombinant forms of P. yoelii MSP1(19) and asked whether they could protect mice. There was no evidence that effector T cells were capable of protecting since: (1) immunization of mice with yMSP1(19), but not defined epitopes, was able to induce protection; and (2) long term MSP1(19)-specific CD4+ T cell lines were incapable of adoptively transferring protection. In contrast, priming mice with the T cell epitopes resulted in a rapid anamnestic antibody response to MSP1(19) after either challenge with MSP1(19) or parasite. Thus, MSP1(19) contains multiple T cell epitopes but such epitopes are the targets of helper T cells for antibody response but not of identified effector T cells capable of controlling parasitaemia.
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PMID:Definition of T cell epitopes within the 19 kDa carboxylterminal fragment of Plasmodium yoelii merozoite surface protein 1 (MSP1(19)) and their role in immunity to malaria. 965 28

Specific immune responses to asexual blood stages of P. falciparum antigens (a lysate of parasitized red blood cells and a characterized vaccine candidate i.e. MSP1 p19) were analyzed in plasma samples from immune adult individuals living in three different areas of Senegal, where malaria transmission is different. Most individuals in the three sites had specific IgG and IgM to total P. falciparum antigens, whereas approximately 50% had either IgG or IgM specific to MSP1 p19. Further, no anti-MSP1 p19 IgG2 and IgG4 antibody was noticed in any individual whereas the distribution of anti-MSP1 p19 IgG1 and IgG3 was different upon the epidemiological context. In addition, no relationship was found between antibody responses and in vitro T cell responses against P. falciparum antigens upon those experimental conditions. These data stress on the relatively elevated distribution of specific antibodies to MSP1 p19 in P. falciparum hyperendemic areas and suggest a differential regulation of isotypes depending on individual parasite exposure.
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PMID:[Specific antibodies against Plasmodium falciparum antigens in immune subjects: II. Screening of responses against the merozoite major surface antigen (MSP!)]. 982 30


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