Biomedical subjects

E M Riley

Publications and source records attributed to E M Riley.

At least 55 records · Page 3Linked to original sources

PubMed1993

Soluble plasma IL-2 receptors and malaria.

Plasma levels of soluble IL-2 receptor (sIL-2R) were measured by immunoassay in 180 individuals, aged 1-70 years, living in a malaria-endemic community in West Africa. sIL-2R levels were compared with age, malaria parasitaemia, malaria-associated morbidity and cellular immune responses to Plasmodium falciparum antigens. Plasma levels of sIL-2R were independently associated with both age and patent malaria parasitaemia. No significant association was observed between IL-2R levels and concurrent malaria morbidity (i.e. fever associated with malaria), but the number of individuals with clinical malaria at the time of sampling was small. Although there was no association between plasma sIL-2R levels and in vitro proliferative responses of peripheral blood mononuclear cells (PBMC) to a number of defined malaria antigens, we did find a significant negative association between sIL-2R and in vitro proliferation of unstimulated PBMC. High levels of sIL-2R (up to 5500 U/ml) were detected in the plasma of malaria-infected individuals; this is indicative of a vigorous cellular immune response to malaria antigens in vivo and does not support the notion that malaria infections are generally immunosuppressive. Indeed, we found that, at the low levels of parasitaemia present in study subjects, there was no significant difference in the mean proliferative response to malaria antigens in infected subjects when compared with uninfected subjects.

Adolescent↗

PubMed1993

Lymphoproliferative responses to a merozoite surface antigen of Plasmodium falciparum: preliminary evidence for seasonal activation of CD8+/HLA-DQ-restricted suppressor cells.

We have investigated the phenotype of human lymphocytes responding to a defined Plasmodium falciparum malaria antigen in vitro. Cells were obtained from the peripheral blood of malaria-immune donors from an endemic area of West Africa and were tested for proliferation in response to cloned fragments of a merozoite surface protein (PfMSP1). Depletion and inhibition studies indicated that the majority of proliferating cells were CD4+ and restricted by HLA-DR or -DQ. A proportion of responding cells appeared to be CD8+, but their response was dependent on help from CD4+ cells. In two donors there was evidence that low responses could be enhanced by removal of CD8+ cells and/or blocking of antigen presentation by anti-HLA-DQ antibodies. This phenomenon was observed in cells collected during the wet (malaria transmission) season but not in cells collected from the same individual during the dry season.

Adolescent↗

PubMed1993

A longitudinal study of naturally acquired cellular and humoral immune responses to a merozoite surface protein (MSP1) of Plasmodium falciparum in an area of seasonal malaria transmission.

A longitudinal study of cellular and serological responses to the major merozoite surface protein of Plasmodium falciparum (PfMSP1) has been conducted in a malaria immune population living in The Gambia, where malaria transmission is seasonally endemic. Recombinant or native proteins representing the sequence of PfMSP1 from the Wellcome strain of P. falciparum were used in in vitro lymphocyte proliferation, cytokine and antibody assays. Cellular responses of individual donors fluctuated over time, independent of seasonal changes in malaria transmission whereas anti-PfMSP1 antibody levels were remarkably stable. At a population level, IFN gamma responses were both more prevalent and of greater magnitude at the end of the rainy (malaria transmission) season than during the dry season. Responses of individuals living in a rural village were compared with those of individuals living in an urban area with much lower levels of malaria transmission. Malaria infections were more likely to be symptomatic in urban dwellers than in inhabitants of rural villages but no significant differences in the level or prevalence of cellular or serological responses were seen between the two groups. However, urban dwellers with current symptomatic malaria infections had somewhat lower anti-PfMSP1 antibody levels than their healthy, non-parasitaemic neighbours.

Adolescent↗

PubMed1993

Immunoglobulin M and G antibody responses to Plasmodium falciparum glutamate-rich protein: correlation with clinical immunity in Gambian children.

The aims of the present study were to describe the age-related immunoglobulin M (IgM) and IgG response to part of a 220-kDa glutamate-rich protein (GLURP) from Plasmodium falciparum and to determine possible correlations of possession of these antibodies with malaria morbidity. IgM and IgG levels were measured with a recombinant fusion protein consisting of the carboxy-terminal 783 amino acids of the GLURP. Samples for the study were obtained during a longitudinal malaria morbidity survey performed in The Gambia; cross-sectional surveys were performed at the beginning of the transmission season in May and in October. Seropositivity rates increased with age to a maximum of 77% for IgM and 95% for IgG in adults. High prevalences of seropositivity were associated with certain human leukocyte antigen class II alleles (DRw8, DR9, DR7, DR4, DQw7, and DQw2) or haplotypes. The relationship between anti-GLURP489-1271 antibodies and clinical immunity is not clear; asymptomatically infected children aged 5 to 8 years had significantly higher levels of IgG than clinically ill children of the same age, suggesting that antibodies to the carboxy-terminal part of the GLURP may contribute to immunity to P. falciparum. However, this was not significant for younger children.

Adolescent↗

PubMed1992

Isolation of maternal mononuclear cells from placentas for use in in vitro functional assays.

Interest in immunoregulatory mechanisms within uteroplacental tissues, particularly in malarial infection during pregnancy, prompted us to develop a technique to extract maternal mononuclear cells from human term placentas. This method is described. The phenotypes of isolated cells were characterised for expression of CD45, CD3, CD4, CD8, CD14, CD15, CD68, CD22, CAM 5.2 and class II MHC antigens and compared with those in situ in frozen sections of the same placentas. Isolated mononuclear cell preparations were examined for contamination by fetal trophoblasts. Fetal leukocyte contamination appeared unlikely since histological sections of placental tissue, after the extraction of maternal leukocytes, showed intact chorionic villi with no disruption of fetal stem vessels. This technique produces preparations of maternal placental mononuclear cells which are representative of cells in situ, show minimal fetal cell contamination and are suitable for functional studies.

Antibodies, Monoclonal↗

PubMed1992

The statistical analysis of data from immunoepidemiological studies.

Immune responses encountered in human populations display a higher level of heterogeneity than is typically seen with laboratory animals, and the expected clear distinction between responders and non-responders to particular antigens may not be apparent. In such a situation, the methods of statistical analysis traditionally used in laboratory studies may no longer be appropriate, and there is no consensus among immunologists about how such data should be analysed. Using data from a large study of lymphocyte proliferation responses to candidate antigens for a vaccine against Plasmodium falciparum malaria, we discuss questions such as the appropriateness of logarithmic transformation of the data, the use of the stimulation index versus delta--cpm, the use of the proportion of responders for comparing two groups of individuals, and the choice of threshold for defining such a responder.

Animals↗

PubMed1992

MHC and malaria: the relationship between HLA class II alleles and immune responses to Plasmodium falciparum.

In mice, immune responses to subunits of defined malaria antigens are regulated by genes mapping within the MHC and it has been suggested that such genetic restriction will be a major obstacle in the development of a human malaria vaccine. The relationship between class II human leukocyte antigen (HLA) genes and immune recognition of three candidate antigens for a vaccine against Plasmodium falciparum malaria has been investigated in a human population living in a malaria endemic area of West Africa. The study population was shown to be extremely heterogeneous for HLA class II alleles and marked differences in allelic frequency were detected between members of different ethnic groups. One class II DQA-DQB combination (serological specificity DQw2) was particularly common among members of the Fula ethnic group. This haplotype was significantly associated with higher than average levels of antibody to a peptide epitope, (EENV)6, of the malaria antigen Pf155/RESA. There was little evidence of association between HLA class II genotype and cellular proliferative or interferon gamma responses to the antigens tested. Overall, the number of significant associations between immune responses and specific HLA class II haplotypes was greater than would be expected by chance but less than would be expected if class II-dependent genetic restriction were a major factor governing human immune responses to malaria antigens. Thus, although some qualitative variation in the immune response to vaccine antigens may occur in ethnically different target populations, widespread HLA-associated nonresponsiveness to a multivalent subunit malaria vaccine is unlikely.

Adolescent↗

PubMed1992

Severe malaria in Gambian children is not due to lack of previous exposure to malaria.

The reasons why only a small proportion of African children infected with Plasmodium falciparum develop severe or fatal malaria are not known. One possible reason is that children who develop severe disease have had less previous exposure to malaria infection, and hence have less acquired immunity, than children who develop a mild clinical attack. To investigate this possibility we have measured titres of a wide range of anti-P. falciparum antibodies in plasma samples obtained from children with severe malaria, children with mild malaria and from children with other illnesses. Mean antibody levels in patients with malaria were higher than those in patients with other conditions but, with only one exception, there were no significant differences in antibody titres between cases of severe or mild malaria. A parasitized-erythrocyte agglutination assay was used to estimate the diversity of parasite isolates to which children had been exposed; plasma samples obtained from children with cerebral malaria recognized as many isolates as did samples obtained from children with mild disease. Our findings do not provide any support for the view that the development of severe malaria in a small proportion of African children infected with P. falciparum is due to lack of previous exposure to the infection.

Animals↗

PubMed1992

Naturally acquired cellular and humoral immune responses to the major merozoite surface antigen (PfMSP1) of Plasmodium falciparum are associated with reduced malaria morbidity.

We have investigated the pattern of acquired immune responses to the major surface protein of Plasmodium falciparum merozoites (gp 190, PfMSP1) in a malaria endemic population in West Africa. A prospective longitudinal study in 3- to 8-year-old children was conducted to examine the relationship between naturally acquired immune responses to PfMSP1 and subsequent susceptibility to malaria infection and clinical disease. A population cross-sectional survey was performed to investigate changes in immune response with age. The prevalence and concentration of antibodies to all regions of the molecule increased with age with the highest prevalence of antibodies being detected against regions of the molecule which are highly conserved between parasite isolates. In vitro lympho-proliferation and interferon-gamma production in response to recombinant proteins representing polymorphic regions of the molecule also increased with age. Interestingly, proliferative responses to some regions of the molecule, including some highly conserved sequences, were highest in young children and decreased markedly with increasing age. Significant associations were observed between antibody and lymphoproliferative responses to proteins from the C terminus of the molecule and resistance to episodes of fever associated with high parasitaemia in partially immune children. In addition, high concentrations of antibodies to a conserved region close to the N terminus of PfMSP1 were also significantly associated with protection.

Africa, Western↗

PubMed1991

HLA-DR and -DQ gene polymorphism in West Africans is twice as extensive as in north European Caucasians: evolutionary implications.

The HLA genes are the most polymorphic coding loci known in humans. DRB-DQA-DQB gene polymorphism was investigated by Taq I restriction fragment length polymorphism analysis in more than 700 West Africans and found to be almost twice as extensive in West Africans as in North European Caucasians. This finding indicates that Africans comprise the oldest and genetically most diverse human population and supports the hypothesis of the occurrence of a population bottleneck in the emergence of the White race. As in Caucasians, less than one-third of possible cis-encoded DQA-DQB combinations were encountered, indicating constraints on the pairing of DQ alpha and beta polypeptides. Heterozygote advantage (i.e., positive selection) was found for DRB, DQA, and DQB alleles as well as for DQA-DQB combinations. However, in West Africans as well as in North Europeans the observed frequencies of DRB-DQA-DQB homozygotes were close to neutrality expectations. Although the hypothesis that HLA polymorphism is maintained by parasite-driven overdominant selection is attractive, there is little evidence to support that view. We propose instead that one of the forces maintaining a low frequency of HLA homozygotes might be a decreased likelihood of potentially autoreactive T-cell clones escaping thymic selection in HLA heterozygotes. This would be consistent with the central role of HLA molecules as self/non-self discriminators.

Africa, Western↗

PubMed1991

Immune response to soluble exoantigens of Plasmodium falciparum may contribute to both pathogenesis and protection in clinical malaria: evidence from a longitudinal, prospective study of semi-immune African children.

Some soluble exoantigens of Plasmodium have lipopolysaccharide (LPS)-like properties and are believed to contribute to the pathogenesis of acute malaria. We have studied cellular and humoral immune responses to several purified exoantigens of Plasmodium falciparum in a cohort of children and compared these responses with their subsequent susceptibility to malaria infection and clinical disease. We found no evidence that either lymphoproliferative or interferon-gamma (IFN-gamma) responses to these antigens were associated with protective immunity. On the contrary, children whose cells produced IFN-gamma after in vitro activation with one of the soluble antigens (Ag7) were more likely to experience clinical manifestations of malaria infection (fever and malaise) than were children whose cells did not produce IFN-gamma. It is possible that exoantigen-induced IFN-gamma may exacerbate the LPS-like effects of these antigens. However, serum antibodies to another antigen (Ag2) were more prevalent in children with asymptomatic infections or low parasitemia than in children with fever and higher parasitemia (confirmed clinical malaria), suggesting that these antibodies may contribute to the development of protective immunity.

Animals↗

PubMed1991

The immune recognition of malaria antigens.

Owing to the demonstration that the immune response of inbred mice to some defined malaria antigens is influenced by the major histocompatibility complex (MHC), and the finding that only a minority of individuals living in malaria-endemic areas appear to recognize such antigens, there are fears that synthetic subunit malaria vaccines will be poorly immunogenic in a substantial proportion of the target population. Such fears have been reinforced by the results of the first two human malaria vaccine trials. In this review Eleanor Riley, Olle Olerup and Marita Troye-Blomberg summarize the experimental evidence for MHC-related genetic restriction of malaria immunity and discuss some alternative explanations for nonresponsiveness in populations living in malaria-endemic areas.

Journal Article↗

PubMed1991

Isolation and characterization of a soluble antigen complex of Plasmodium falciparum with pyrogenic properties.

A soluble antigen complex, previously designated antigen no. 7 (Ag7) on the basis of the pattern obtained by crossed immunoelectrophoresis of culture supernatants of P. falciparum, was isolated by affinity chromatography. It was shown to be synthesized at the schizont stage of the parasite growth cycle and to be located on the surface of the schizonts. Antibodies to Ag7 did not inhibit the growth of the parasite in vitro. Ag7 is recognized by immune human sera from many parts of the world and it stimulated the production of specific antibody in mice when incorporated into immune-stimulating complex (ISCOM) structures. It also specifically stimulated in vitro proliferation of lymphocytes from clinically immune adults. That it induced the secretion of interleukin 1 by human monocytes and was pyrogenic in rabbits was of particular interest. Thus Ag7 has endotoxin-like properties which make it a possible candidate for an antitoxic malaria vaccine.

Animals↗

PubMed1990

Cellular and humoral immune responses to Plasmodium falciparum gametocyte antigens in malaria-immune individuals. Limited response to the 48/45-kilodalton surface antigen does not appear to be due to MHC restriction.

We have examined immune responses to a cultured Plasmodium falciparum gametocyte lysate and to an affinity-purified preparation of the 48/45-kDa gamete surface Ag in a group of 30 malaria immune individuals and in 24 Europeans with no previous exposure to malaria. Cellular responses were assessed in vitro by lymphoproliferation and production of IFN-gamma; antigamete antibodies were detected by immunofluorescence, Western blotting, and competitive ELISA. Cells from all the malaria immune donors responded to the gametocyte lysate in both assays while cells from nonimmune donors gave only weak proliferative responses. Antigamete antibodies were detected in the serum of all the immune donors but not in serum from nonimmunes. Nonimmune donors were completely unresponsive to the purified 48/45-kDa surface Ag while cells from 40% of immune donors responded by either proliferation or IFN-gamma production. Only 3 of 30 immune donors had detectable antibodies to the 48/45-kDa Ag. Class II HLA type was determined for 27 of the immune donors but no relationship between HLA-DR or -DQ and responsiveness to the 48/45-kDa Ag was discerned. The possible reasons for limited recognition of this gamete surface Ag are discussed.

Animals↗

PubMed1990

Biochemical characterization, localization and immunostimulating properties of a soluble glycoprotein, Ag1, isolated from in vitro cultures of Plasmodium falciparum.

The soluble amphiphilic glycoprotein, Ag1 (gp60), purified from supernatants of in vitro cultures of Plasmodium falciparum has a molecular mass of 60 kDa and did not exhibit size variation in the different P. falciparum isolates tested by immunoblotting. Ag1 was shown to interact with the lectin Erythrina christagalli agglutinin, which is specific for carbohydrates bearing beta-D-galactose(1-4)-D-N-acetylglucosamine. Indirect immunofluorescence studies showed that Ag1 is located on the surface of trophozoites and schizonts but not on the surface of merozoites. Ag1 is recognized by human immune sera from six different malaria-endemic regions. Ag1 induces in vitro proliferation of lymphocytes from malaria-immune individuals in an antigen-specific manner.

Animals↗

PubMed1990

Characterization of regulatory T cell responses to defined immunodominant T cell epitopes of the Plasmodium falciparum antigen Pf155/RESA.

Several immunodominant B and T cell epitopes of the P. falciparum blood stage antigen Pf155/RESA, a vaccine candidate, are located in the central (5') and C-terminal (3') invariant repeat regions of the molecule. Here we have attempted to functionally analyze human T cell responses to some of the T cell epitopes. For this purpose short synthetic peptides corresponding to these epitopes were used to study the induction of in vitro expression of IL-4 mRNA, IFN-gamma secretion, proliferation and B cell help for antibody production. In individual malaria immune donors these different T cell activities were not correlated. The findings emphasize the importance of examining multiple parameters of T cell activation when estimating the total proportion of individuals responding to a defined antigen. IL-4 mRNA was expressed in activated T cells of donors who had elevated serum concentrations of antibodies to the peptide used for T cell activation. These results suggest the involvement of IL-4 producing T helper cells in the induction of Pf155/RESA specific antibody production in individuals in which immunity has been induced by natural infection. Taken together, these findings also suggest that functionally distinct CD4+ T cells occur in humans similarly to what has been described in mice. In further experiments, we have also attempted to establish MHC class II restriction of the immune response to these epitopes at the level of the donor populations. When studying monozygotic twins, antibody responses to Pf155/RESA derived peptides and some of the T cell responses could be paired within the twin pairs, indicating a genetic regulation of their B cell responses. Whether or not this regulation reflects MHC class II restriction, or other factors needs to be elucidated.

Amino Acid Sequence↗

PubMed1990

Praziquantel treatment of Biomphalaria glabrata infected with Schistosoma mansoni--influence on snail fecundity.

Praziquantel, administered over a 72 h period in the food of mature Biomphalaria glabrata harbouring 7-week-old Schistosoma mansoni infections, dramatically reduced the numbers of cercariae shed. Doses of 20-30 micrograms/g body weight (including shell weight) reduced shedding by 85-95% over 5 weeks before recovery was evident. Suppression of cercarial shedding in these infections was accompanied by the temporary recovery of the snail reproductive regression due to S. mansoni infection. Snail fecundity was subsequently re-suppressed 2 weeks prior to recovery of the parasite as evidenced by a resumption of cercarial shedding. Praziquantel destroyed mature and developing cercariae within the daughter sporocysts but had no apparent effect on daughter sporocysts; this may account for the eventual resumption of cercarial production. Reproductive failure of the snail is apparently related to the latter stages of cercarial development specifically. Reproductive recovery did not occur when snails were infected as juveniles or when mature-infected snails harboured 12.5 week i.e. older infections: drug treatment temporarily inhibited cercarial production but no snails produced eggs.

Animals↗

PubMed1990

Production by activated human T cells of interleukin 4 but not interferon-gamma is associated with elevated levels of serum antibodies to activating malaria antigens.

T cells play a crucial role in antibody-mediated and antibody-independent immunity against Plasmodium falciparum malaria. Therefore, a vaccine immunogen should include parasite-derived B- and T-cell epitopes capable of giving rise to protective responses in both systems. The P. falciparum antigen Pf155/ring-infected erythrocyte surface antigen (RESA), a vaccine candidate, contains immunodominant T- and B-cell epitopes located in the central (5') and C-terminal (3') invariant repeat regions of the molecule. To relate Pf155/RESA-peptide-specific responses of T cells to function, T cells from P. falciparum immune donors were activated with peptides corresponding to these immunodominant regions. Activation was measured as induction of interferon-gamma secretion, T-cell proliferation (DNA synthesis), or transcription and translation of interleukin 4 (IL-4) mRNA. Peptides from both regions were shown to induce interferon-gamma, IL-4, proliferation, or any combination. In individual donors, there was no correlation between these different activities. Rather, they were negatively correlated, demonstrating the importance of examining multiple parameters of T-cell activation when estimating the proportion of individuals responding to a given epitope. However, IL-4 mRNA and intracellular IL-4 could be induced in T cells of donors who had elevated concentrations of serum antibodies to the same peptide that was used for T-cell activation. These results suggest that a causal relationship exists between the activation of IL-4-producing T-cell subsets and production of the anti-Pf155/RESA-specific antibodies in individuals in which immunity has been induced by natural infection. This finding has implications that should be considered for the selection of immunogens to be included in a future P. falciparum subunit vaccine and for vaccine development in general.

Adult↗