Biomedical subjects

M Troye-Blomberg

Publications and source records attributed to M Troye-Blomberg.

At least 73 records · Page 4Linked to original sources

PubMed1996

Immunoglobulin E elevation in Plasmodium chabaudi malaria.

In order to investigate the mechanism of immunoglobulin E (IgE) elevation in malaria we studies mice infected with asexual blood stages of the rodent malaria parasite Plasmodium chabaudi chabaudi for total IgE and IgE antimalarial antibodies. Multiply infected mice had elevated levels of total as well as malaria-specific IgE in their sera. Sera taken from mice 3 weeks after one infection with P. chabaudi showed no IgE elevation, indicated that prolonged or repeated exposure to the parasite is necessary for the induction of an IgE response, which also is induced independently of previous or simultaneous infection with other pathogens such as helminths.

Animals↗

PubMed1995

Cytokine profiles for human V gamma 9+ T cells stimulated by Plasmodium falciparum.

V gamma 9+ T cells from malaria non-exposed donors make proliferative responses to Plasmodium falciparum on in vitro stimulation. V gamma 9+ cells are strongly activated by components of the schizont stage of the parasite and by antigens released into the culture upon schizogony, while CD4+V gamma 9- cells are stimulated by the earlier stages of the parasite. Using reverse transcriptase-polymerase chain reaction (RT-PCR) we determined mRNA expression for 14 cytokines in highly purified V gamma 9+ cells enriched by positive selection after in vitro stimulation with P. falciparum schizont antigens. Interferon-gamma (IFN-gamma) and Tumor Necrosis Factor-alpha (TNF-alpha) were detected in all samples tested. The majority of samples also expressed TNF-beta, transforming growth factor-beta (TGF-beta) and Interleukin-8 (IL-8). Only occasional samples expressed IL-2, IL-5 and IL-10. Using the ELISPOT assay we found that a large fraction of the reactive V gamma 9+ cells produced IFN-gamma and that gamma delta T cells are the major producers of IFN-gamma in cultures stimulated with schizont antigens. The majority of V gamma 9+ cells in these cultures also express the membrane-bound form of TNF-alpha. Expression of these cytokines speaks for a cytolytic and/or inflammatory role of gamma delta cells in the response to malaria in non-exposed individuals.

Adult↗

PubMed1995

Comparison of the number of IL-4 and IFN-gamma secreting cells in response to the malaria vaccine candidate antigen Pf155/RESA in two groups of naturally primed individuals living in a malaria endemic area in Burkina Faso.

The enzyme-linked immunospot (ELISPOT) assay was used to enumerate the number of IFN-gamma and IL-4 producing cells after in vitro stimulation with a highly purified recombinant malaria vaccine candidate antigen (r-Pf155/RESA) or synthetic peptides corresponding to its major T-cell epitopes. Two groups of naturally primed individuals living in rural areas of Burkina Faso were studied. The donors comprised one group of healthy (non-parasitemic) mainly adult people and one parasitemic mainly younger people. IL-4 producing cells were detected in response to PHA but no such cells were detected in response to the malarial antigens. The most frequent IFN-gamma responses were seen with r-Pf155/RESA. Thus, after stimulation with this antigen 52% of the donors responded positively in the ELISPOT assay, while only 17% responded to the synthetic peptides, suggesting that the rPf155/RESA contained T-cell epitopes not covered by the peptides used in this study. The number of IFN-gamma producing cells in response to the malarial antigens did not differ between the two groups. However, IFN-gamma levels found in sera from the parasitemic individuals were significantly higher than in those from healthy donors. This latter finding and the lack of differences seen in the number of IFN-gamma producing spots in the two groups indicate that IFN-gamma producing cells may have sequestered to other organs in the parasitemic group.

Adolescent↗

PubMed1994

Cytokine synthesis analyzed at the single-cell level before and after revaccination with tetanus toxoid.

Tetanus toxoid (TT) is a potent immunogen which evokes strong antibody responses after immunization. Here, TT was used as a model antigen to study the production of cytokines at the single-cell level during the in vitro immune response to a specific recall antigen. Peripheral blood mononuclear cells were obtained from healthy volunteers before and 9 weeks after TT vaccination and were cultured with antigen in vitro. The kinetics of cytokine synthesis as well as frequencies of cytokine-producing cells were determined at the single-cell level by immunofluorescent intracellular staining of the cytokine protein. The phenotype of the producer cells was revealed by concomitant staining of surface markers. Two patterns of cytokine synthesis were induced by TT: (i) T lymphocytes expressed a number of lymphokines (interleukin (IL)-2, IL-3, IL-4, IL-10, interferon (IFN)-gamma and tumor necrosis factor (TNF)-beta), each with distinct kinetics of synthesis. This cytokine expression was strictly dependent on the previous exposure of the donor to TT and positively correlated with the level of tetanus immunity, as judged by TT-specific Ab levels in plasma as well as lymphoproliferation. Cells producing IL-2, IFN-gamma and particularly TNF-beta dominated this in vitro response. After 96-120 h in culture, 1.0-1.3% of the cells produced TNF-beta, i.e. frequencies at least tenfold higher than for any of the other lymphokines assayed. The addition of IL-2 to the cultures caused a fourfold increase and a kinetics shift in the production of TNF-beta, which peaked already at 24 h. Exogenously added IL-2 also caused a five- to tenfold increase in the number of IL-2 and IFN-gamma producers but no apparent change in the kinetics of intracellular lymphokine appearance. (ii) The cytokines IL-1 alpha, IL-1 beta, IL-6 and TNF-alpha were produced by monocytes. This inflammatory monokine response was independent of the TT-specific immune status of the donors, characterized by a rapid onset and was transient.

Adult↗

PubMed1994

Presentation of the Plasmodium falciparum antigen Pf155/RESA to human T cells. Variations in responsiveness induced by antigen presenting cells from different but MHC class II identical donors.

The antibody response in humans naturally primed to a malaria vaccine candidate antigen (Pf155/RESA) is genetically regulated. Here, the impact of antigen presenting cells (APC) on the control of in vitro T-cell responses induced by Pf155/RESA or synthetic peptides corresponding to its major Pf155/RESA epitopes was studied. T cells and APC were from the peripheral blood of monozygotic or dizygotic twins and their age matched siblings, all living in the central highlands of Madagascar. When induced to proliferate (thymidine incorporation) in vitro by antigenic peptides, the T-cell responses varied less within the twin pairs than between them and their siblings or the entire group, implying that they were genetically regulated. Occasional MHC class II associations of some of the responses were weak and did not reflect underlying MHC class II restrictions. When T cells and APC from different but MHC class II identical donors were incubated in various combinations, antigen charged APC from homologous donors induced in vitro T-cell proliferation which differed from that induced by the T-cell donors' own APC. Pretreatment of the APC with either paraformaldehyde or anti-class II antibodies inhibited or abolished this antigen dependent T-cell proliferation. The results suggest that the observed differences in T-cell responses induced by APC from different donors reflect differences at the level of these cells. Whether they reflect differences in the proteases involved in antigen processing, in the costimulatory signals provided by the APC to the T cells or in the secretion of other regulatory factors remains to be elucidated.

Adolescent↗

PubMed1994

Human T-cell responses to blood stage antigens in Plasmodium falciparum malaria.

Immunity to malaria involves both cell-mediated and humoral immune mechanisms. T cells are essential both in regulating antibody formation and in inducing antibody-independent immunity. Thus, acquisition and maintenance of protective immunity to malaria is T-cell dependent. Although relatively neglected until recently basic knowledge of T-cell subsets and cytokine production determining the course of a malaria infection is advancing rapidly at present. In this paper we will review recent findings contributing to the understanding of immune mechanisms against the asexual blood stages of human P. falciparum malaria.

Animals↗

PubMed1994

IgE elevation and IgE anti-malarial antibodies in Plasmodium falciparum malaria: association of high IgE levels with cerebral malaria.

In the course of studying immunoregulation in human Plasmodium falciparum malaria we have investigated IgE levels and IgE anti-plasmodial antibodies in children and adults from areas of high malaria endemicity in both Africa and Asia. On average, 85% of all donors had significantly elevated levels of total IgE. A fraction of the IgE had anti-plasmodial activity as revealed by ELISA with lysates of infected erythrocytes as antigen. Using synthetic peptides representing antigenic regions of two major plasmodial blood stage antigens, IgE antibody concentrations ranged from 5 to 15 ng/ml serum for each of the peptides. On average, the concentrations of the corresponding IgG antibodies were x 500-1000 higher. Immunoblotting of parasite lysates showed that most donors had IgE antibodies against one or several of a restricted number of plasmodial polypeptides, with antibodies against an antigen of mol.wt 45 kD already being present in all donors at an early age. Donors having IgE antibodies to particular antigens also frequently had corresponding IgG4 antibodies, reflecting underlying IL-4-dependent cellular mechanisms controlling formation of these isotypes. As infection with other parasites such as helminths is known to induce IgE elevation, the results do not prove that plasmodial infections were the primary cause of IgE induction. However, the importance of plasmodial infection for IgE elevation was supported by the finding of significantly higher levels of IgE, but not of IgG, in children with cerebral malaria compared with patients with uncomplicated disease.

Adolescent↗

PubMed1994

Human monocytes cultured with and without interferon-gamma inhibit Plasmodium falciparum parasite growth in vitro via secretion of reactive nitrogen intermediates.

Adherent cells from human peripheral blood were studied for their interaction with asexual blood forms of Plasmodium falciparum in vitro. Freshly isolated monocytes only showed weak anti-parasitic effects. However, an enhancement of this anti-parasitic activity was apparent when monocytes were allowed to mature in vitro. Monocytes activated with IFN-gamma for two or three days had an enhanced anti-parasitic effect. In contrast, the inhibition mediated by cells incubated for five days was the same with or without IFN-gamma treatment. There was no evidence of toxicity when IFN-gamma at high concentrations was added directly to P. falciparum cultures. The anti-parasitic activity of the activated cells seemed to be due to nitric oxide since incubation of macrophages with L-NMMA reduced the level of inhibition. However, inhibition was only partial suggesting that other factors also were involved in inhibition of parasite growth.

Animals↗

PubMed1994

Immunosuppression after measles vaccination.

The influence of conventional live attenuated measles vaccine on cellular immune responsiveness was investigated in Sweden and Guinea-Bissau. Sixteen children in a residential area in Bissau and 16 living in southern Stockholm were examined before and 8-10 days after vaccination. Lymphoproliferation was measured to concanavalin A (con-A), PPD and tetanus toxoid (TT) using a whole-blood 3H-thymidine incorporation assay. Stimulation indices were significantly lower after vaccination than before, in the case of con-A (p = 0.03) and TT (p = 0.01) in the Guinean children and in the case of PPD (p = 0.009) and TT (p = 0.03) in the Swedish children. Stimulation of lymphocytes from measles-immune children with measles antigens resulted in weak lymphoproliferative responses. These observations may be relevant to the increased mortality found in children immunized with high-titre measles vaccines, as compared to controls, in recent studies. The study confirms the applicability and usefulness under field conditions of the whole blood version of the thymidine incorporation assay.

Child, Preschool↗

PubMed1994

T-cell control of immunity to the asexual blood stages of the malaria parasite.

Both antibody-dependent and antibody-independent mechanisms are involved in immune protection against the asexual blood stages of the malaria parasite. It is well established that T cells play a crucial role in both induction and maintenance of this immunity. Of the two T-cell subsets (CD4+, CD8+) carrying alpha/beta T-cell receptors, the CD4+ T cells are of major importance for the development of blood stage immunity in both experimental and human malaria. In mice, CD4+ T cells comprise at least two functionally distinct cell types (TH1, TH2), distinguished on the basis of their lymphokine production. The balance between these subsets is critical for the outcome of an infection. In some rodent malarias, TH1 cells producing IFN-gamma and IL-2 are important for controlling infection in its early phases, while TH2 cells, producing i.a. IL-4 and IL-10, together with antibodies, are important for parasite clearance in later phases of infection. Distinct CD4+ T cells of either TH1 or TH2 type also have regulatory functions in human P. falciparum infection. In contrast to the CD4+ T cells, the role of CD8+ T cells in blood stage infection appears to be limited, but suppression of some CD4+ activities has been reported for both experimental and human malaria. As in other infections, peripheral T cells equipped with gamma/delta receptors are strongly upregulated in malaria and also respond to parasite antigens in vitro by proliferation and lymphokine production. However, the importance of the gamma/delta T cells for protection when compared with pathogenesis is presently unclear. Rapid advances made in recent years in the characterization and cloning of plasmodial antigens eliciting immune protection have made it possible to define some of the antigenic structures involved in T-cell immunity. This, together with an improved understanding of cellular mechanisms, provides some basis for the development of modern malaria vaccines.

Animals↗

PubMed1994

Lymphocyte responses to Plasmodium falciparum ring-infected erythrocyte surface antigen (Pf155/RESA) peptides in individuals with naturally acquired Plasmodium falciparum malaria.

Antibody titers and lymphocyte responses to synthetic peptides corresponding to repeated amino acid sequences of the 3' and 5' regions of Pf155/ring-infected erythrocyte surface antigen (RESA) were studied in two groups of Thai subjects, soldiers (Rangers), and villagers who differed in their history of malaria exposure. The frequency of Pf155/RESA seropositivity was similar in the two groups while the frequency of high titer antibody was significantly greater in villagers than in Rangers. Lymphocyte responsiveness in vitro to all Pf155/RESA peptides was infrequent for both groups although half of the subjects studied responded to crude Plasmodium falciparum asexual blood stage malaria antigen (MA). Among responders, Pf155/RESA peptides elicited lymphocyte responses in which proliferation and interferon-gamma (IFN-gamma) production were not associated, whereas with MA, the two responses were associated. The MA-stimulated lymphocyte proliferation and IFN-gamma production for both groups of volunteers appeared to be independent of antibody titer. In this study, antibody, but not lymphocyte, responses to Pf155/RESA peptides were shown to reflect differences in prior exposure and levels of acquired immunity to falciparum malaria.

Adult↗

PubMed1994

Characterization of regulatory T-cell responses in humans induced by the P. Falciparum blood stage antigen Pf155/RESA.

T-cells have a major role both as helper cells for efficient antibody production and as inducers and effector cells in antibody-independent malaria immunity. Thus, antigens to be included into a subunit vaccine must contain T-cell epitopes to become effectively immunogenic. The P. falciparum blood stage vaccine antigen Pf155/RESA has been shown to contain T-helper epitopes inducing T-dependent anti-malarial antibodies in vitro. We have also shown that synthetic peptides representing sequences from the amino-acid repeat regions of Pf155/RESA stimulate T-cells from P. falciparum primed donors to proliferate, to release IFN-gamma and/or IL-4. In individual donors there was no correlation between these different activities. Rather, they were frequently negatively associated. However, IL-4 secretion could be induced in T-cells from donors who had elevated concentrations of serum antibodies to the same peptide as used for T-cell activation. Taken together the results support the occurrence of malaria-specific CD4+ T-cell subsets (e.g. TH1 and TH2) in humans similar to what has been found in mice and suggest the involvement of TH2-type helper cells in the induction of some important P. falciparum specific antibodies. CD4+ T-cells recognize the antigen in the context of MHC class II molecules. However, in human outbred populations no consistent MHC restrictions of anti-Pf155/RESA immune responses could be demonstrated. This is not surprising in view of the extensive polymorphism of the HLA system. Neither were there any obvious MHC class II restrictions seen when antibody- and t-cell responses were measured in naturally primed monozygotic twins.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Th1/Th2 profiles in tuberculosis, based on the proliferation and cytokine response of blood lymphocytes to mycobacterial antigens.

Proliferation and cytokine production profiles by blood mononuclear cells in response to in vitro stimulation with mycobacterial antigens were compared in patients with active tuberculosis and in sensitized healthy controls. Interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) were detected at single-cell level using the ELISPOT assay. Patients showed significantly (P < 0.01) increased numbers of IL-4-secreting cells and decreased thymidine incorporation, but no significant difference in IFN-gamma-producing cells in response to the 38,000 MW or 19,000 MW antigens and their immunodominant peptide epitopes. Pronounced individual variations were found in both patient and control groups, when comparing the responsiveness to the mycobacterial extract, two protein antigens and five synthetic peptides. None of the antigens or peptides tested showed preferential stimulation of either IL-4- or IFN-gamma-secreting T cells, and proliferation was not correlated with either IL-4 or IFN-gamma production. In particular, cytokine responsiveness was of similar frequency in subjects who did or did not show positive proliferation, indicating that the latter test was not fully representative of the active T-cell repertoire. It is concluded that the demonstrated Th2 type of profile in response to two prominent mycobacterial antigens may play a role in the mechanisms of defective host resistance in tuberculosis.

Adolescent↗

PubMed1993

Number of interleukin-4- and interferon-gamma-secreting human T cells reactive with tetanus toxoid and the mycobacterial antigen PPD or phytohemagglutinin: distinct response profiles depending on the type of antigen used for activation.

The enzyme-linked immunospot (ELISPOT) assay has been proven to be an efficient and sensitive method for the enumeration of single cells secreting antibodies or cytokines. Here we have used this method to determine the number of interleukin-4 (IL-4)- and interferon-gamma (IFN-gamma)-producing cells in vitro secondary responses to tetanus toxoid (TT) and the mycobacterial antigen (purified protein derivative; PPD) or the mitogen phytohemagglutinin (PHA). PHA-induced IL-4 and IFN-gamma secretion was well correlated suggesting polyclonal activation of cells. This was not the case with the specific antigens, where PPD preferentially induced IFN-gamma- and very few IL-4-producing cells, while TT-induced both IL-4 and IFN-gamma. These differences are probably a reflection of the types of immunity the two antigens induce, mycobacteria preferentially inducing a cell-mediated T helper type 1 (Th 1) type of immunity, while immunity to tetanus is an antibody-dependent, Th 2 type of response. In individuals recently boosted with TT, a significant increase in both IL-4- and IFN-gamma-producing cells in response to TT was seen at day 7 after boost, followed by decline. This was in contrast to what was seen in response to PPD where an increase of IFN-gamma-producing cells after the TT boost at day 7 persisted for at least 14 days. These results suggest that after an in vivo boost both antigen-specific and nonspecific T cells are activated and that antigen-specific cells home to other organs and therefore may be difficult to demonstrate in the circulation. Our data show that the ELISPOT assay is a powerful tool for determining the frequency of cells secreting cytokines. The assay has several advantages over other assays since it is sensitive, measures the number of actually secreting cells, and avoids the problems of binding of cytokines to their cell-bound or soluble receptors.

Adult↗

PubMed1993

Anti-malarial antibodies in twins: reply.

Explore the source record for details and available documents.

Letter↗

PubMed1992

Genetic regulation of human anti-malarial antibodies in twins.

Immune responses to defined antigens may differ between individuals in a population as the reflection of differences in genetic regulation. In experimental animals, variation in responsiveness to a given epitope may be due to major histocompatibility complex (HLA, in humans) class II restrictions, implying serious limitations for the development of subunit vaccines. For human populations, knowledge of the relative importance of genetic as opposed to environmental factors affecting the immune response is scarce. We have compared antibody levels after immunization through repeated infections to a major malarial antigen (Pf155/RESA) in monozygotic twins with those in dizygotic twins, siblings, or unrelated controls. Antibody responses to the intact antigen and to some of its immunodominant epitopes were found to be more concordant within monozygotic twin pairs than in dizygotic pairs or age- and sex-matched siblings living under similar environmental conditions. The results support the conclusion that the antibody responses were genetically regulated. When the responses were assessed for possible associations with different HLA class II DRB, DQA, and DQB alleles had haplotypes, no associations were found. This suggests that the regulation of the Pf155/RESA antibody responses seen in this study reflects the impact of factors encoded by genes outside the HLA class II regions.

Adolescent↗

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↗

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↗