Drug-induced death of the asexual blood stages of Plasmodium falciparum occurs without typical signs of apoptosis.

There is clear evidence that most antimalarial drugs, while acting through different mechanisms, are associated with parasite growth/development inhibition and eventual parasite death. However, the exact mode of parasite death remains unclear. In the present study, we investigated the ability of various drugs, including two antimalarial drugs (chloroquine and atovaquone), a topoisemerase II inhibitor (etoposide) and a nitric oxide donor (S-nitro-N-acetyl-D, L-penicillamine), to induce apoptosis in a laboratory strain of Plasmodium falciparum.

Cytokine mRNA expression and iron status in children living in a malaria endemic area.

Iron deficiency has been reported to affect both malaria pathogenesis and cell-mediated immune responses; however, it is unclear whether the protection afforded by iron deficiency is mediated through direct effects on the parasite, through immune effector functions or through both. We have determined cytokine mRNA expression levels in 59 children living in a malaria endemic area on the coast of Kenya who we selected on the basis of their biochemical iron status. Real-time quantitative reverse transcriptase polymerase chain reaction analysis of cytokine mRNA levels of peripheral blood mononuclear cells (PBMC) obtained from these children showed an association between interleukin-4 (IL-4) mRNA levels and all the biochemical indices of iron that we measured.

IL4-589C/T polymorphism and IgE levels in severe malaria.

Previous studies identified an allelic variant of the IL4 promoter region (IL4-589T) that appears to enhance the transcriptional activity of IL4, and is associated with increased IgE levels. Total serum IgE levels are elevated in malaria endemic regions, and higher in children with severe malaria. Here, we investigated the relationship of the IL4-589C/T polymorphism with severity of the disease in a case-control study of severe malaria in Burkina Faso, West Africa.

IgE antibodies to Plasmodium falciparum and severity of malaria in children of one ethnic group living in Burkina Faso.

Plasmodium falciparum malaria infection induces elevated blood levels of both total immunoglobulin and anti-plasmodial antibodies belonging to different isotypes. We have previously shown that donors living in areas of malaria transmission develop malaria-specific IgE antibodies that are present at highest concentrations in patients with severe disease, suggesting a role for this isotype in malaria pathogenesis. To establish the possible importance of IgE in the course and severity of this disease, we have analyzed a large and homogenous group of African children (age range = 6 months to 15 years) belonging to one ethnic group (Mossi) living in identical epidemiologic conditions in the same urban area (Ougadougo) of Burkina Faso.

Immunoglobulin E (IgE) containing complexes induce IL-4 production in human basophils: effect on Th1-Th2 balance in malaria.

Human basophils are potent producers of IL-4 following cross-linking of the high affinity receptor for IgE (Fc epsilon R1). Elevated levels of both total- and malaria-specific IgE have been demonstrated in sera from people living in malaria-endemic regions. Whether or not these IgE antibodies are pathogenic is unclear.

Malaria research: host-parasite interactions and new developments in chemotherapy, immunology and vaccinology.

Malaria remains the major parasitic disease, with 300-500 million new infections each year. This survey covers recent advances in the field of parasite-host interactions, focusing on Plasmodium falciparum, the most virulent of the human parasites. Rapid progress in genomic research is creating a basis for the development of new drugs and vaccines.

IgE deposition in brain microvessels and on parasitized erythrocytes from cerebral malaria patients.

Postmortem brain tissues of 21 cerebral malaria cases were obtained in Myanmar and Vietnam. The tissues were examined by light microscopy and by an immunohistochemical method. Brain microvessels (capillaries and venules) were examined for the presence of immunoglobulins IgE and IgG, Plasmodium falciparum antigen, and parasitized erythrocytes (PRBC).

Malaria blood-stage infection and its control by the immune system.

Malaria is caused by the protozoon Plasmodium, transmitted to humans by Anopheles mosquitoes. The most dangerous of the plasmodia infecting humans is Plasmodium falciparum. The disease is caused by those parasite stages which multiply asexually in red blood cells.

A preliminary analysis of Wuchereria bancrofti microfilarial antigens for potential use in diagnosis.

Several antigens from the microfilarial stage of Wuchereria bancrofti have been identified using immunoblots of microfilarial antigens and screening with immune sera and tropical pulmonary eosinophilia (TPE) sera. This analysis revealed an array of antigens with apparent molecular weights of 14kDa, 35kDa, 42kDa, 63kDa, 88kDa, 97kDa and 200kDa. Among these only the 14kDa and 42kDa antigens were consistently recognized by most of the immune sera.

Contrasting functions of IgG and IgE antimalarial antibodies in uncomplicated and severe Plasmodium falciparum malaria.

Plasmodial infection results in a significant elevation of the blood concentrations of immunoglobulins including IgE. Two well-characterized groups of adult Thai patients with either uncomplicated or severe Plasmodium falciparum malaria were studied over a period of four weeks. The mean parasitemias were approximately three-fold higher in patients with severe malaria than in those with uncomplicated disease.

Immune regulation of protection and pathogenesis in Plasmodium falciparum malaria.

The immune mechanisms whereby malaria parasites are eliminated by the human host or how they may avoid the immune response are poorly understood. Individuals living in malaria-endemic areas gradually acquire immunity. It is well established that this immunity involves both cell-mediated and humoral mechanisms and that T cells are the major regulators in both these events.

Human immune responses to the highly repetitive Plasmodium falciparum antigen Pf332.

The B and T cell responses to EB200, a repetitive part of the Plasmodium falciparum antigen Pf332, were examined in malaria-exposed Senegalese adults. Most donors had high levels of antibodies to recombinant EB200 and 17 overlapping peptides spanning EB200. Taking proliferation and/or cytokine (interferon-gamma and interleukin-4) production as a measure of T cell activation, eight of the EB200-derived peptides induced responses in > 40% of the donors tested.

Antibodies to a non-repeat region of Plasmodium falciparum antigen Pf155/RESA in individuals from malaria-endemic areas.

Human antibodies to the repeat regions of the Plasmodium falciparum asexual blood stage antigen Pf155/RESA interfere with parasite growth in vitro, but the significance in this respect of antibodies to non-repetitive epitopes is less clear. In this study the levels of antibodies to a non-repetitive part of Pf155/RESA (residue 199-221) in malaria-exposed individuals were analysed, as was the parasite-inhibitory capacity of such antibodies. Residue 199-221 is of particular interest since it includes a sequence homologous to a cytoadherence-related motif from band 3.

Inhibition of in vitro growth of plasmodium falciparum field isolates mediated by human antibodies to Pf155/RESA and Pf332.

The capacity of antibodies to interfere with Plasmodium falciparum growth in in vitro cultures is considered to reflect some of their potential protective effects in vivo. Almost all previous analyses of antibody mediated inhibition of parasite growth in vitro were performed with different laboratory strains of P. falciparum.

Characterization of antibody responses to a Plasmodium falciparum blood-stage antigen induced by a DNA prime/protein boost immunization protocol.

The humoral immune responses elicited by priming with a DNA plasmid and boosting with either the plasmid or the corresponding recombinant protein in alum adjuvant were compared. The plasmid DNA encoded a sequence (M3) derived from the Plasmodium falciparum antigen Pf155/RESA, and the recombinant protein consisted of the identical malarial sequence fused to an albumin-binding region (BB) of streptococcal protein G. Mice of different genetic backgrounds (CBA, Balb/c and C57Bl/6) were primed with plasmid DNA and boosted with either plasmid or recombinant protein.

IgE and tumor necrosis factor in malaria infection.

IgE, the immunoglobulin instrumental in atopic diseases is also elevated in many infections. This paper reports on the occurrence and possible pathogenic role of IgE in human Plasmodium falciparum malaria, one of the most widely spread and severe infectious diseases world wide. Plasmodial infections induce IgE elevation in the blood of the majority of people living in malaria endemic areas and up to 5% of this IgE constitutes anti-malaria antibodies.

Selected problems of malaria blood stage immunity.

Both antibody dependent and cell mediated mechanisms contribute to immunity in malaria. The parasites vary in sensitivity to antibody mediated inhibition due to underlying antigenic variation. When Plasmodium falciparum isolates are tested with antibodies from the donor originally harbouring the parasites or with those from other donors, growth inhibition is usually lowest in the autologous combinations.

Antibodies to sequences in a non-repeat region of Plasmodium falciparum antigen Pf155/RESA inhibit either cytoadherence or parasite growth in vitro.

Antibodies to a non-repeat region of the Plasmodium falciparum antigen Pf155/RESA were investigated for their capacity to inhibit parasite cytoadherence to melanoma cells and parasite growth in vitro. The activities of these antibodies were studied since the target region in Pf155/RESA includes a cytoadherence-related motif also found in loop 3 and 7 of human erythrocyte band 3 protein. Overlapping multiple antigen peptides (MAPs) together spanning residues 199-220 of Pf155/RESA were used to raise antibodies in rabbits.

Antibodies to nonrepeat sequences of antigen Pf155/RESA of Plasmodium falciparum inhibit parasite growth in vitro.

Immune responses to the repeat regions of the Plasmodium falciparum antigen Pf155/RESA have been extensively studied, and antibodies to the repeats are known to interfere with parasite growth both in vitro and in vivo. Less is known with regard to the effect on parasites of antibodies to the nonrepeat regions of the antigen. In the present study, rabbits were immunized with synthetic peptides corresponding to three different nonrepeated sequences of antigen Pf155/RESA.

Differential induction of immunoglobulin G subclasses by immunization with DNA vectors containing or lacking a signal sequence.

The route and method used to immunize mice with antigen-expressing DNA plasmids have an impact on the resulting T-helper cell response and IgG subclass distribution. Previous findings further indicate that the intracellular targeting of expressed antigens influences the differentiation of naive T-cells into either a Th1 or a Th2 type of response. In the present study, we analyzed the levels of IgG1 and IgG2a antibodies, as correlates of Th2 and Th1 responses, respectively, after intramuscular injection of mice with plasmids encoding a chimeric protein containing a Plasmodium falciparum blood stage antigen expressed in two different forms.

Immunogenicity of chimeric multiple antigen peptides based on Plasmodium falciparum antigens: impact of epitope orientation.

Assembly of B and T epitopes in multiple antigen peptides (MAP) can bypass genetically predisposed unresponsiveness to B epitopes. Although the underlying mechanisms are unknown, B-cell responses to such diepitope MAP are influenced by intramolecular epitope orientation. In this study, MAP constructs were synthesized, encompassing two epitopes derived from the Plasmodium falciparum antigens circumsporozoite protein (CS) and Pf332.

A malariometric survey in a rural community in the Muheza district, Tanzania: age profiles in the development of humoral immune responses.

A malariometric survey was carried out in a rural community situated in a malaria holoendemic endemic area of Tanzania. A random sample (n = 228) of different age groups was taken to elucidate the association between anti-Pf155/RESA and anti-Pf332 antibody responses and classical malaria indices. Parasitaemia, fever, splenomegaly, haematocrit and antimalarial consumption were assessed.

T- and B-cell responses of malaria immune individuals to synthetic peptides corresponding to non-repeat sequences in the N-terminal region of the Plasmodium falciparum antigen Pf155/RESA.

While the C-terminal repeat region of Pf155/RESA, a Plasmodium falciparum vaccine candidate has been extensively studied for B- and T-cell reactivities, little is so far known about the non-repeat region in this respect. The present study aimed at investigating the non-repeat sequence 171-227 of Pf155/RESA for T- and B-cell epitopes. Eight overlapping peptides were synthesised and assayed for their ability to stimulate peripheral blood mononuclear cells obtained from P.

Comparative study of DNA-based immunization vectors: effect of secretion signals on the antibody responses in mice.

The presence of a signal sequence preceding the gene encoding a target antigen in a DNA vaccine should facilitate secretion of the in vivo translated antigen. The immune responses elicited upon injection with such a vector could differ from those induced by the same vector lacking a signal sequence. In the present study, the humoral responses elicited in mice immunized with two plasmids, either containing or lacking the human tissue plasminogen activator signal sequence, were compared.