title: Plasmodium falciparum: characterization of toxin-associated proteins and identification of a hemoglobin containing parasite cytokine stimulator.
abstract: Previous studies have indicated the inositol monophosphate (IMP) is a component of the malaria parasite toxin that induces cytokines such as tumour necrosis factor (TNF). To further characterize the toxin we have labeled Plasmodium falciparum in vitro cultures with [14C]inositol or [35S]-methionine and immunoprecipitated the labeled antigens with an antiserum against IMP which blocks malaria parasite-induced TNF production. We detected four proteins associated with IMP when the immunoprecipitates were separated by SDS-PAGE and analyzed by autoradiography. To evaluate the capacity of different P. falciparum antigens to induce cytokine production we separated a mixture of exoantigens by SDS-PAGE gels. Antigen fractions of 43-71 kDa and of a low molecular mass of <20 kDa contained the dominant inducers of TNF alpha interleukin 1 alpha, and interleukin 6 production from human mononuclear cells. The low-molecular-mass antigen fraction contained hemoglobin, while no parasite-specific proteins were detectable when tested by immunoblotting. Hemoglobin may act as a carrier for cytokine-inducing malaria parasite toxins.
authors.affiliation: Centre for Medical Parasitology, University of Copenhagen, Denmark.
authors.forename: G
authors.initials: G
authors.lastname: Kristensen
authors.forename: P H
authors.initials: PH
authors.lastname: Jakobsen
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000032:analysis / Q000737:chemistry / Q000276:immunology; D001345:Autoradiography; D016207:Cytokines / Q000096:biosynthesis*; D004591:Electrophoresis, Polyacrylamide Gel; D006454:Hemoglobins / Q000032:analysis*; D007106:Immune Sera / Q000276:immunology; D015151:Immunoblotting; D051379:Mice; D010963:Plasmodium falciparum / Q000276:immunology*; D011233:Precipitin Tests; D015800:Protozoan Proteins / Q000032:analysis / Q000737:chemistry / Q000276:immunology*; D014118:Toxins, Biological / Q000032:analysis / Q000737:chemistry / Q000276:immunology*
chemical_list: D000953:Antigens, Protozoan; D016207:Cytokines; D006454:Hemoglobins; D007106:Immune Sera; D015800:Protozoan Proteins; D014118:Toxins, Biological