Immunogenicity of multiple antigen peptides containing B and non-repeat T cell epitopes of the circumsporozoite protein of Plasmodium falciparum.

We have characterized the immune response of mice to multiple Ag peptide systems (MAP) containing the immunodominant B cell epitope (NANP)3 and one of three distinct Th epitopes, Th2R, Th3R, and CS.T3, of the C terminal region of the circumsporozoite protein of Plasmodium falciparum, a human malaria parasite. Mice of three different MHC haplotypes (H-2k, H-2d, and H-2a) were immunized with the various MAP constructs. Mice of all three strains produced antibodies, but their anti-sporozoite titers were considerably lower than their anti-peptide titers as detected by ELISA. These antibodies reacted at high titers not only with the repeat polymer (NANP)50, but also with MAP that contained only the respective Th sequence. The antibody binding site within each of the Th sequences was mapped, using truncated peptides, in an inhibition assay. A primary antibody response, induced by a single i.v. inoculation of sporozoites, was greatly enhanced by the injection of MAP.

[Radioactive contamination of cistern waters along the Croatian coast of the Adriatic Sea]. / Radioaktivna kontaminacija cisternskih voda duz hrvatske obale Jadranskog mora.

Measurements of radioactive contamination of cistern waters with 90Sr, 134Cs and 137Cs have been carried out along the Croatian coast of the Adriatic Sea. An exponential decline of radioactivity followed the moratorium on nuclear tests. After the nuclear accident at Chernobyl, high radioactivity levels were detected again. The pre-Chernobyl and the post-Chernobyl mean residence times of 90Sr in cistern waters reflect the mechanism by which strontium was released to the atmosphere (atmospheric nuclear weapon tests conducted in the stratosphere or explosions in the Chernobyl nuclear reactor releasing radioactive material to the troposphere). For the pre-Chernobyl period, the mean residence time of 90Sr in cistern waters was similar to that calculated for fallout, being approximately 10 years. The post-Chernobyl 137Cs/90Sr activity ratio has been decreasing, but it has not yet reached the pre-Chernobyl values (approximately 1.6). The time-dependent 134Cs/137Cs activity ratio reflects the Chernobyl reactor inventory of these radionuclides. The annual dose for the critical adult population received from 90Sr, 134Cs and 137Cs by consumption of cistern water was estimated to be a few percentages of the dose from natural background radiation.

Prevalence and level of antibodies to the circumsporozoite proteins of human malaria parasites, including a variant of Plasmodium vivax, in the population of two epidemiologically distinct areas in the state of Acre, Brazil.

A seroepidemiological study of the prevalence of antibodies against the repeating epitopes of circumsporozoite (CS) proteins of human malaria parasites was conducted in 2 different areas in the state of Acre, Brazil in 1987 and 1990. In 1987 antibodies against the CS protein of the VK 247 variant Plasmodium vivax as well as antibodies against the CS proteins of P. falciparum and the classic P. vivax were found at relatively high rates in the 2 areas, but significant microepidemiological differences were observed. In 1990, when large scale migration in Amazonia had ceased and control measures were applied in the study areas, the malaria endemicity decreased, as determined by the declining prevalence of anti-sporozoite antibodies against all Plasmodium species, and the small number of individuals with positive blood smears. Antibodies against sporozoites of the variant P. vivax did not cross-react with the CS proteins of the classic P. vivax, nor with antibodies against sporozoites of P. falciparum and P. malariae. Sera containing antibodies against the CS protein of P. malariae were found at a very low frequency, and only in 1987. The anti-CS protein antibody response to all Plasmodium species was age-related.

Blood stage-induced Plasmodium brasilianum infection in the squirrel monkey induces antibodies which react with the circumsporozoite protein.

A blood stage-induced P. brasilianum infection in a naive squirrel monkey induced antibodies which reacted with the circumsporozoite protein of the parasite. Titers increased with duration of infection and persisted for 3 months after cure. In an immunoblot, these antibodies detected two polypeptides with molecular weights identical to those of the circumsporozoite protein and its precursor.

Widespread reactivity of human sera with a variant repeat of the circumsporozoite protein of Plasmodium vivax.

A panel of Brazilian and Indian sera was screened for reactivity with a variant strain of Plasmodium vivax recently isolated in Thailand. This strain has been shown to have a unique repeat region which differs from the previously described P. vivax CS proteins. A total of 21/343 human sera were found to react with a synthetic peptide representing the variant P. vivax repeat. All of the sera that reacted with the variant repeat peptide, (ANGAGNQPG)4, also reacted with variant P. vivax sporozoites. Both the anti-peptide and the antisporozoite reactivity were totally abolished by adsorption with the variant peptide. Some of the human sera contained variant antibodies that were species specific and could only be adsorbed with the specific variant peptide. These findings suggest that the variant strain of P. vivax might have a worldwide distribution. We also found that some of the variant positive sera reacted with P. brasilianum sporozoites and with the P. brasilianum/P. malariae CS repeat. The adsorption of these sera with the P. brasilianum/P. malariae repeat peptide, (NAAG)4, significantly reduced the reactivity of these sera with the P. vivax variant. In addition, polyclonal and monoclonal antibodies of mice immunized with P. brasilianum sporozoites cross-reacted with the variant P. vivax CS. These findings suggest that exposure to P. brasilianum or P. malariae may give rise to sporozoite antibodies which cross-react with the P. vivax variant CS.

Presence of a circumsporozoite-like protein in micronemes of blood-stage merozoites of malaria parasites.

We demonstrate for the first time the presence of a circumsporozoite (CS)-like protein in invasive blood stages of malaria parasites. Immunogold electron microscopy using antisporozoite monoclonal antibodies localized these antigens in the micronemes of merozoites. Western immunoblot and two-dimensional gel electrophoresis of mature blood-stage extracts of Plasmodium falciparum, P. berghei, P. cynomolgi, and P. brasilianum identified polypeptides having the same apparent molecular mass and isoelectric points as the corresponding sporozoite (CS) proteins. The CS-like protein of merozoites is present in relatively minor amounts, compared to the CS protein of sporozoites. Mice with long-term P. berghei blood-induced infections develop antibodies which react with sporozoites.

A circumsporozoite-like protein is present in micronemes of mature blood stages of malaria parasites.

We demonstrate for the first time the presence of a circumsporozoite (CS)-like protein in invasive blood stages of malaria parasites. Immunogold electron microscopy using antisporozoite monoclonal antibodies localized these antigens in the micronemes of merozoites. Western immunoblot and two-dimensional gel electrophoresis of mature blood stage extracts of Plasmodium falciparum, P. berghei, P. cynomolgi, and P. brasilianum identified polypeptides having the same apparent molecular mass and isoelectric points as the corresponding sporozoite (CS) proteins. The CS-like protein of merozoites is present in relatively minor amounts, compared to the CS protein of sporozoites. Mice with long-term P. berghei blood-induced infections develop antibodies which react with sporozoites.

Association of microneme antigens of Plasmodium brasilianum merozoites with knobs and other parasite-induced structures in host erythrocytes.

The localization of Plasmodium brasilianum antigens, common to merozoite micronemes and parasite-induced structures in the host erythrocyte, was determined by means of immunogold electron microscopy and monoclonal antibodies directed against blood stages of this parasite. All monoclonal antibodies reacted with micronemes. In addition, some reacted with either knob protrusions or caveolae of the host erythrocyte membrane; one reacted with a parasite-derived antigen present in the erythrocyte cytoplasm. Gold particles appeared over the membranes of ring-infected cells before the appearance of knobs and caveolae. We hypothesize that at least some knob- and caveolae-associated antigens of P. brasilianum are inserted into the erythrocyte membrane at the time of merozoite invasion.

Membrane-associated antigens of blood stages of Plasmodium, brasilianum, a quartan malaria parasite.

The localization of Plasmodium brasilianum-derived antigens in short and long clefts within the cytoplasm of infected erythrocytes and in association with knobs of the host cell membrane was demonstrated by immunoelectron microscopy with monoclonal antibodies. Our results document that malaria-induced short and long clefts, previously distinguishable only by morphology, differ also in antigenic composition. Another parasite-derived antigen was found to be associated with the parasitophorous vacuole space in schizonts. In segmenters, this antigen was present in large amounts between merozoites and in the cytoplasm of infected cells. These antigens were characterized by biosynthetic labeling and gel electrophoresis.

Potential vectors of malaria and their different susceptibility to Plasmodium falciparum and Plasmodium vivax in northern Brazil identified by immunoassay.

During the period from May 1983 to July 1985 we conducted an epidemiological study to determine potential vectors of malaria in 6 districts in the state of Pará in northern Brazil. The examination of random human blood smears, prepared at the time of mosquito capture, indicated overall human infection rates of 16.7% and 10.9% for Plasmodium falciparum and P. vivax, respectively. Two immunoassays, the immunoradiometric assay (IRMA) and the enzyme-linked immunosorbent assay (ELISA), based on the use of species-specific antisporozoite monoclonal antibodies, were used to analyze a total of 9,040 field-collected Anopheles mosquitoes for plasmodial infection. P. falciparum sporozoite antigen was detected in A. darlingi at rates varying from 2.7% to 4.2%, and in small numbers of A. oswaldoi collected in 1 of the districts. In contrast, sporozoite antigen of P. vivax was found in A. darlingi, A. triannulatus, A. nuneztovari, and A. albitarsis at rates ranging from 0.9% to 12.0%. By dissection, sporozoites were found in the salivary glands of these same 4 species at rates ranging from 0.8% to 2.2%. The latter 3 species had not previously been implicated as malaria vectors of any significance in northern Brazil.