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Biomedical subjects

R F Anders

Publications and source records attributed to R F Anders.

At least 73 records · Page 4Linked to original sources
PubMed1989

Class II restriction in mice to the malaria candidate vaccine ring infected erythrocyte surface antigen (RESA) as synthetic peptides or as expressed in recombinant vaccinia.

The immune response to three peptides corresponding to the repeat regions of the malaria candidate vaccine ring infected E surface Ag (RESA) were studied. Both antibody responses and lymphocyte stimulation in mice injected with these peptides without carrier were found to be restricted to certain MHC class II haplotypes. Mice bearing IAk were strong responders to all three peptides. Mice bearing IAd were strong responders only to the 3' repeat peptides, the octamer and tetramer. Mice bearing Is or Iq did not respond to any repeat peptides. Remarkably, the pattern of genetic restriction of the antibody response to the entire RESA as expressed in vaccinia indicated that there were no other epitopes besides the three repeats. Because only one class II haplotype (i.e., k) out of five tested responded strongly to this peptide and only two out of five (i.e., k and d) responded to the octamer or tetramer, it may be difficult to achieve a good immune response against RESA in most or all humans.

Animals↗
PubMed1989

Molecular karyotyping of the rodent malarias Plasmodium chabaudi, Plasmodium berghei and Plasmodium vinckei.

The molecular karyotypes of four isolates of Plasmodium chabaudi, three of the subspecies P. chabaudi adami and one P. chabaudi chabaudi, as well as P. berghei and P. vinckei were studied by means of pulsed field gradient (PFG) gel electrophoresis. Each species appears to have 14 chromosomes, ranging in size from approximately 730 kb to greater than 2000 kb. The three P. chabaudi adami isolates did not appear any more similar to each other than to the P. c. chabaudi isolate. The chromosome locations of genes for a heat shock protein (hsp) 70, ribosomal RNA (rRNA), the precursor to the major merozoite surface proteins, dihydrofolate reductase and P. falciparum antigen 352 as well as four cloned DNA markers and a telomere probe were determined. However, a number of probes representing cloned P. falciparum antigens failed to hybridize to P. chabaudi DNA. Hence genes for malaria antigens appear to be much more divergent than genes for housekeeping functions.

Animals↗
PubMed1989

A protective monoclonal antibody recognizes a linear epitope in the precursor to the major merozoite antigens of Plasmodium chabaudi adami.

The monoclonal antibody 5C10/66 was shown to afford strong protection in mice against fulminating Plasmodium chabaudi adami infection. This was remarkable, as immunity to this organism is regarded to be mainly T-cell mediated. This antibody identified a 250-kDa molecule in schizonts and an 83-kDa fragment in merozoites. A cDNA clone selected by 5C10/66 was the homologue of the Plasmodium falciparum precursor to the major merozoite surface antigen (PMMSA). Comparison with the P. falciparum sequence showed that the P. chabaudi adami clone encoded the middle portion of the gene and that it can also be divided into variable and conserved blocks. Screening of a set of all possible octamer peptides predicted by the cDNA clone revealed that the core epitope of 5C10/66 was Glu-Thr-Thr-Glu-Thr. This region resides in a variable block of PMMSA.

Amino Acid Sequence↗
PubMed1989

Integral membrane protein located in the apical complex of Plasmodium falciparum.

We describe the cloning of a novel antigen of Plasmodium falciparum which contains a hydrophobic domain typical of an integral membrane protein. This antigen is designated apical membrane antigen 1 because it appears to be located in the apical complex. Apical membrane antigen 1 appears to be transported to the merozoite surface near the time of schizont rupture.

Amino Acid Sequence↗
PubMed1989

Small area variation in prevalence of an S-antigen serotype of Plasmodium falciparum in villages of Madang, Papua New Guinea.

Cross-sectional and longitudinal village-based studies of the transmission dynamics of an S-antigen serotype of the asexual erythrocyte stages of Plasmodium falciparum have been carried out in Madang, Papua New Guinea (PNG). Sera collected from village residents were screened for circulating S-antigen of the FC27 serotype by enzyme-linked immunosorbent assay (ELISA). The prevalence of the FC27 S-antigen was found to vary between villages at a given point in time, as well as within a village over time. Residents of villages 2-5 km apart were infected with P. falciparum of different S-antigen serotypes. This study documents the periodic nature of transmission of a sub-population of P. falciparum defined by the FC27 S-antigen. The variation in a small area in the prevalence of this serotype of P. falciparum in Madang illustrates the complexities of malaria transmission which must be considered in the design of malaria vaccine trials.

Animals↗
PubMed1988

New approaches to the serotypic analysis of the epidemiology of Plasmodium falciparum.

Considerable antigenic heterogeneity of Plasmodium falciparum has been demonstrated in natural parasite populations. However, very little is known about the relative virulence, transmission efficiency and prevalence over space and time of parasites expressing different serotypes of variant antigens. The recent application of recombinant DNA techniques to express a wide range of P. falciparum antigens in Escherichia coli has led to a better understanding of the molecular basis of antigenic diversity of a number of parasite proteins including the precursor to the major merozoite surface antigen (PMMSA) and the heat-stable S-antigens. Highly specific reagents such as DNA probes, monoclonal antibodies and polyclonal antisera to either cloned antigens or synthetic peptides have become available for serotypic analysis of natural parasite populations. With these reagents important epidemiological questions can now be asked concerning the population biology of different serotypes of P. falciparum. The use of the polymorphic S-antigen system as a serotypic marker to analyse the transmission dynamics of P. falciparum in Madang, Papua New Guinea (PNG) is discussed. Results of serotyping studies with the S-antigen system highlight the complexities of malaria transmission, which require consideration in the design of malaria vaccine trials.

Animals↗
PubMed1988

Variation in the precursor to the major merozoite surface antigens of Plasmodium falciparum.

The major antigens on the surface of Plasmodium falciparum merozoites are derived from a single high molecular weight polypeptide. The precursor to the major merozoite surface antigen (PMMSA) has conserved and variable antigenic determinants and varies in size in different isolates. Since the protein is a candidate for a malaria vaccine, it is important to understand the molecular basis of this variation. We present the complete sequence of the PMMSA of the Papua New Guinea isolate FC27 and the partial sequence of the West African isolate NF7. The gene consists of blocks of sequence which are either conserved or variable between different isolates. Variable sequences fall into two distinct types, indicating that the PMMSA is encoded by dimorphic alleles that undergo recombination within conserved blocks at the 5' end of the gene. Genetic exchange is not apparent within the other two-thirds of the gene in 12 isolates, suggesting strong selection against such recombinants. The most variable block located near the 5' end contains repeats that are different in independent cloned isolates. This variation presumably accounts for much of the size and antigenic variability.

Alleles↗
PubMed1988

A component of an antigenic rhoptry complex of Plasmodium falciparum is modified after merozoite invasion.

Human antibodies affinity purified on an adsorbent prepared from a cDNA clone (Ag44) expressing a portion of a rhoptry antigen were used to characterize the synthesis and fate of the antigen in the asexual blood stages of Plasmodium falciparum. The rhoptry antigen is synthesized in the mature trophozoite-stage parasites as a 103 kDa polypeptide, is present in the schizonts and merozoites as a 105 kDa polypeptide, is discharged from the rhoptries and found in the newly invaded red cells as a 110 kDa polypeptide. Anti-Ag44 antibodies immunoprecipitate the antigen and two additional polypeptides of 135 and 150 kDa from lysates of infected cells and from culture supernatants. The three polypeptides are associated in a non-covalent complex that persists in the newly invaded red cells. All the components of the high molecular weight rhoptry complex are antigenic and can be precipitated with immune human serum. The 135 kDa polypeptide is identical to a 140 kDa rhoptry antigen previously identified by a monoclonal antibody.

Animals↗
PubMed1988

MESA is a Plasmodium falciparum phosphoprotein associated with the erythrocyte membrane skeleton.

The mature-parasite-infected erythrocyte surface antigen (MESA) of Plasmodium falciparum is an antigenically variable, high molecular weight protein of trophozoites and schizonts that is located at the erythrocyte surface membrane. It is first synthesized at the late ring stage and continues to be synthesized until late schizogony. MESA cannot be detected on the external surface of erythrocytes infected by trophozoites and early schizonts but is located at the internal surface in association with the erythrocyte membrane skeleton. The degree of association with the membrane skeleton varies among parasite lines, being greater in knobby parasite lines. MESA is phosphorylated and is present in a similar location to another phosphoprotein, the ring-infected erythrocyte surface antigen (RESA). However, it differs from RESA in being detected at a later stage of asexual development of the parasite.

Animals↗
PubMed1988

Identification of two integral membrane proteins of Plasmodium falciparum.

We describe the isolation and cloning of two integral membrane protein antigens of Plasmodium falciparum. The antigens were isolated by Triton X-114 temperature-dependent phase separation, electrophoretically transferred to nitrocellulose, and used to affinity-purify monospecific human antibodies. These antibodies were used to isolate the corresponding cDNA clones from a phage lambda gt11-Amp3 cDNA expression library. Clone Ag512 corresponds to a Mr 55,000 merozoite rhoptry antigen, and clone Ag513 corresponds to a Mr 45,000 merozoite surface antigen. Both proteins can be biosynthetically labeled with [3H]glucosamine and [3H]myristic acid, suggesting that they may be anchored in membranes via a glycosylphosphatidylinositol moiety. Similarities in the C-terminal sequences of the Mr 45,000 merozoite surface antigen and the Trypanosoma brucei variant surface glycoproteins provides further evidence that this antigen has a glycosylphosphatidylinositol anchor.

Amino Acid Sequence↗
PubMed1988

A second antigenic heat shock protein of Plasmodium falciparum.

We describe here an antigen of Plasmodium falciparum, defined by a cDNA clone designated Ag361. The antigen is a soluble cytoplasmic 70-kD polypeptide present in all isolates analyzed and in all stages of asexual development in the blood. The antigen is a natural immunogen, although it lacks repeating epitopes of many P. falciparum antigens. Ag361 shares extensive sequence homology with the hsp70 proteins of Xenopus laevis, Drosophila melanogaster, Escherichia coli, and man, as well as a previously isolated P. falciparum hsp70 protein. The genome of P. falciparum contains at least five hsp70-like genes, located on at lest four different chromosomes.

Amino Acid Sequence↗
PubMed1988

Patterns of antigen expression in asexual blood stages and gametocytes of Plasmodium falciparum.

The stage specificity and localization of 12 Plasmodium falciparum antigens were determined by immunofluorescence using acetone-fixed parasites reacted with monospecific antibodies against cloned antigens. Antibodies were prepared by immunization of rabbits with recombinant proteins or by affinity purification of human plasma against cloned antigen adsorbents. Most of the antigens occurred predominantly in mature asexual parasites, two were abundant in ring stages and three were absent in rings. Four of the 12 antigens were detected in asexual stages but not in gametocytes. Grouping of antigens by localization within blood stages was difficult because of the complexity of fluorescence patterns observed. With some antibodies, fluorescence was apparently distributed evenly over the parasites, but in other cases label was concentrated within discrete compartments or organelles. Extraparasitic intraerythrocytic fluorescence was also observed.

Animals↗
PubMed1988

Immunization trials with the ring-infected erythrocyte surface antigen of Plasmodium falciparum in owl monkeys (Aotus vociferans).

A protocol was developed for the testing of blood stage vaccines against Plasmodium falciparum using Peruvian Aotus vociferans and the Indochina I/CDC strain of the parasite. Three different fused polypeptide vaccines containing elements of the ring-infected erythrocyte surface antigen molecule combined with Freund's complete and Freund's incomplete adjuvants were tested to determine their ability to protect against overwhelming infection following challenge with this highly virulent strain of P. falciparum, and to invoke antibody responses as measured by a standard indirect immunofluorescence technique. Nine of 14 immunized animals exhibited some protection. Presented are the test procedures developed for the conduct of such trials with New World monkeys and the analysis of results that led to the identification of variables selected for study in future trials.

Animals↗