Expression of Plasmodium falciparum erythrocyte membrane protein 1 in experimentally infected humans.
BACKGROUND
Parasites causing severe malaria in non-immune patients express a restricted subset of variant surface antigens (VSA), which are better recognized by immune sera than VSA expressed during non-severe disease in semi-immune individuals. The most prominent VSA are the var gene-encoded Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family, which is expressed on the surface of infected erythrocytes where it mediates binding to endothelial receptors. Thus, severe malaria may be caused by parasites expressing PfEMP1 variants that afford parasites optimal sequestration in immunologically naive individuals and high effective multiplication rates.


METHODS
var gene transcription was analysed using real time PCR and PfEMP1 expression by western blots as well as immune plasma recognition of parasite cultures established from non-immune volunteers shortly after infection with NF54 sporozoites.


RESULTS
In cultures representing the first generation of parasites after hepatic release, all var genes were transcribed, but Group A var genes were transcribed at the lowest levels. In cultures established from second or third generation blood stage parasites of volunteers with high in vivo parasite multiplication rates, the var gene transcription pattern differed markedly from the transcription pattern of the cultures representing first generation parasites. This indicated that parasites expressing specific var genes, mainly belonging to group A and B, had expanded more effectively in vivo compared to parasites expressing other var genes. The differential expression of PfEMP1 was confirmed at the protein level by immunoblot analysis. In addition, serological typing showed that immune sera more often recognized second and third generation parasites than first generation parasites.


CONCLUSIONS
In conclusion, the results presented here support the hypothesis that parasites causing severe malaria express a subset of PfEMP1, which bestows high parasite growth rates in individuals with limited pre-existing immunity.
Lavstsen
Thomas
T
Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, Blegdamsvej 3, 2200 Copenhagen N, Denmark. thomaslavstsen@vip.cybercity.dk
Magistrado
Pamela
P
Hermsen
Cornelus C
CC
Salanti
Ali
A
Jensen
Anja T R
AT
Sauerwein
Robert
R
Hviid
Lars
L
Theander
Thor G
TG
Staalsoe
Trine
T
D000818:Animals; D000954:Antigens, Surface / Q000096:biosynthesis / Q000276:immunology; D015153:Blotting, Western / Q000379:methods; D002460:Cell Line; D005434:Flow Cytometry / Q000379:methods; D015870:Gene Expression / Q000502:physiology*; D020869:Gene Expression Profiling / Q000379:methods / Q000662:veterinary; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D016778:Malaria, Falciparum / Q000276:immunology* / Q000469:parasitology; D018512:Parasitemia / Q000097:blood; D010963:Plasmodium falciparum / Q000276:immunology / Q000502:physiology; D016133:Polymerase Chain Reaction / Q000379:methods; D015800:Protozoan Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology*; D012100:Reproduction, Asexual / Q000502:physiology; D013997:Time Factors; D014158:Transcription, Genetic / Q000235:genetics / Q000502:physiology
D000954:Antigens, Surface; D007074:Immunoglobulin G; D015800:Protozoan Proteins; C085731:erythrocyte membrane protein 1, Plasmodium falciparum