Identification of Id1-DBL2X of VAR2CSA as a key domain inducing highly inhibitory and cross-reactive antibodies.
OBJECTIVE
VAR2CSA is considered as the main target of protective immunity against pregnancy-associated malaria. VAR2CSA high molecular weight complicates scaling up production of VAR2CSA recombinant protein for large-scale vaccination programmes. We previously demonstrated that antibodies induced by NTS-DBL1X-Id1-DBL2X efficiently block parasite binding to CSA in a similar manner to antibodies induced by the full-length extracellular part of VAR2CSA. In order to identifying the shortest fragment of VAR2CSA carrying major protective epitopes able to elicit inhibitory antibodies, we performed a refined antigenic mapping of NTS-DBL1X-Id1-DBL2X through a DNA vaccination technique.


RESULTS
Five single or double domains constructs encoding NTS-DBL1X, NTS-DBL1X-Id1, Id1, Id1-DBL2X and DBL2X were made and used to immunize mice. The NTS-DBL1X, NTS-DBL1X-Id1, and Id1-DBL2X fragments all raised high titer immune response, as measured by ELISA. The DBL2X fragment raised a weaker antibody titer, and the Id1 construct failed to elicit antibody. Sera from mice immunized with NTS-DBL1X or DBL2X constructs failed to block infected erythrocytes binding to CSA, whereas sera from mice immunized with NTS-DBL1X-Id1 showed partial inhibitory activity, and the Id1-DBL2X fragment elicited antisera that totally abrogated infected erythrocytes adhesion to CSA. IgG purified from Id1-DBL2X antisera showed a similar inhibitory profile than Id1-DBL2X antisera. Anti-FCR3 anti-Id1-DBL2X antibodies also efficiently block the adhesion of erythrocytes infected by the HB3 parasite line to CSA. Id1-DBL2X antisera recognized the surface of field isolates from pregnant women, and inhibited CSA-binding of all 8 isolates tested, although to a variable level.


CONCLUSIONS
We raised high-titer antibodies against several parts of the protein, and identified Id1-DBL2X as the minimal VAR2CSA fragment inducing antibodies with CSA-binding inhibitory efficiency in the same range as the full-length extracellular part of VAR2CSA.
Université Paris Descartes, Sorbonne Paris Cité, 75006 Paris, France.
Bita
B
Bordbar
Nicaise
N
Tuikue-Ndam
Pascal
P
Bigey
Justin
J
Doritchamou
Daniel
D
Scherman
Philippe
P
Deloron
D000328:Adult; D000818:Animals; D057134:Antibodies, Neutralizing / Q000235:genetics / Q000276:immunology; D000913:Antibodies, Protozoan / Q000235:genetics / Q000276:immunology*; D000953:Antigens, Protozoan / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism / Q000469:parasitology; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000235:genetics / Q000276:immunology; D017780:Malaria Vaccines / Q000235:genetics / Q000276:immunology*; D016778:Malaria, Falciparum / Q000276:immunology / Q000469:parasitology / Q000517:prevention & control; D008297:Male; D051379:Mice; D010963:Plasmodium falciparum / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000276:immunology / Q000469:parasitology / Q000517:prevention & control; D017434:Protein Structure, Tertiary; D014611:Vaccination; D019444:Vaccines, DNA
D057134:Antibodies, Neutralizing; D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D007074:Immunoglobulin G; D017780:Malaria Vaccines; C512601:VAR2CSA protein, Plasmodium falciparum; D019444:Vaccines, DNA