LINEAR AND MULTIPLE ANTIGEN PEPTIDES CONTAINING DEFINED T-EPITOPE ANDB-EPITOPE OF THE PLASMODIUM-YOELII CIRCUMSPOROZOITE PROTEIN - ANTIBODY-MEDIATED PROTECTION AND BOOSTING BY SPOROZOITE INFECTION

We previously reported the identification of a T cell epitope in the N -terminal part of the circumsporozoite protein (CSP) of Plasmodium yoe lii yoelii (Pyy), CD4(+) T cell clones derived from mice immunized wit h a 21-mer peptide (amino acids 59-79, referred to as Py1) containing this epitope confer complete protection after passive transfer in mice , These clones proliferate in vitro in the presence of a 13-mer peptid e (amino acids 59-71, referred to as Py1T), This shorter peptide was f ound to behave as a T-h epitope in vivo, allowing overcoming of the ge netic restriction for production of anti-repeat antibodies in BALB/c m ice, when cross-linked to three (QGPGAP) repeats of the Pyy CSP, In th is study, we report protection in BALB/c mice, against a challenge wit h Pyy sporozoites after immunization with linear and multiple antigen peptides containing Py1T as T epitope and three repeats QGPGAP (Py3) a s B epitope, Multiple antigen peptide (MAP4-Py1T-Py3)-induced immunity was shown to be more effective than immunity induced by the linear fo rm of the conjugate (Py1T-Py3), protecting against challenges with hig her numbers of sporozoites, In both cases, levels of anti-repeat antib odies were strongly correlated with anti-parasite antibodies and prote ction, When tested in vitro, sera from mice immunized with the protect ive constructs strongly inhibited Pyy liver stages, while lymph node T cells displayed no cytotoxicity, In vivo, depletion of CD4(+) or CD8( +) T cells did not affect protection, Furthermore, MAP4-Py1T-Py3-immun ized mice were not protected against a challenge with P. yoelii nigeri ensis sporozoites, a parasite which has the same Py1T sequence but dif fers from Pyy in its repeated sequence, These results demonstrate that anti-repeat antibodies raised by immunization with the linear or the MAP form are exclusively responsible for the protection, Furthermore, this antibody response is boosted by a sporozoite challenge, allowing protection against a second challenge.