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Infect Immun, July 1998, p. 3232-3241, Vol. 66, No. 7
International Centre for Genetic Engineering
and Biotechnology, Aruna Asaf Ali Marg, New Delhi 110067, India
Received 17 November 1997/Returned for modification 15 December
1997/Accepted 14 April 1998
A cysteine-containing peptide motif, EWSPCSVTCG, is found highly
conserved in the circumsporozoite protein (CSP) and the
thrombospondin-related anonymous protein (TRAP) of all the
Plasmodium species analyzed so far and has been shown to be
crucially involved in the sporozoite invasion of hepatocytes. We have
recently shown that peptide sequences containing this motif, and also
the antibodies raised against the motif, inhibit the merozoite invasion
of erythrocytes. However, during natural infection, and upon
immunization with recombinant CSP, this motif represents a cryptic
epitope. Here we present the results of immunization studies with two
linear multiepitopic constructs, a 60-residue (P60) and a 32-residue
(P32) peptide, containing the conserved motif sequence. Both the
peptides per se generated high levels of specific antibodies in BALB/c
mice. P32 was found to be genetically restricted to
H-2d and H-2b
haplotypes of mice, whereas P60 was found to be immunogenic in five
different strains of mice. The antibody response was predominantly targeted to the otherwise cryptic, conserved motif sequence in P60.
Anti-P60 antibodies specifically stained the asexual blood stages of
Plasmodium falciparum and Plasmodium yoelii in
an immunofluorescence assay, recognized a 60- to 65-kDa parasite
protein in an immunoblot assay, and blocked P. falciparum
merozoite invasion of erythrocytes in a dose-dependent manner.
Immunization with P60 also induced significant levels of the cytokines
interleukin-2 (IL-2), IL-4, and gamma interferon in BALB/c mice.
Moreover, >60% of mice immunized with P60 survived a heterologous
challenge infection with a lethal strain of P. yoelii.
These results indicate that appropriate medium-sized synthetic peptides
might prove useful in generating specific immune responses to an
otherwise cryptic but critical and putatively protective epitope in an
antigen and could form part of a multicomponent malaria vaccine.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Induction of Protective Immune Responses by
Immunization with Linear Multiepitope Peptides Based on Conserved
Sequences from Plasmodium falciparum Antigens
*
Corresponding author. Mailing address: International
Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, P.O. Box 10504, New Delhi 110067, India. Phone: 00 91 11 6195007. Fax:
00 91 11 6162316. E-mail: virendra{at}icgebnd.ernet.in.
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