Passive transfer of Plasmodium falciparum MSP-2 pseudopeptide-induced antibodies efficiently controlled parasitemia in Plasmodium berghei-infected mice Paola A. Martı ´nez a , Nubia Yandar a , Liliana P. Lesmes a , Martha Forero a , Oscar Pe ´ rez-Leal a , Manuel Elkin Patarroyo a,b , Jose ´ Manuel Lozano a,b,c, * a Fundacio ´n Instituto de Inmunologı´a de Colombia-FIDIC, Bogota ´, Colombia b Departamento de Farmacia and Facultad de Medicina, Universidad Nacional de Colombia, Bogota ´, Colombia c Facultad de Medicina, Universidad Colegio Mayor de Nuestra Sen ˜ora del Rosario, Bogota ´, Colombia 1. Introduction Merozoite surface proteins (MSP) have been considered as potential vaccine candidates against Plasmodium spp. blood-stages due to their easy accessibility which turns them into excellent immune system’s targets [40]. Among these surface proteins interacting with erythrocyte membrane during invasion, the MSP- 2 has gained notable attention as a source of vaccine candidate peptides, since the reactivity of antibodies acquired by humans duringnaturalinfection againstthisprotein isassociated withclinical immunity against malaria [40]. The MSP-2 is a 35–56 kDa glycoprotein whose size and isoelectric point vary depending on the parasite strain. Itisdisplayedoverthe surface ofmerozoites and in residual bodies from all Plasmodium falciparum strains studied so far [6,45]. It possess a highly polymorphic central region flanked by dimorphicsequences of either ICI or FC27 allelic families, which are in turnflankedby conserved sequences [13,46,50] asobservedin Fig.1A. The isotype of antibodies produced in response to P. falciparum MSP-2 during infection generally reflects the type of parasite allele causing the infection and the length of exposure [36,49,52]. Some studies have shown that monoclonal antibodies directed against MSP-1 and MSP-2 surface antigens inhibit in vitro parasite growth [10,25,39], while others have established that immunizing mice with peptides from the P. falciparum MSP-2 N-terminal region makes them capable of protecting themselves against P. berghei and P. yoelii strains [24,43]. It has been reported that a MSP-2 N-terminal region peptide (namely 4044) bound with high specificity to human erythrocytes and possesses three binding motifs [34]. Bearing in mind that humoral immunity plays an important role in the defense against blood-stage infections [3–5,11,14,27,30,37,41,44], passive immunization is considered to be a potential strategy in the search for epitopes and in studying the mechanisms by which antibodies provide a protective effect against a pathogen-causing disease. Steric interference in merozoite invasion of erythrocytes, inhibition of intra-erythrocyte development or processing of merozoite surface proteins, antibody-depend cell inhibition and phagocytosis are among the mechanisms proposed to date for explaining how antibodies achieve their effect [9,28,39,54,55]. Studies on mice have shown that passive immunization with antibodies directed against P. yoelii AMA-1, CS, MSP-1, proteins confer protection [31,32,47]. It has been demonstrated in vitro that IgG antibodies from African adults immune to P. falciparum have inhibited parasite growth in cooperation with monocytes; which was correlated with reduced in vivo parasitemia [3]. Peptides 30 (2009) 330–342 ARTICLE INFO Article history: Received 9 September 2008 Received in revised form 24 October 2008 Accepted 27 October 2008 Available online 21 November 2008 Keywords: Pseudopeptide Ig isotype Murine malarial infection In vivo neutralizing activity Anti-malarial vaccine ABSTRACT We have developed monoclonal antibodies directed against the pseudopeptide c-130, derived from the highly conserved malarial antigen Plasmodium falciparum merozoite surface protein 2 (MSP-2), for obtaining novel molecular tools with potential applications in the control of malaria. Following isotype switching, these antibodies were tested for their ability to suppress blood-stage parasitemia through passive immunization in malaria-infected mice. Some proved totally effective in suppressing a lethal blood-stage challenge infection and others reduced malarial parasitemia. Protection against P. berghei malaria following Ig passive immunization can be associated with specific immunoglobulins induced by a site-directed designed MSP-2 reduced amide pseudopeptide. ß 2008 Elsevier Inc. All rights reserved. * Corresponding author at: Fundacio ´ n Instituto de Inmunologı ´a de Colombia- FIDIC, Carrera 50 No. 26-00, ZC 020304, Bogota ´ , Colombia. Tel.: +57 1 315 8920; fax: +57 1 481 5269. E-mail addresses: jm_lozano@fidic.org.co, jmlozanom@unal.edu.co (J.M. Lozano). Contents lists available at ScienceDirect Peptides journal homepage: www.elsevier.com/locate/peptides 0196-9781/$ – see front matter ß 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.peptides.2008.10.022