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20 Banyal and Elangbamparasite in the human host other than the sporozoitemaking it a visible target for antibodies. Antibodiestargeting Mz proteins, mainly its surface proteins,interfere in the invasion process through agglutinationfollowed by phagocytosis or blocking of Mzerythrocyteinteraction. Several Mz surface proteinshave been identified and some are targets for leadingmalaria candidate vaccines.Mz surface proteins (MSP): MSP-1 is the mostabundant protein on the surface of Mzs (Polley et al.,2003). It is a 190230 kDa protein on the surface of Mzthat is processed into smaller fragments at the time ofinvasion of erythrocytes and exists as a non-covalentlylinked complex of four fragments (83, 28, 34 and 42kDa). The C-terminal 42 kDa fragment (MSP-142)undergoes further processing to form MSP-1 33, whichis shed, and MSP-1 19, which remains on the Mz surfaceand is taken into the newly invaded erythrocytes.Monoclonal antibodies to MSP-1 19 inhibit Mzinvasion in vitro, and sera from P. falciparum immuneMSP-2 is encoded by a single gene and is a 4552 kDaintegral membrane glycoprotein anchored on thesurface of Mz by a glycosylphosphatidyl inositol(GPI) moeity (Weisman et al., 2001) and a target ofhost protective immune responses as monoclonalantibodies specific to MSP-2 have inhibited parasitesgrowth in vitro. Mice immunized with conservedregions of P. falciparum MSP-2 have been protectedagainst challenge with P. chabaudi. Antibodies toMSP-2, mainly IgG 3, have been detected in sera ofpeople living in endemic areas. Human trials of multisubunit vaccines containing MSP-2 have beenundertaken both in non-exposed and malaria-exposedindividuals (Genton et al., 2000).MSP-3 is a secreted polymorphic antigen associatedwith erythrocytic schizonts and Mzs. P. falciparumMSP-3 has been shown to range from 40-76 kDadepending on the isolate and has been implicated ininduction of ADCI (Audran et al., 2005; Druilhe et al.,2005). P. vivax MSP-3 is associated with but notadult humans and P. chabaudi immune mice revealed aanchored in the Mz membrane and is structurallymajor role for MSP-1 specific antibodies inrelated to P. falciparum MSP-3 and 140 kDa MSP of P.19knowlesi (Galinski et al., 1999).mediating the invasion-inhibition (O'Donnell et al.,2001). The 19 kDa fragment is reported to be highly P. falciparum MSP-4 is a 40 kDa protein containing aconserved in P. falciparum and contains a series of single epidermal growth factor (EGF)-like domain atcysteine residues that are conserved among species ofplasmodia infecting humans, primates and rodents(Daly et al., 1992).Different effector mechanisms of antibodies againstMSP-1 are being suggested which primarily involveinhibition of erythrocyte invasion by Mzs (Tolle et al.,1993; Locher et al., 1996; O'Donnell et al., 2001;Vukovic et al., 2003), blocking the processing oflarger mature MSP-1 protein on the Mz surface(Blackman et al., 1994) and through macrophage Fcreceptors to induce ADCC (Bouharoun-Tayoun et al.,1995; Ravetch and Clynes, 1998). MSP-119-specificimmunoglobulin IgG 3 monoclonal antibody canpassively transfer protection to mice deficient in Fc-ãRI receptors whose macrophages cannot bind IgG 3(Vukovic et al., 2000). Studies in P. yoelii model byWipasa et al. (2002) show that antibodies specific toMSP-1 19 alone can induce protective immunity and Proteolytic processing of MSP-1 precursor producesthat effector T-cells specific to MSP-1 19 play no role in two components p 36 (MSP-636) and p 22 (MSP-722)immunity. However, such antibodies must be which are associated with the shed MSP-1 complex.the C-terminus that is synthesized at the late ring stageand transported to the parasite surface, anchored to theMz membrane by a GPI moiety. Studies analyzed aregion of chromosome 2 in P. falciparum andidentified 3 clustered genes that encode GPI-anchoredMz surface proteins in tandem MSP-2, MSP-5 andMSP-4 and MSP-5 encoding a 40 kDa protein locatedon the Mz surface (Marshall et al., 1998). Ahomologue of P. falciparum MSP-4 and MSP-5 in P.chabaudi designated Pc MSP 4/5 encoding a protein ofapparently 36 kDa contains a single EGF-like domainnear the C-terminus. Murine homologue of MSP-4induces protective immunity in mice against lethalchallenge with P. yoelii. Anti-MSP-4 antibodies arehighly prevalent and present at high level inindividuals in malaria endemic area and are mainlyIgG 1 and IgG 3.produced during challenge. Specific cellular immune The 36 kDa protein is derived from a larger precursorresponses induced by MSP-1 can be protective against MSP-6 and so designated as MPS-6 36. Antibodiesexoerythrocytic forms of P. yoelii (Kawabata et al., against recombinant protein containing the C-terminal2002). of MSP-6 36 bound to parasite surface or theparasitophorous vacuole within schizonts (Trucco et