| Malaria is a protozoal disease that is widely spread throughout the world and seriously endangers human health.Historic progress in malaria prevention and control has been obtained in the past 20 years,but malaria remains a major public health problem.Recently,the increasing resistance of Anopheles mosquitoes to insecticides and the wide spread of artemisinin-resistant strains made the need for development of a potent malaria vaccine more urgent.However,most of the existing malaria vaccine candidate antigens are highly immunogenic proteins discovered by serological screening,and malaria vaccines based on these antigens have poor clinical protective effects.The development of a powerful malaria vaccine requires further research on the immunogenicity of the malaria antigens and the discovery of newly vaccine candidate antigens.Invasion of erythrocytes by Plasmodium falciparum is an essential step for its successful proliferation and transmission.merozoite antigens presented on the surface establish the contact between parasite and erythrocytes and are direct targets of naturally acquired humoural immunity.Therefore,the key proteins of merozoite invasion is potential targets for malaria vaccine development.We conducted a large-scale linear epitope mapping using overlapped peptide microarrays to study the B-cell linear epitopes of the key invasion-related merozoite proteins.Epitopes containing repetitive sequences and glutamate-rich motifs were found highly antigenic and tended to be decoy epitopes that drive the host humoral immunity away from the functional domains.The results indicated highly antigenic parasite proteins derived from serological screening may not be appropriate targets for malaria vaccines.In this study,we firstly carried out invasion inhibition assay to confirm the above findings.20 peptides from 14 merozoite proteins that contain highly antigenic epitopes were selected as immunogens for generation of specific antibodies.Most of these antibodies showed no inhibitory effect on parasite invasion,while antibodies specific to the peptides from the red blood cell-binding sites of MESA,an essential invasion protein,showed invasion-inhibitory effect.The results confirmed that the humoural immunity induced by highly antigenic epitopes of Plasmodium may not generate successful protection,and antibodies against functional sites of parasite proteins with low antigenicity may be more superior to be cantidate for malaria vaccine.In order to discover novel malaria vaccine candidates,the expression pattern of the total genes of Plasmodium falciparum 3D7 strain was screened.Our team has obtained the accurate transcriptome of the total 5034 genes from the 14 chromosomes of PF3D7.In this study,we further analyzed the genes,derived from choromosome 14,that highly expressed in merozoites,compared to schizonts and trophozoite.A large group of genes with unkown function were found to have abundant expression specifically in merozoite.Among these genes,64 were unknown.Totally 13 recombinant proteins coding by these genes were successfully generated and the relevant specific polyclonal antibodies were prepared.The expression pattern of these novel merozoite proteins and their functions were studied.Most of the proteins were found to express on the surface of merozoite.Monoclonal antibodies against these proteins can effectively interfere the invasion of parasite.This study revealed the role of malaria high-antigenic epitopes in the immune escape of Plasmodium falciparum.It was proposed that the discovery of candidate antigens for malaria vaccine should not only base on the immunogenicity,but should focus on the function.Three novel merozoite proteins were discovered to play important roles during the invasion of erythrocytes.These findings provide valuable targets and theoretical basis for the establishment of novel malaria vaccines. |
