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Characterization of fine specificity of the immune response to a Plasmodium falciparum rhoptry neck protein, PfAARP

View Article: PubMed Central - PubMed

ABSTRACT

Background: Immunological characterization of potential blood-stage malaria antigens would be a valuable strategy in the development of an effective vaccine. Identifying B and CD4+ T cell epitopes will be important in understanding the nature of immune response. A previous study has shown that Plasmodium falciparum apical asparagine-rich protein (PfAARP) stimulates immune response and induces potent invasion-inhibitory antibodies. Antibodies to PfAARP provide synergistic effects in inhibition of parasite invasion when used in combination with antibodies to other antigens. In the present study, an attempt was made to identify B cell and CD4+ T cell epitopes of PfAARP.

Methods: Balb/c mice were immunized with recombinant PfAARP and both cellular and humoral responses were analysed at various time points. Computerized databases [immune epitope database (IEDB) and B cell epitope prediction (BCEPred)] were used to predict epitope sequences within PfAARP and predicted peptides were synthesized. In addition, nine 18 amino acid, long-overlapping peptides spanning the entire length of PfAARP were synthesized. Using these peptides, B cell and CD4+ T cell responses in PfAARP immunized mice were measured by ELISA and ELISPOT assays.

Results: Here, it is demonstrated that immunization of mice with PfAARP induced long-lasting, high-titre antibodies (4 months post immunization). Also, the recombinant protein was effective in inducing a pronounced Th1 type of immune response quantified by IFN-γ ELISA and ELISPOT. It was found that the predicted peptides did not represent the immunogenic regions of PfAARP. However, of the nine overlapping peptides, three peptides (peptides 3, 5 and 7) were strongly recognized by PfAARP-immunized sera and represented B cell epitopes. Also, peptide 3 elicited IFN- γ response, suggesting it to be a T-cell epitope.

Conclusions: Induction of long-lasting humoral and cellular response on PfAARP immunization in mice underscores its possible use as a blood-stage malaria vaccine candidate. Mapping of immunogenic regions may help in designing fusion chimera containing immunologically relevant regions of other vaccine target antigens and/or for multi-component vaccine candidates.

No MeSH data available.


Epitope prediction and peptide synthesis. a B and T cell epitopes were predicted by IEDB and BCEPred. b Selected peptides were synthesized using Fmoc methodology and their purity was determined by RP-HPLC
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Fig4: Epitope prediction and peptide synthesis. a B and T cell epitopes were predicted by IEDB and BCEPred. b Selected peptides were synthesized using Fmoc methodology and their purity was determined by RP-HPLC

Mentions: Since a robust humoral and cellular immune response is generated in mice immunized with PfAARP, it was next attempted to determine linear minimal immunogenic regions of the protein. Two B cell epitopes (10–15 residues) were predicted by BCEPred and one epitope (16 residues) by IEBD (Fig. 4a). Also, ten helper T cell epitopes (15 residues) were predicted by IEDB-recommended prediction method and four helper T cell epitopes by SMM-align method to the three alleles of H-2I MHC locus of mice (Fig. 4a). Peptides predicted as B and T cell epitopes mainly overlapped in two fragments of PfAARP, of which one was localized in the centre and other in C-terminus of the protein. Therefore, two peptides corresponding to residue 32–47 and 92–107 were synthesized (Peptide A and B) by standard solid phase methods [23]. Peptide purity was analysed by RP-HPLC and was shown to be >90 % (Fig. 4b).Fig. 4


Characterization of fine specificity of the immune response to a Plasmodium falciparum rhoptry neck protein, PfAARP
Epitope prediction and peptide synthesis. a B and T cell epitopes were predicted by IEDB and BCEPred. b Selected peptides were synthesized using Fmoc methodology and their purity was determined by RP-HPLC
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5015194&req=5

Fig4: Epitope prediction and peptide synthesis. a B and T cell epitopes were predicted by IEDB and BCEPred. b Selected peptides were synthesized using Fmoc methodology and their purity was determined by RP-HPLC
Mentions: Since a robust humoral and cellular immune response is generated in mice immunized with PfAARP, it was next attempted to determine linear minimal immunogenic regions of the protein. Two B cell epitopes (10–15 residues) were predicted by BCEPred and one epitope (16 residues) by IEBD (Fig. 4a). Also, ten helper T cell epitopes (15 residues) were predicted by IEDB-recommended prediction method and four helper T cell epitopes by SMM-align method to the three alleles of H-2I MHC locus of mice (Fig. 4a). Peptides predicted as B and T cell epitopes mainly overlapped in two fragments of PfAARP, of which one was localized in the centre and other in C-terminus of the protein. Therefore, two peptides corresponding to residue 32–47 and 92–107 were synthesized (Peptide A and B) by standard solid phase methods [23]. Peptide purity was analysed by RP-HPLC and was shown to be >90 % (Fig. 4b).Fig. 4

View Article: PubMed Central - PubMed

ABSTRACT

Background: Immunological characterization of potential blood-stage malaria antigens would be a valuable strategy in the development of an effective vaccine. Identifying B and CD4+ T cell epitopes will be important in understanding the nature of immune response. A previous study has shown that Plasmodium falciparum apical asparagine-rich protein (PfAARP) stimulates immune response and induces potent invasion-inhibitory antibodies. Antibodies to PfAARP provide synergistic effects in inhibition of parasite invasion when used in combination with antibodies to other antigens. In the present study, an attempt was made to identify B cell and CD4+ T cell epitopes of PfAARP.

Methods: Balb/c mice were immunized with recombinant PfAARP and both cellular and humoral responses were analysed at various time points. Computerized databases [immune epitope database (IEDB) and B cell epitope prediction (BCEPred)] were used to predict epitope sequences within PfAARP and predicted peptides were synthesized. In addition, nine 18 amino acid, long-overlapping peptides spanning the entire length of PfAARP were synthesized. Using these peptides, B cell and CD4+ T cell responses in PfAARP immunized mice were measured by ELISA and ELISPOT assays.

Results: Here, it is demonstrated that immunization of mice with PfAARP induced long-lasting, high-titre antibodies (4 months post immunization). Also, the recombinant protein was effective in inducing a pronounced Th1 type of immune response quantified by IFN-γ ELISA and ELISPOT. It was found that the predicted peptides did not represent the immunogenic regions of PfAARP. However, of the nine overlapping peptides, three peptides (peptides 3, 5 and 7) were strongly recognized by PfAARP-immunized sera and represented B cell epitopes. Also, peptide 3 elicited IFN- γ response, suggesting it to be a T-cell epitope.

Conclusions: Induction of long-lasting humoral and cellular response on PfAARP immunization in mice underscores its possible use as a blood-stage malaria vaccine candidate. Mapping of immunogenic regions may help in designing fusion chimera containing immunologically relevant regions of other vaccine target antigens and/or for multi-component vaccine candidates.

No MeSH data available.