Naturally acquired humoral and cellular immune responses to Plasmodium vivax merozoite surface protein 9 in Northwestern Amazon individuals

Abstract

Antibody and T-cell reactivities to Plasmodium vivax merozoite surface protein 9 (PvMSP9) were evaluated in a cross-sectional study of individuals naturally exposed to malaria infections living in Ribeirinha, a native riverine community and in Colina, a transmigrant community, Rondonia, Brazil. The antibody responses to PvMSP9-RIRIIand PvMSP9-Nt domains in Ribeirinha were higher compared with Colina and correlated with age and time of malaria exposure. IgG2 was most prevalent for PvMSP9-RII in both communities, and IgG1 was the predominant isotype for PvMSP9-Nt and PvMSP9-RIRII in Ribeirinha. IFN-gamma and IL-4 predominated in Ribeirinha, while IFN-gamma predominated in Colina. Variation in exposure to P. vivax likely accounts for the differences observed in cytokine and antibody levels between the two populations studied.

Figure 1

Schematic representation of PvMSP9, the constructs of recombinant proteins used for serological analysis (continuous lines) and the synthetic peptides used for cellular analysis (discontinuous lines).

Figure 2

Antibody responses to the recombinant proteins PvMSP9-RIRII, PVMSP9-RII and PvMSP9-Nt in malaria exposed individuals from Colina (CO) and Ribeirinha (RI). (a) Frequency of IgG positive individuals to the recombinant proteins. (*) indicate that the difference was significant (p<0.0001) for a comparison between the frequency of responders from Colina with Ribeirinha by χ² test; (b) IgG antibodies measured as mean reactivity indexes in responders (mean ± 95% confidence interval). (+) indicate that the difference was significant (p<0.05) for a comparison between the mean RI values responders from Colina with Ribeirinha by Student’s t test; (c) Frequency of IgG subclass distribution in IgG positive individuals. (#) indicates that the difference was significant (p<0.01) for a comparison between a particular IgG subclass over the others IgG subclasses for the same recombinant protein.

Figure 3

Spearman’s rank correlation between time of residence in malaria endemic area and the IgG reactivity index against PvMSP9-RIRII and PvMSP9-RII in Colina (a and c) and Ribeirinha (b and d) population.

Figure 4

Elispot IFN-γ and IL-4 responses to PvMSP9 synthetic peptides (pE, pH, pJ, pK and pL) in individuals naturally exposed to malaria infection from Colina and Ribeirinha. Frequency of IFN-γ and IL-4 responders for each peptide in individuals from Colina (a) and Ribeirinha (b). (*) Indicates that the difference was significant (p<0,01) for a comparison between the frequency of IFN-γ responders with IL-4 responders for each peptide calculated by χ² test.