Main B-cell epitopes of PvAMA-1 and PvMSP-9 are targeted by naturally acquired antibodies and epitope-specific memory cells in acute and convalescent phases of vivax malaria.

Although antibodies are considered critical for malaria protection, little is known about the mechanisms/factors that maintain humoral immunity, especially regarding the induction and maintenance of memory B cells over time. In Brazilian endemic areas, this is the first time that the profile of antibody responses and the occurrence of antigen-specific memory B cells (MBC) against P vivax were investigated during acute malaria and up to six months after parasite clearance. For this, we selected two peptides, PvAMA-1 and PvMSP-9 , which represent the apical membrane antigen-1 and merozoite surface protein-9 of P vivax, respectively. Both peptides were previously described as containing linear B-cell epitopes. Our findings were as follows: 1-both peptides were recognized by IgG antibodies at a high frequency (between 24% and 81%) in all study groups; 2-in the absence of infection, the IgG levels remained stable throughout 6 months of follow-up; and 3-PvAMA-1 and PvMSP-9 -specific MBCs were detected in all individual groups in the absence of reinfection throughout the follow-up period, suggesting long-lived MBC. However, no positive association was observed between malaria-specific antibody levels and frequency of MBCs over time. Taken together, these results suggest that peptides can be, in the future, an alternative strategy to polypeptidic vaccine formulation.