Persistence of Long-lived Memory B Cells specific to Duffy Binding Protein in individuals exposed to Plasmodium vivax.

The major challenge in designing a protective Duffy binding protein region II (DBPII)-based vaccine against blood-stage vivax malaria is the high number of polymorphisms in critical residues targeted by binding-inhibitory antibodies. Here, longevity of antibody and memory B cell response (MBCs) to DBL-TH variants, DBL-TH2, -TH4, -TH5, -TH6 and -TH9 were analyzed in P. vivax-exposed individuals living in a low malaria transmission area of southern Thailand. Antibody to DBL-TH variants were significantly detected during P. vivax infection and it was persisted for up to 9 months post-infection. However, DBL-TH-specific MBC responses were stably maintained longer than antibody response, at least 3 years post-infection in the absence of re-infection. Phenotyping of B cell subsets showed the expansion of activated and atypical MBCs during acute and recovery phase of infection. While the persistence of DBL-TH-specific MBCs was found in individuals who had activated and atypical MBC expansion, anti-DBL-TH antibody responses was rapidly declined in plasma. The data suggested that these two MBCs were triggered by P. vivax infection, its expansion and stability may have impact on antibody responses. Our results provided evidence for ability of DBPII variant antigens in induction of long-lasting MBCs among individuals who were living in low malaria endemicity.