The development of modular constructs that include antigenic regions targeted by protective immune responses is an attractive approach for
subunit vaccine development. However, a main concern of using these
vaccine platforms is how to preserve the antigenic identity of conformational
B cell epitopes. In the present study we evaluated naturally acquired antibody responses to a chimeric
protein engineered to contain a previously defined
immunodominant domain of the Plasmodium vivax reticulocyte binding protein-1 located between
amino acid positions K435-I777. The construct also includes three regions of the cognate
protein (F571-D587, I1745-S1786 and L2235-E2263) predicted to contain MHC class II promiscuous
T cell epitopes. Plasma samples from 253 naturally exposed individuals were tested against this chimeric
protein named PvRMC-RBP1 and a control
protein that includes the native sequence PvRBP123-751 in comparative experiments to study the frequency of total
IgG and
IgG subclass reactivity.
HLA-DRB1 and
HLA-DQB1 allelic groups were typed by PCR-SSO to evaluate the association between major HLA class II alleles and antibody responses. We found
IgG antibodies that recognized the chimeric PvRMC-RBP1 and the PvRBP123-751 in 47.1% and 60% of the studied population, respectively. Moreover, the reactivity index against both
proteins were comparable and associated with time of exposure (p<0.0001) and number of previous
malaria episodes (p<0.005).
IgG subclass profile showed a predominance of cytophilic
IgG1 over other subclasses against both
proteins tested. Collectively these studies suggest that the chimeric PvRMC-RBP1
protein retained
antigenic determinants in the PvRBP1435-777 native sequence. Although 52.9% of the population did not present detectable titers of
antibodies to PvRMC-RBP1, genetic restriction to this chimeric
protein does not seem to occur, since no association was observed between the
HLA-DRB1* or
HLA-DQB1* alleles and the antibody responses. This experimental evidence strongly suggests that the identity of the conformational
B cell epitopes is preserved in the chimeric
protein.