Identification of B cell protective antigens/epitopes against asexual and sexual blood forms of Plasmodium parasites through monoclonal antibodies
The main aim of the present proposal is to identify novel protective Plasmodium antigens from asexual and sexual blood forms using monoclonal antibodies (mAbs). Those mAbs will be cloned from single plasma cells of P. berghei-immune mice treated with pirimethamine or mice immunized with gamete protein extract. This is an unprecedented approach in the identification of novel antigens/epitopes for the asexual and sexual blood phases of malaria. Blood or spleen single IgG-secreting cells will be isolated for Ig V(D)J cloning and mAb production. After verifying mAb specificity and functionality, targeted antigens will be solved by mass spectrometry. Once identified a novel antigen, its ortholog gene will be assayed regarding parasitic fitness and ability to elicit protection as vaccine candidate against parasites that cause malaria in humans.
As more parasite exposures occur in endemic areas, higher are the malarial-specific antibody titers which may attenuate disease symptoms but do not inhibit transmission to mosquitoes. Numerous parasite protein variants are expressed upon Plasmodium infection stimulating the polyclonal activation of B cells. Nonetheless, this event seems to induce B cell exhaustion. Associated with this reduction of B cell functionality, alterations have been observed in the profile of cytokine expression, such as type I IFN, and frequency of B cell populations. Among the major B cell subsets affected by cellular exhaustion are memory, germinal centre and antibody-secreting cells, culminating with diminished antibody titers previously generated. On the other hand, serum samples of chronically malaria-exposed adults have the ability to protect children from developing severe disease. Antigens from extracellular merozoites, infected erythrocytes and gametocytes are the main targets of this protective humoral response. Some P. falciparum and P. vivax antigens have been identified as targets for this response in the last decades. But none of them showed great protective capacity in clinical trials yet. Low immunogenicity, difficulty in generating proteins with tertiary conformation, required for humoral responses to structural epitopes, and lack of protective correlates have been associated with that reduced efficacy in the target screening.