Studies on Plasmodium falciparum asexual blood stage antigens: RAP-2/RSP-2 and Pf332 in focus

All previously published papers were reproduced with permission from the publishers. SUMMARY Malaria remains a challenging health problem in malaria endemic regions. The life cycle of the malaria parasite is very complex and provides a number of potential targets for vaccination. Several antigens have been studied and characterised in this context. Existing data suggest that antibodies are instrumental in the control of infection, but could also be responsible for pathogenesis. The mechanisms by which the antibodies mediate their effects are known to differ, largely depending on the target antigen. In this thesis, data on two plasmodial asexual blood stage antigens (RAP-2/RSP-2 and Pf332-C231) are presented and their putative roles in disease manifestation and/or control. Infection with malaria invariably leads to anaemia, involving the destruction of both normal and infected erythrocytes by various mechanisms. The groups most at risk of developing malarial anaemia include children below the age of five years and pregnant women. A partial aim of the work presented herein was to investigate the mechanisms responsible for the destruction of erythroid cells during anaemia, and more specifically to define the role of the rhoptry associated protein (RAP/RSP)-2 and other members of the low molecular weight rhoptry associated protein (RAP) complex, RAP-1 and-3 in processes resulting in anaemia. Antibodies to the RAP complex were shown to have the potential to mediate the destruction of RAP-2/RSP-2-tagged erythroid cells by phagocytosis or by complement activation and lysis. In addition, antibodies to RAP-1 and RAP-2/RSP-2 could induce the apoptotic death of RAP-2/RSP-2-tagged erythroblasts. The frequency and functionality of naturally occurring RAP-2/RSP-2 antibodies in the sera of anaemic and non-anaemic Cameroonian children were also investigated. All sera tested contained RAP-2/RSP-2 reactive antibodies by both immunofluorescence and flow cytometry. The anaemic group of children had significantly higher levels of antibodies of the IgG isotype than the non-anaemic individuals, while the levels of IgM were similar in both groups. With respect to IgG subclasses, low levels of IgG-1 and-3 antibodies were detected. Higher levels of IgG3 were seen in the non-anaemic individuals as compared to anaemic subjects. With regard to antibody functionality, the non-anaemic individuals recognised a greater proportion of RAP-2/RSP-2-tagged erythrocytes and activated complement to a greater extent than the anaemic individuals. These data suggest a role for RAP antibodies in both pathogenesis and protection during malaria. Earlier studies observed that humans continuously exposed to malaria, recognised Pf332 extensively. Further studies revealed that Pf332 antibodies …