Immunological characteristics of a C-terminal fragment of the Plasmodium falciparum blood-stage antigen Pf332

Abstract: Till date, there are no effective control strategies against the deadly disease of malaria, and millions of children across Africa, Oceania, Asia, and Latin America are at the mercy of this long term enemy of man every second that passes by. Other control measures combined with vaccination might help improve control strategy against malaria, but the development of vaccines face various challenges as well, due to the complexity of the parasites’ life cycle and other host factors. The asexual blood stage antigen Pf332 of Plasmodium falciparum, is expressed during the trophozoite stage, and transported from the parasitophorous membrane to the outer erythrocyte membrane during schizogony.Previous studies have suggested this antigen as a potential vaccine candidate, because Pf332-reactive human monoclonal antibody (mAb 33G2) inhibits parasite growth and cytoadherence in vitro. Elucidating and understanding the immunological capabilities of antigen Pf332, as a vaccine candidate was the aim of the studies presented in this thesis.In our first study we identified and characterized the immunogenicity of a non-repeat fragment of antigen Pf332, termed Pf332-C231, a 231 amino acids long fragment corresponding to 13 percent of the total protein. Various analyses carried out with this fragment reveal that recombinant C231 was immunogenic in rabbits. In addition, anti- C231 antibodies have in vitro inhibitory capabilities. In immunoflourescence and immunoblot assays, rabbit anti-C231 antibodies were able to recognize the native protein.In the other study, we examined the distribution of antibodies regarding recombinant C231 and crude P. falciparum extract in a malaria endemic area of Senegal. IgG antibody reactivity with crude P. falciparum antigen was detected in the sera of all the  donors while many of the children lacked or had low levels of such antibodies against C231. The distribution of the anti-C231 antibodies in the different IgG subclasses differed from that shown by crude P. falciparum antigen. The crude P. falciparum antigen gives a higher IgG3 response than IgG2 for all age-groups, while C231 gave similar levels of IgG2 and IgG3. Correlation studies showed that the levels of anti-C231antibodies were associated with protection from clinical malaria, but this only reached significance with IgE. These findings further emphasize the inclusion of antigen Pf332 as a subunit vaccine candidate against P. falciparum malaria.