p_BoF,il.FS_OF tcq AND tGM ANTTBODIES TO PV66/AMA-1 lN INDIVIDUAIS NATURATLY TNFECTED WITH PLASMODIUM VIVAX FROM SRI LANKA

Abstract

An understanding of the natural immune response to vaccine candidates is important in vaccine development. Recombinant protein, PV66/AMA-1, representing native Apical Membrane Antigen-'l of Plasmodium vivax, was used in an antibody sandwich ELISA to assess the lgC14 and lgM isotype responses of acute P. vivax malaria patients from two malaria endemic areas of the iiland, Anuradhapura (n:40) and Kataragama (n:46), and from a non-endemic area Colombo (n.t47). A significantly (PcO.OS) highei magnitude and prevalence of the lgM response was observed in non-endemic individuals ihan in residents from both endemic areas' The prevalence and magnitude of cytophilic lgCl and lgG3 antibodies to PV66/AMA-1 in endemic residents were significantly higher (P<0.05) than the corresponding non-cytophilic lgC2 and lgC4 isotypes. Aithough the reiponding proportions of lgCl and lgG3 within each test area were not significantly different (P>0.05), most individuals showed a bias towards the lgCl response in magnitude compared to their lgC3 response. ln the endemic areas, prevalence of lgM markedly diminished with increasing exposure and was minimal in those with more than five past infections. ln parallel, their prevalerrce of lgCl and lgC3 antibodies increased after experiencing the first malaria infection. This isotype switch was not evident in the non-endemic individuals. Thus, under unstable malaria conditions prevalent in the endemic areas of the island, it is apparent that with increasing exposure to malaria, the bias of the anti-PV66/AMA-1 antibody response was tglvards the functionally important cytophilic lgCl isotyp