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
