IgG antibody profile to c-terminal region of Plasmodium vivax merozoite surface protein-1 in Thai individuals exposed to malaria.

Naturally acquired immune response to C-terminal region of Plasmodium vivax merozoite surface protein1 (PvMSP1) in 200 individuals with recent clinical episodes of malaria from malaria endemic areas along Thai-Myanmar border in the west and Thai-Cambodia border in the east of Thailand was evaluated by enzyme-linked immunosorbent assay (ELISA). The anti-PvMSP1-IgG antibody was observed in 110 individuals (55%). Among IgG responders, IgG1 coexpressed with IgG3 were the predominant subclasses. The levels of anti-PvMSP1 total IgG, IgG1 and IgG3 antibody response seem to be increased with age although no detectable significant correlation was found (r = 0.004, p = 0.484 for total IgG; r = 0.035, p = 0.386 for IgG1; r = -0.600, p = 0.142 for IgG2; r = 0.077, p = 0.227 for IgG3; r = 0.664, p = 0.051 for IgG4). However, the mean level of specific total IgG was highest in the age group of >40 years. These levels of either specific total IgG or each IgG isotype did not vary among individuals with different malaria episodes. A higher level of specific total IgG, IgG1 and IgG3 antibody response related with the lower of parasitemia density was observed although no significant correlation was found. Our data indicate that individuals exposed to vivax malaria in Thailand developed antibodies to the potential candidate vaccine antigen, PvMSP1 (C-terminal).