Clinical and epidemiological studies on a 47kD Plasmodium falciparum antigen.

Abstract

Sera were taken at random intervals from a Japanese patient during the acute to convalescent phases of falciparum malaria. Western blotting study revealed that the 47kD antigenic polypeptide of the parasite was strongly presented by the sera taken during the acute phase of the infection, while the 47kD band became faint as the phase progressed, and serum taken 2 months after the onset of the disease was only weakly reactive to the molecule. During the observation period, the indirect fluorescent antibody titer invariably persisted at 1 : 256. The reactivity of the serum samples taken at hypo, meso and hyperendemic localities in Sudan was tested by the same method. Regardless of the endemic backgrounds, sera from examinees with currently existing parasitemia or high antibody titers measured by an avidin biotin peroxidase complex enzyme-linked immunosorbent assay (ABC-ELISA), reacted to the 47kD antigenic polypeptide, whereas low-titered sera did not present the 47kD band. Some high-titered sera from the meso or hyperendemic locality showed no reactivity to the 47kD antigen. It was presumed that the high antibody titer of this group was a reflection of accumulated past malaria infections but not of currently active malaria or recent past infection. The 47kD molecule is a useful parasite antigenic polypeptide in terms of defining present and/or recent past infection in the serological survey of malaria.