Isolation and serological characterization of a Plasmodium vivax recombinant antigen.

A genomic library for Plasmodium vivax was constructed in lambda gt11 and immunologically screened with pooled serum samples from vivax patients. Six seroreactive clones were isolated, and one clone, denoted PV9, was studied further. This clone has an unusual base composition (65% G + C), does not share any homology with P. falciparum, and codes for an entirely new antigenic determinant. Antibodies (immunoglobulin G type) against the PV9-encoded polypeptide were produced in all vivax patients older than 15 years. This seroreactivity was lower among patients younger than 15 years (53%). The antigenic epitope(s) of the PV9-encoded polypeptide was recognized at a similar rate by serum samples from P. vivax patients who were living 350 to 973 km apart. Fifty percent of uninfected Indian adults were also seropositive, whereas all European and American (United States) sera tested were negative, suggesting that anti-PV9 antibodies persist after infection. The seroreactivity pattern of this antigen is similar to that of the immunity developed in malaria after repeated infections.