The ring-infected erythrocyte surface antigen (RESA) polypeptide of Plasmodium falciparum contains two separate blocks of tandem repeats encoding antigenic epitopes that are naturally immunogenic in man.

We showed previously that the ring-infected erythrocyte surface antigen (RESA) of Plasmodium falciparum contains a repetitive amino acid sequence. We have investigated here the sequence and antigenic relationships between RESA from FC27, a Papua New Guinea isolate, and from NF7, a Ghanaian isolate. The complete nucleotide sequences of eight different cDNA clones demonstrate that RESA from the two strains are closely homologous over the region that can be compared. A series of related eight, four and three amino acid repeats is located at the 3' end, forming the C terminus of RESA in FC27. RESA contains a second block of repeats based on an 11 amino acid sequence and separated from the 3' block by 381 amino acids in NF7. Antibodies from Papua New Guineans react with RESA from the African isolate, and vice-versa. Antigenic determinants that are naturally immunogenic in man are present in the 5' repeats of RESA, as well as in the 3' repeats, and antibodies that cross-react with both blocks of repeats were detected by reacting affinity-purified human antibodies with cloned subfragments of the cDNA clones, expressed in Escherichia coli.