FIG. 1.

Inhibition of DBPII binding to Duffy-positive erythrocytes by human sera from Papua New Guinea. Individual sera were tested at a dilution of 1:10 for inhibition of binding in an in vitro assay (COS7 cell assay). Sera were classified based on their responses to recombinant DBP as determined by ELISA, as follows: high responders (black bars), low responders (dark gray bars), and nonresponders (light gray bars). Sera showed marked differences in inhibitory efficacy, and the differences in inhibition did not correlate with antibody titers. Binding inhibitory effects were classified as follows: major effect, ≥80% inhibition; moderate effect, 40 to 80% inhibition; and minor or no effect, 0 to 40% inhibition. The sample numbers used are not the same as those in Table 1.