FIG 4.

PfClag9 elicits protective immunity in P. berghei. (A) Naturally acquired humoral IgG immune responses to proteins of PfClag9 fragments. Human IgG antibodies against different fragments of PfClag9 were detected by ELISA in sera from naturally infected patients from Liberia and India. Sera from Denmark were used as negative controls. The positivity thresholds represented by dotted lines were determined from the mean reactivities (+2 standard deviations) of 28 serum samples from nonimmune Danish volunteers. (B) PfClag9d-immunized mice showed delayed death upon P. berghei challenge. Four mice were immunized with PfClag9d and challenged with 1 × 10⁴ P. berghei (ANKA)-infected RBCs administered intraperitoneally. Four mice immunized with PBS with Freund’s adjuvant served as controls. (i) Kaplan-Meier curve of the overall survival of mice in each group. (ii) Parasitemia levels on different days after P. berghei challenge, in control and PfClag9d-immunized mice. The t test was performed on the parasitemia levels, and the P value was calculated to be 0.00075. (C) Model of the PfRhopH-Clag9 complex, based on protein-protein interactions and protein-erythrocyte interactions.