FIG. 2.

Long-term changes in levels of plasma antibodies recognizing PfEMP1-like molecules on the surface of intact RBC infected with late developmental stages of P. falciparum as detected by flow cytometry. The reactivity of plasma from three individuals selected for low (E2, left column), medium (2P4, center column), and high (2N3, right column) antibody levels with four parasite isolates collected in 1994 (S9457, top row), 1995 (Z453, second row; Z455, third row), and 1996 (Y372, bottom row) are shown. The x axis shows the date. The y axis shows the anti-PfEMP1-like antibody reactivity (mean flow cytometer channel number). The negative cutoff (mean + 2 standard deviations for five plasma samples from unexposed individuals) is shown as a dotted horizontal line. The level of anti-PfEMP1-like antibodies in a pool of hyperimmune plasma (positive control) is shown as a dashed horizontal line. Solid vertical lines indicate clinical episodes of malaria.