Figure 3.

Jasplakinolide reversibly blocks tachyzoite entry into host cells. Tachyzoites were treated with 1 μM jasplakinolide for 10 min (37°C) before being added to human foreskin fibroblasts and allowed 30 min to invade still in the presence of drug. Control cultures had an equivalent amount of DMSO added. All extracellular parasites (both free and those attached to the host-cell surface) were removed by washing the monolayers several times with clean medium, and the cultures were incubated for ≈6 h (A and B) or 24 h (C) at 37°C before parasite numbers were counted. Jasplakinolide caused significant inhibition of parasite entry, as determined by both the percentage of infected host cells (A) and the numbers of parasites per host cell (B). Note in A, ∗∗, percentage of infected host cells significantly different from controls, P > 0.001. (C) When jasplakinolide and all free unattached parasites were removed from the cultures, those parasites bound to the host cells were able to invade and replicate in the host cells in an identical manner to untreated control cultures. Counts of the numbers of parasites per vacuole after 24 h. In all cases, the results represent the means ± SD from three replicate experiments.