Addition of DHF or THF to the culture medium increases the proliferation of P. falciparum, but does not alter the sensitivity to ketotifen. A) Growth of wild-type and ΔPfgABCG2-hDHFR (i) P. falciparum parasites over 72 h, measured in the presence of increasing concentrations of DHF or THF and in the absence of ketotifen. Mean and standard deviation (SD) values of biological triplicates are shown. ***, p < 0.001; **, p < 0.01; ns, not significant (Student's unpaired t-test). B) Proliferation of asexual blood-stage parasites measured over 72 h in the presence of a range of ketotifen concentrations, and in the presence or absence of 50 nM DHF or THF. “ΔPfgABCG2″ refers to ΔPfgABCG2-hDHFR (i) parasites. Mean and standard deviation (SD) values of biological triplicates are shown.