L. major tor3− mutant has highly attenuated virulence during the amastigote stage. (A) Increase in footpad thickness after inoculation of 105 purified PNA− metacyclics into Balb/C mice; WT (■), WT/+TOR3 (◆), two clonal lines of tor3− (□, △) and tor3−/+TOR3 (○,●). SEs are shown (n = 4). (B) Parasitemia was measured by limiting dilution assay at day 21 postinfection in an experiment similar to that shown in (A), except that the inoculums was 106 stationary phase cells/foot. SEs are shown (n = 4). (C) Macrophage infections. WT (■), WT/+TOR3 (◆), tor3− (△) and tor3−/+TOR3 (○). Three independent experiments were performed, with triplicate samples within each; data show results of one representative experiment. Bars indicate SEs for triplicate wells.