TABLE 3.

Susceptibility to antimony in intracellular amastigotes of L. major lines^a

Metal	Mean EC50 (μM) ± SD (RI)b
	pUCNEO	LABCG2	LABCG2rev 90D
SbIII	6.16 ± 0.07	21.30 ± 0.81 (3.4)*	5.90 ± 0.11 (0.9)
SbV	76.14 ± 2.88	>200 (>2.6)*	87.73 ± 9.71 (1.1)

^aMacrophage-differentiated THP-1 cells infected with L. major lines using a macrophage/parasite ratio of 1:10 were incubated for 3 days in the presence of Sb^III or for 5 days in the presence of Sb^V at different concentrations, as described in Materials and Methods. Antimony susceptibility was determined from the percentage of infected cells and the number of intracellular amastigotes per cell in antimony-treated cultures versus nontreated cultures. Infection was determined by DAPI staining of 300 macrophages/well.

^bResistance indexes (RI) were calculated by dividing the EC₅₀ for the Leishmania line overexpressing LABCG2 and LABCG2rev 90D by that for the Leishmania control line (pUCNEO). Data are the means ± standard deviations of results from two independent experiments. Significant differences were determined by using the Student t test (*, P < 0.01).