Infrared <i>IFP1</i>.<i>4</i> and <i>iRFP</i> genes are functionally expressed in <i>L</i>. <i>infantum</i> parasites.

<p>A) Growth rate of wild-type (WT; ▲) and stably-modified promastigotes IFP1.4+<i>L</i>.<i>infantum</i> (●) and iRFP+<i>L</i>.<i>infantum</i> (○). Parasites were counted using a Coulter counter. B) Correlation between fluorescence signal expressed as arbitrary units (AU) and the number of logarithmic IFP1.4+<i>L</i>. <i>infantum</i> (●) and iRFP+L. <i>infantum</i> (○) promastigotes in the presence of hygromycin B or after 6 months culture without drug IFP1.4+<i>L</i>. <i>infantum</i> (▲), iRFP+L. <i>infantum</i> (Δ). Two-fold serial dilutions were applied. C) Flow-cytometry analysis of intracellular amastigotes isolated from THP-1 <i>in vitro</i> infections with IFP1.4+<i>L</i>. <i>infantum</i> (red) and iRFP+<i>L</i>. <i>infantum</i> (green) strains. D) Mean fluorescence intensity emitted by lesion-derived amastigotes obtained from the engineered parasites. Experiments were carried out with 10⁷ parasites by triplicate and error bars represent standard deviations. Significance level *** p< 0,001; ** p<0.01; from two tails of Student <i>t</i>-test.