FIG. 4.

Spatial and temporal distribution of luciferase activity in mice infected with a lethal parasite inoculum. (A) Monitoring of F-Luc and R-Luc activities during the early phase of T. gondii infection. Mice (CD1) were infected using 10⁶ H3F33 tachyzoites and analyzed by BLI for four consecutive days after administration of substrates selective for bradyzoite (d-luciferin, upper row) and tachyzoite (coelenterazine, lower row) transcribed luciferase genes. The scale of the signal intensity (color bar) for F-Luc was set at between 5,000 and 30,000 photons/s/cm²/sr, whereas that for R-Luc was set at between 10,000 and 50,000 photons/s/cm²/sr. The experiment shown was conducted in triplicates. Uninfected animals were included to quantify the photon emission background (first mouse from the left in each panel). (B) Animals infected i.p. with 10⁶ H3F33 tachyzoites were analyzed daily for photon emission to monitor bradyzoite formation. The panels show dorsal and ventral BLI analysis of a representative mouse. In this mouse the number of brain cysts determined microscopically after death at day 16 postinfection was about 21,500. The scale of the signal intensity (color bar) is included. (C) Time course of F-Luc photon emission activity from individual mice infected with 10⁶ H3F33 tachyzoites (color coded M1 to M4). Photon emission counts (p/s) were collected daily over a period of 40 days from an area of the head (region of interest) encompassing the brain (inset). As a control, photon emission values were collected from the same region of interest of uninfected mice (unM).