Figure 2.
Virulent Type I strains of T. gondii resist macrophages-mediated parasite elimination. (A) Comparison of infection rate (left panel) and number of parasites per vacuole (right panel) between PTG (Type II) and RH (Type I) at 0h, 13h and 26h following a 15-minute pulse infection. The graphs are from one of three representative experiments and error bars correspond to standard error for three mice. (B) Comparison of infection rate between Type I strains RH and GT-1, Type II strains PTG and PE and Type III strains CTG and VEG at 1h and 26h following pulse infection. Data are representive of three independent experiments. (C) Ultrastructural microscopic analysis of PTG (left panel) and RH (right panel) at 1h and 4h post invasion in CPS-primed wildtype macrophages. About 40 parasite profiles per time point were classified as either residing in an intact PVM or in disrupted vacuoles or with the parasite membrane itself being disrupted. Nearly all RH vacuoles remained intact 4h post infection (right panel). (D) The integrity of the vacuoles formed by avirulent GFP-PTG (left panel) and virulent GFP-RH (middle panel) parasites was monitored using anti-GRA-7 (Alexa Fluor 568, shown in red) staining 1h post infection of CPS-primed macrophages. In the right-hand panel, over 100 vacuoles were counted per time point and data is representative of two independent experiments. (E) Primed peritoneal macrophages were infected with DsRed-RH first for 15 min, washed and then infected with GFP-PTG 30min later. One hr post-PTG infection cells were stained with anti-GRA-7 antibodies (Alexa Fluor 647, shown in magenta). The left most picture shows a macrophage containing a single intact GRA7+ RH vacuole (yellow arrow) and two disrupted GRA-7-negative GFP-PTG vacuoles (white arrows). The kinetics of vacuolar disruption of GFP-PTG (middle panel) and DsRed-RH (right panel) in singly and dually infected cells is shown. The percentage of GRA-7+ vacuoles in a total of 100 vacuoles per time point was scored at 1 and 6 hr post infection in either RH or PTG singly infected macrophages or in RH and PTG dually infected macrophages.