Distribution of parasite stages in tissues of Toxoplasma gondii infected SCID mice and human peripheral blood lymphocyte‐transplanted SCID mice

Abstract

The establishment of Toxoplasma gondii infection in the tissues of SCID mice and SCID mice transplanted with human peripheral blood lymphocytes (PBL) was investigated. The presence of bradyzoites and tachyzoites was analysed in hu-PBL SCID mice using Southern blot of reverse transcriptase-polymerase chain reaction products for the expression of B1, BAG1 and SAG1 of T. gondii. BAG1 was present by week 1 in brain, lung, liver and spleen of some animals; by week 3, BAG1 was present in all animals and in all of these tissues. In contrast, SAG1 was rarely detected until week 2 (mainly in the lung and brain) and by week 3, some animals still did not have detectable SAG1 in brain, lung, liver and spleen. SAG1 expression was increased in the lungs of animals transplanted with human PBL compared to nontransplanted SCID mice. Human PBL engraftment was demonstrated, initially in uninfected mice, by the presence of human CD3+ T cells in the spleen (3.1 x 10(5) positive cells) and peritoneal cavity (3.4 x 10(5) cells) 4 weeks after transplantation. The final outcome of infection was not influenced by the presence of human PBL, with similar mortality in human PBL transplanted and nontransplanted mice. These studies provide a detailed analysis of the kinetics and distribution of both the cyst and tachyzoite stage of T. gondii. This system has been established to allow evaluation of therapies against T. gondii immunodeficient mice in the presence of human immune cells.

Human peripheral blood lymphocyte severe combined immunodeficiency (hu‐PBL SCID) models of toxoplasmosis

“…In general, therefore, human PBL were usually detrimental to the host in these studies of IA‐conditioned animals. One possible explanation for this is the fact that the parasite load in transplanted mice is significantly higher in T. gondii ‐infected, conditioned hu‐PBL SCID mice than in conditioned SCID controls 31 . Further studies are currently in progress to determine whether this phenomenon is immunologically mediated.…”

Effect of route of infection on outcome ofToxoplasma gondiiinfection in hu-PBL SCID mice

“…It is therefore likely that this donor had a higher frequency of T. gondiispecifi c lymphocytes. These results were unexpected since in the original model, where cysts were delivered PI, the presence of hu-PBL led to the earlier appearance of mRNA for B1 in the brain and also greater amounts of SAG1 expression in the lung [6,7].…”

“…Although RT-PCR and Southern blotting is a very sensitive method of detection, the amount of tissue analyzed is small (1 μg). The sensitivity of RT-PCR and Southern blotting for parasite detection was found to be 1 bradyzoite by extraction of 1 μg RNA from lysed cysts [7]. In studies of hu-PBL SCID mice 1 μg of total tissue RNA was used for RT-PCR.…”

“…These mice were found to develop a fatal pneumonitis and toxoplasma encephalitis with dissemination of the parasite to multiple sites. Despite the greater severity of disease and parasite load in the lungs of unconditioned hu-PBL-engrafted mice in comparison to non-engrafted animals [7], preliminary analysis of mRNA for human β-actin in the lung, liver, and spleen indicated that human cells were not present in high numbers outside of the peritoneal cavity. It appeared that the IP route of infection may have interfered with the dissemination of the previously engrafted human cells or that the human cells have provided a reservoir of susceptible cells for infection and dissemination of the parasite.…”

“…This was performed by RT-PCR and Southern blotting as previously described [7]. Tissues were snap frozen in liquid nitrogen, homogenized in 1 ml of RNAzol (Tel-Test, Friendswood, TX) and RNA isolated as described by the manufacturer.…”