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

The establishment of Toxoplasma gondii infection in the tissues of SCID mic e 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. gond ii. BAG1 was present by week 1 in brain, lung, liver and spleen of some ani mals; by week 3, BAG1 was present in all animals and in all of these tissue s. In contrast, SAG1 was rarely detected until week 2 (mainly in the lung a nd 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 mic e. 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 c ells) and peritoneal cavity (3.4 x 10(5) cells) 4 weeks after transplantati on. The final outcome of infection was not influenced by the presence of hu man PBL, wit similar mortality in human PBL transplanted and nontransplante d mice. These studies provide a detailed analysis of the kinetics and distr ibution of both the cyst and tachyzoite stage of T. gondii. This system has been established to allow evaluation of therapies against T. gondii immuno deficient mice in the presence of human immune cells.