TARGETED DISRUPTION OF THE GRA2 LOCUS IN TOXOPLASMA-GONDII DECREASES ACUTE VIRULENCE IN MICE

Following invasion into the host cell, the protozoan Toxoplasma gondii secretes a variety of proteins that modify the parasitophorous vacuol e, Within the vacuole, the 28-kDa dense granule protein known as GRA2 is specifically targeted to the tubulovesicular network which forms co nnections with the vacuolar membrane, To investigate the importance of GRA2, we derived from strain RN a mutant T.gondii line in which GRA2 was disrupted by replacement with the marker Ble (selecting for phleom ycin resistance). The Delta gra2 mutant invaded and grew normally in b oth fibroblasts and macrophages in vitro; however, it was less virulen t during acute infection in mice. The survival rate? of mice inoculate d with Delta gra2 was significantly higher; some infected mice survive d the acute infection, whereas all mice infected with the wild-type st rain RH succumbed to early death. Chronic infection by Delta gra2 was detected by positive serology, immunohistochemical detection of parasi tes and cysts in the brain, and reisolation of parasites by bioassay a t 6 weeks postinfection. Thus, absence of GRA2 partially attenuates th e virulence of T. gondii during the acute phase of infection and allow s for establishment of chronic infection by the otherwise highly virul ent RH strain. These results establish that GRA2 plays an important ro le during in vivo infection and provide a potential model for examinin g acute pathogenesis by T. gondii.