Cytotoxic T-Lymphocyte-Mediated Lysis of Toxoplasma gondii-Infected Target Cells Does Not Lead to Death of Intracellular Parasites

CD8(+) T cells play a crucial role in the control of infection with intracellular microbes. The mechanisms underlying the CD8(+) T-cell-mediated clearance of the intracellular pathogen Toxoplasma gondii are, however, not completely understood. The effect of CD8(+) cytotoxic T-lymphocyte (CTL)-mediated lysis of host cells on the viability of intracellular T. gondii was investigated. Quantitative competitive PCR of the gene encoding T. gondii major surface antigen (SAG-1) was combined with treatment of the parasites with DNase, which removed the DNA template of nonviable parasites. The induction by CD8(+) CTLs of apoptosis in cells infected with T. gondii did not result in the reduction of live parasites, indicating that intracellular T. gondii remains alive after lysis of host cells by CTLs.