A Rapid Flow Cytometric Method to Explore Cellular Immunity against Toxoplasma gondii in Humans

To assess cell-mediated immunity to Toxoplasma gondii, we evaluated the expression of the activation antigens CD69, CD71, and CD25 on T lymphocytes by flow cytometry after specific in vitro stimulation of whole blood from 127 T. gondii-positive and 63 T. gondii-negative patients. T lymphocytes from many seropositive individuals did not express CD69 at 24 h after T. gondii antigen stimulation, but CD71 and CD25 were easily detectable on T cells from seropositive individuals 7 days after specific activation. CD25 was mainly expressed by stimulated CD4(+) T cells, and its detection on total T cells was both a sensitive (98%) and a specific (97%) indicator of prior T. gondii infection. These results make flow cytometric detection of CD25 an excellent candidate for screening cell-mediated immunity to T. gondii in vitro and an interesting tool for the diagnosis of congenital infection.