Impaired in vitro lymphocyte response to toxoplasma antigen in HIV1 infected patients.

The containment of Toxoplasma gondii infection is largely dependent of T cell mediated immunity. In this study, in vitro lymphocyte responsiveness to T. gondii antigen was examined in 59 HIV1 infected individuals and in 58 HIV non-infected controls. Of the 45 patients with serological evidence of past Toxoplasma infection, a significant proliferative response was found in only 18, whereas responses were present in 48 out of 51 controls with anti-Toxoplasma antibodies. In the 27 non-responder patients, the lack of proliferative response to T. gondii antigen was correlated with the loss of CD4+ cells, and the impairment of proliferative responses to other microbial antigens, whereas responsiveness to phytohaemagglutinin and concanavalin A were not significantly diminished. Results are consistent with impairment of cell mediated immunity to T. gondii in patients at risk for reactivation of chronic Toxoplasma infection. Of note, in the one year clinical following, 2 of the 27 non-responder patients developed toxoplasmic encephalitis compared to 0 of 18 with a Toxoplasma specific proliferative response.