During recent symptomatic toxoplasmosis, alterations in quantity and function of mononuclear cellsin peripheral blood were observed. Flow cytofluorometric analysis and differential leukocyte counts revealed increasedabsolute numbers of T8 + cells, Leu 7 + (natural killer/killer) cells, and monocytes. T4+ cells and HLA-DR+ cells were not significantly changed. T4/T8 cell ratios were reversed in symptomatic toxoplasmosis (0.7 ± 0.3) and normal in chronic infection (1.7 ± 0.5). Toxoplasma antigen induced higher numbers of T8 + and TQ1 + cells in four T cell lines from two individuals with symptomatic infection than in five T cell lines from three individuals with asymptomatic infection. Eight cloned T cell lines produced γ interferon in an antigen-specific fashion and in higher amounts when they originated from an asymptomatic subject than from a symptomatic subject. These results indicate that marked alterations in properties of immunoregulatory cells are characteristic of recent symptomatic toxoplasmosis. The transient immune dysfunction may be a major part of the observed disease and/or a feature of successful parasitis
