Flow cytometric quantification of Toxoplasma gondii cellular infection andreplication

The invasion and replication of Toxoplasma gondii are usually analyzed thro ugh either optical microscopy or incorporation of tritiated uracil. A new m ethod has been developed using flow cytometric analysis to examine the entr y and replication of T. gondii RH strain in Saimiri brain endothelial cells . After cell fixation and permeabilization using saponin, intracellular T. gondii were labeled with a monoclonal antibody against T. gondii SAG-1 (P30 ; the major cell-surface antigen) followed by fluorescein-conjugated rabbit anti-mouse IgG. The percentage of infected cells obtained using flow cytom etry correlated directly with that obtained by UV light microscopy (r = 0.9 7). The mean fluorescence intensity of infected cells reflects intracellula r P30 and assesses intracellular replication. The distribution of fluoresce nce per infected cell, considered with the percentage of infected cells, al so allows a qualitative analysis of replication. Such a method is rapid, ea sy, and does not require specialized equipment for radioactive labeling.