Comparison of cell toxicity at comparable levels of immunotoxin binding.

Tac-TGN38 and Tac-furin cells were treated with the indicated dose of LMB-2. After a 24 hour incubation with immunotoxin, cells were washed, and the cells remaining in the well were used for A) Hoechst-based cell count assay or B) LDH assay as described in Methods. Panels A and B show the relative cytotoxicity plotted against the amount of LMB-2 adjusted to reflect the different Tac expression levels (Figure 3C) in the cell lines ([LMB-2] × Tac expression). Here the cytotoxicity has been normalized so that a value of 1 represents the maximum killing observed with the highest dose of LMB-2 for each cell line (relative cytotoxicity). The data points represent the cytotoxicity values averaged over several experiments, cell count assay (n = 9), LDH assay (n = 8). The standard error of the mean is shown.