Susceptibility of BoCD11a/PoCD18-expressing human erythroleukemic K-562 cells to ApxIIIA is dose-dependent. Transfected cells with similar LFA-1 expression rates were first incubated for 1 h with decreasing concentrations of ApxIIIA and then analysed for PI incorporation by flow cytometry. ApxIIIA induced concentration-dependent cell death (grey boxes) while culture medium (RPMI-1640) did not (negative control, black). Values are means ± SD from triplicates. Asterisks point to concentrations causing significantly higher cytotoxicity than that spontaneously recorded from mock-exposed double transfectants (P < 0.05).