Flow cytometric phenotyping of nontransfected (last column on the right) and double transfected K-562 cells. Ectopic LFA-1 cell-surface expression was probed by detection of cell-surface expression of either the CD18 (rows 1–2) or the CD11a (3–4) subunit. Distributions of control and principal single cell fluorescence intensities were obtained after using an isotype-matched non pertinent (filled, grey) or an anti-CD18 or -CD11a primary antibody (open, white) respectively, before detection with Alexa Fluor 488-conjugated secondary Abs. Cells undergoing cell death were defined as those showing PI incorporation (row 5) and their relative proportion was established in mock- (unimodal grey distribution) and ApxIIIA-exposed (uni- or bimodal white) non- or cotransfected K-562 cells. Range of Alexa 488/PI positivity is given in each panel along with percentage of positive cells. See text for details.