Cytotoxic effect of IL-4 cytotoxin on human H-RS cell lines. (A) L1236 (○) or HD-MyZ cells (▪, total population; , suspension population; ▴, adherent population) were treated with various concentrations of IL4^38-37-PE38KDEL (0-1000 ng/mL), and protein synthesis inhibition was assessed. Results are presented as mean ± SD of quadruplicate determinations, and the assay was repeated 3 times. (B) Inhibition of HD-MyZ colony formation by IL-4 cytotoxin. HD-MyZ cells (adherent population) were allowed to adhere in Petri dishes and were cultured with various concentrations (0-100 ng/mL) of IL4^38-37-PE38KDEL for 14 days; then colonies consisting of at least 50 cells were scored after staining with crystal violet. Data were obtained from the mean of triplicate determinations. Data are means; bars, SD.