In comparing the effects of sulfur mustard (SM)-induced cell death in adult cultured normal human epidermal keratinocytes (NHEK) and peripheral blood lymphocytes (PBL), we observed an SM concentration-and time-dependent loss of NHEK and PBL viability as measured by propidium iodide exclusion. By this parameter alone, PBL appeared more susceptible to SM-induced cytotoxi-city than NHEK, as previously reported. However, therewas a concentration-and time-dependent loss of NHEK yield that was not observed in PBL. Keratinocyte yield was approximately 46% and 8% of control cells at 12 and 24 hours, respectively, following exposure to 0.3 mM SM. The decrease in NHEK yield was associated with an increase in trypan blue-stained fragments observed on slides. Fragments were not observed on slides of SM-exposed PBL cultures. These results suggest that SM causes fragmentation of cultured NHEK and subsequently results in a lower cell yield. The fragmented dead NHEK are not included in the total cell count when percent viability is determined by propidium iodide exclusion. Therefore, cytotoxicity of SM in NHEK is greater than that reflected by dye exclusion alone. Actual viable cell count, which considers both propidium iodide exclusion and cellyield, indicates NHEK are more susceptible than PBL to SM-induced cytotoxicity, contrary to previously published reports. Cell yield must be taken into account when using in vitro models to study not only viability, but also any quantitative biochemical changes induced by SM.
