Intracellular heme oxygenase 1 <t>(HO-1)</t> in primary human tracheo-bronchial epithelial cells 24 h after treatment with sulfur mustard (SM) vapor. HO-1 levels in the medium were measured by western blotting, and normalized to β-actin levels in the same blots following stripping and re-probing. Incubator control (inc ctl): cells maintained in the CO 2 incubator during exposure of the remaining cultures in a glove box. 0: Cells exposed to the vapor from 10 μl of ethanol. SM concentrations are the estimated maximal concentration possible in the vapor phase as the result of the amount present in 10 μl of the dilution applied to the filter.