CAECs were stimulated with or without TRAIL and then incubated with O2−· -specific spin trap 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) to form more stable free radicals (CMH-O2−·), which was immediately analyzed by electron spin resonance spectrometry (ESR). Summarized data showing the effect of TRAIL on O2−· production in Smpd1+/+ and Smpd1−/− CAECs., *P < 0.05 vs. Smpd1+/+ control; #P < 0.05 vs. Smpd1+/+ TRAIL (n=6).