Effects of IL-2 supplementation on the activities in GCS, SMS, and acid and neutral SMases. KHYG-1 cells were cultured in the absence (○, IL-2^-) or presence of IL-2 supplementation (100 U/mL) after 12 hours of deprivation (•, IL-2^-→+). The cells were harvested at indicated times (0, 12, 24, and 36 hours), and after extraction of the proteins the activity of each enzyme was assessed. The activities of GCS (A), SMS (B), acid (C), and neutral (D) SMases were measured by using C6-NBD-ceramide and C6-NBD-SM as the substrates as described in “Materials and methods.” The activities of each enzyme detected in IL-2-supplied control cells were 789 ± 66, 41 ± 1.6, 579 ± 25, and 917 ± 91 pmol/mg protein/hour for GCS, SMS, acid, and neutral SMases, respectively. The bars indicate 1 SD. The significance of differences of enzyme activities was determined by ANOVA test. ^*P < .01; ^**P < .05; #P > .05.