T cells express the enzyme for 5-HT synthesis and T-cell 5-HT is sequestered by BMDCs. (A) Expression of TPH-1 and TPH-2 was determined by RT-PCR in naive T cells, Con A- (5 μg/mL) activated T cells, and Con A-activated T cells rested for 4 days in IL-2 (10 μg/mL). Comparable quantities of cDNA were ensured by amplification of GAPDH. Data are representative of 2 experiments. (B) BMDC uptake of [³H]5-HT from T-cell supernatants at 0°C, room temperature, and room temperature with fluoxetine (100 nM). Freshly purified, naive T cells were loaded with 1 μM [³H]5-HT (1 hour, 37°C). Cells were washed and resuspended in HBSS (1 hour, 37°C) to passively release [³H]5-HT. BMDCs were resuspended in T-cell supernatant (2 hours, room temperature). Data are means ± SD (n = 2; ^*P < .001,t test).