Activated T cells are capable of 5-HT synthesis. (A) Expression of gene transcripts for SERT, TPH-1, and TPH-2 was determined by RT-PCR from naive T cells and from T cells activated with Con A or PMA plus ionomycin. (B) The relative expression of TPH-1 was quantified by q-PCR. Data are means ± 1 SD (n = 2, P < .001). (C) 5-HT was visualized by confocal microscopy in T cells activated with PMA plus ionomycin by labeling with 5-HT antisera (Alexa Fluor 546; red) (upper left). 5-HT antisera was preabsorbed with 5-HT as the negative control (lower left). Nuclei were counterstained with TO-PRO-3 (blue). Scale bar represents 10 μm. Data are representative of 3 independent experiments. (D) 5-HT concentrations in T-cell culture supernatants were determined by EIA. Data are mean from triplicate assays ± 1 SD (n = 2, *P < .001).