Figure 3.

Citrulline uptake is induced upon T cell stimulation. Primary human CD3⁺ T lymphocytes were isolated from blood of healthy donors by negative selection. (A) Time-dependent uptake of 20 µM [¹⁴C]citrulline into T cells stimulated in the presence of 20 µM arginine for 24 h with anti-CD3/anti-CD28-tagged particles (squares) or left unstimulated (circles). Each data point represents the mean ± SD of three cell aliquots from one blood donor. Comparable results were obtained with cells from two other blood donors. (B) T cells were stimulated with anti-CD3/anti-CD28-tagged particles for 24 h in the presence of the indicated arginine concentrations. Citrulline uptake was then measured after incubation with 20 µM [¹⁴C]citrulline for 30 s. Data represent mean ± SD in percentage of the values obtained with cells from the same donor and stimulated in the presence of 1,000 µM arginine (10.21 ± 8.4 pmol arginine/10⁶ cells, n = 8–9 from three different donors). Statistical calculations were performed with one-way analysis of variance and Tukey’s post hoc test (***p < 0.001).