Figure 2.

Citrulline supplementation preserves the proliferation of CD4⁺ and CD8⁺ T lymphocytes under low arginine concentrations. CD4⁺ (A,C,E,F) and CD8⁺ (B,D,G,H) T cells were isolated from blood of healthy donors by positive selection via paramagnetic bead technology and stimulated and cultured as in Figure 1. (A,B,E,G) T cell proliferation was determined by the incorporation of [³H]thymidine over 16 h (n = 11–18 from 3 to 6 different donors); (C,D,F,H) IFN-γ secretion was detected in T cell supernatants by ELISA (n = 10–21 from 4 to 7 different donors). Data are shown as mean ± SD in percentage of the mean respective value obtained from cells of the same batch and stimulated in the presence of 100 µM arginine [(A) 11,524 ± 8,138 cpm, (B) 11,380 ± 5,223 cpm, (C) 1,234 ± 935 pg/mL IFN-γ, (D) 490 ± 302 pg/mL IFN-γ] or 1,000 µM arginine [denoted as Arg+; (E) 20,736 ± 8,857 cpm, (F) 1,238 ± 676 pg/mL IFN-γ, (G) 7,771 ± 4,304 cpm, (H) 629 ± 467 pg/mL IFN-γ]. Statistical calculations were performed with one-way analysis of variance and Tukey’s post hoc test (***p < 0.001, **p < 0.01, n.s.: p ≥ 0.05). Cit: citrulline; ASA: argininosuccinate.