Effect of citrullination on the in vitro biologic activity in T cells of CXCL10 and CXCL11. (A,C) The chemotactic activity of CXCL10, CXCL10-Cit₅, recombinant (rec) CXCL11, synthetic (synth) CXCL11, and synthetic CXCL11-Cit₆ for PHA-activated T cells was measured using a Boyden microchamber (5-20 independent experiments). Statistical analysis was performed using the Mann-Whitney test on paired values (*P < .05, **P < .01, ***P < .001 for comparison with buffer). (B,D) The increase of [Ca²⁺]_i in PHA-activated T cells was measured on stimulation with CXCL10 (♦) or CXCL10-Cit₅ (□) as shown in panel B or with CXCL11 (♦) or CXCL11-Cit₆ (□) as depicted in panel D. Values represent the mean (± SEM) increase of [Ca²⁺]_i of 3 or more independent experiments with a detection limit at 5 nM (…). Significant differences were calculated using the Mann-Whitney test on paired values (‡P < .05, ‡‡P < .01 for comparison of authentic with citrullinated chemokine). (E) Desensitization experiments were performed by rechallenging the T cells with 1 nM of synthetic CXCL11 100 seconds after the first stimulus. Results (mean ± SEM) represent the percentage inhibition of the second agonist by the first stimulus in comparison with buffer as first stimulus (3-5 independent experiments). Significant differences were calculated using the Mann-Whitney test (‡P < .05 comparison between CXCL11 and CXCL11-Cit₆).