Thirty-two children and adolescents with TD (27 males, ages 7–18 years), 17 with comorbid OCD (14 males), and 16 healthy comparison subjects (7 males, ages 9–19), were enrolled. Plasma cytokines were examined using an enzyme-linked immunosorbent assay. The Mann–Whitney and binary logistic regression tests were used to compare the groups.
Only patients with comorbid OCD (TD+OCD; n = 17) had significantly elevated IL-12 plasma levels compared to controls (2.73 ± 5.12 pg/ml vs. 0.55 ± 0.88 pg/ml, rank statistic = 222.5; p < 0.04). IL-2 was significantly higher in the TD+OCD subgroup compared to the non-OCD TD subgroup (0.74 ± 0.29 pg/ml vs. 0.49 ± 0.24 pg/ml, rank statistics = 108.5; p < 0.03). There were no other significant cytokine differences between groups.
Findings suggest a role for IL-12 and IL-2 in TD, and that the TD+OCD subgroup may involve different neuroimmunological functions than the TD−OCD subgroup. Larger studies with medication-free patients should follow.