Further studies [22,23,24,25,26,27,28,29,30] were carried out enabling a meta-analysis [31] (Table 1), which found decreased IL-1β levels and decreased TNFα (tumor necrosis factor α) levels in non-depressed OCD patients (but not in OCD patients with possible comorbid depression), and increased IL-6 levels in adult medication-free OCD patients (but not in OCD children with possible medication use) compared to controls. Here, TNF is linked to major depressive disorder.