CRP and major depressive disorder: This could be particularly relevant in view of the secondary results from an RCT with add-on treatment with Infliximab, a tumour necrosis factor (TNF)-alpha-antagonist, in patients with treatment resistant depression; in the exploratory ‘post-hoc’ stratification analyses of this study, the authors found that only patients with higher levels of C-reactive protein (CRP > 5 mg/L) showed improvement with Infliximab, while placebo was superior to Infliximab in improving depressive symptoms in those with CRP levels equal/below the identified threshold of 5 mg/L [21].