A link between elevated blood IL-6 levels and depression is well established in both patients (Dowlati et al. 2010; Haapakoski et al. 2015; Nobis et al. 2020) and rodent models (Krishna et al. 2016; Rodrigues et al. 2018; Wickens et al. 2018) with IL-6−/− mice being resistant to induced depression-like behaviour (Chourbaji et al. 2006; Monje et al. 2011). This evidence concerns the gene IL6 and depressive symptom measurement.