Gene expression research from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London suggests that there may be more individuals with major depressive disorder (MDD) and activated immune systems than previously estimated. By identifying the molecular mechanisms associated with this connection, the study could lead to improved identification of MDD patients with an immune component, enabling more personalised treatment approaches. The research, funded by the National Institute for Health and Care Research, challenges previous studies focused on inflammation-related proteins like C-reactive protein (CRP) by examining broader immune-related characteristics. The study analysed gene expression in 168 participants, finding increased expression of immune-related genes in those with MDD, even in participants with low CRP levels. These findings highlight the presence of immune activation in depressed patients and support the exploration of targeted interventions for individuals with immune alterations who may not respond well to standard antidepressant medications.