Treatment-resistant depression affects tens of millions worldwide, and the unexplained speed of ketamine's antidepressant action — often within hours — has puzzled researchers for years. If psychedelics and ketamine, which bind entirely different receptors, achieve similar rapid relief through a shared downstream mechanism, that convergence point could become a precise therapeutic target and a biomarker for predicting who will respond.
A multimodal study published in Molecular Psychiatry combined cerebrospinal fluid proteomics from healthy volunteers receiving intravenous ketamine with transcriptomic data from induced pluripotent stem cell-derived neurons treated with ketamine, its active metabolite (2R,6R)-hydroxynorketamine, LSD, and psilocybin. Across these distinct compounds and data modalities, two immune signaling proteins emerged as convergent hubs: interleukin-15 (IL-15) and monocyte chemoattractant protein-1 (MCP-1). In treatment-resistant depression patients who responded to a single 0.5 mg/kg IV ketamine infusion, whole-blood transcriptomics showed suppressed IL-15 and heightened B-cell pathway activity at baseline — a profile that reversed following treatment. Critically, plasma IL-7 levels, a primary B-cell growth factor, correlated significantly with baseline magnetoencephalography gamma-band power across all participants, surviving false-discovery-rate correction brain-wide.
This finding sits at the intersection of two rapidly evolving fields: neuroimmunology and psychedelic medicine. The idea that immune signaling — particularly cytokine-driven lymphocyte activity — modulates rapid antidepressant response challenges the dominant monoamine and glutamate-centric frameworks. IL-15 is well established in NK-cell and T-cell homeostasis, but its role in depression neurobiology is far less characterized, making this an intriguing lead. The MEG-plasma correlation linking peripheral IL-7 to cortical oscillatory dynamics is particularly compelling as a potential non-invasive biomarker strategy. Limitations are significant: the iPSC model, while mechanistically informative, remains several steps removed from in-vivo human brain pharmacology, and cohort sizes in the transcriptomic arm are modest. Still, the multimodal convergence across cerebrospinal fluid, blood, neurons, and brain imaging elevates this beyond routine hypothesis generation — it is a potentially paradigm-shifting repositioning of neuroimmune pathways as primary mediators of rapid antidepressant action.