As with ketamine and fasting, it is possible that the association between increased IL-6 and reduced depression in response to WBH might reflect the ability of IL-6 to induce anti-inflammatory cytokines with neurotrophic properties, in particular IL-4, which promotes stress resilience, neurogenesis, and protection against the damaging effects of central nervous system inflammation [38–44]. Here, IL4 is linked to major depressive disorder.