TNF and major depressive disorder: And the central nervous system is not the only physiological system implicated in depression that probiotics have been shown to influence in rodents: consumption of probiotics reduced levels of the pro-inflammatory cytokines interleukin-1-beta (IL-1β) [24, 32] and interleukin-6 (IL-6), as well as tumor necrosis factor-alpha (TNFα) [24] and microglial activation markers [25], indicating they may possess the ability to reduce overall inflammation.