TNF and major depressive disorder: In conclusion, results from this study suggest a hitherto unrecognized relationship between hyperthermia, the immune system, and depression, and may point to WBH as a potential modality for exploring behavioral effects of IL-6 in isolation from the inflammatory mediators (e.g., TNF, IL-1-beta) that activate the cytokine in the context of acute infection or in response to the triggers for chronic inflammation (e.g., obesity, sedentary lifestyle) that are all too common in the modern world.