Cytokines can travel through the bloodstream and lymphatic system to reach the brain and influence mental function.

“there's a class of molecules called cyto kindes and cyto kindes are basically the signaling hormones of the immune system and they they can flow through the bloodstream and through lymphatic fluid uh and reach many parts of the body uh we've known for a number of years that the specialized receptors for these cyto kindes are found throughout the brain and yet we know very very very little about about what they do and that's going to be an astonishingly fruitful area of scientific research”