Tetrahydrobiopterin is perhaps the most overlooked and seldom mentioned critical nutrient in the body. When overly reliant upon cell-mediated immunity, e.g., to kill cancer or the flu virus, the proliferative lymphokines, Interleukin-2 (L-2) and interferron-gamma (IF-gamma), actually cause Neopterin to be produced instead of biopterin, When this happens, not only are we at risk from death from cytokine (lymphokine) storm, but we are also unable to make enough neurotransmitters to carry on basic function like “think”. This is particularly problematic with the body's use of tryptophan for making serotonin and melatonin. When one doesn't have apple pectin in ones diet and energy (GTP) to make hormones, one makes carcinogenic kynurenine and formate.