TNF and Alzheimer disease: Importantly, studies investigating the correlation between cytokine levels and occurrence of AD have reported the presence of cytokines TNF-α and IL-1β in cerebrospinal fluid (Tarkowski et al., 2003), and elevated plasma levels of cytokines IL-1β and IL-6 (Licastro et al., 2000) in patients, which suggests their active role in the pathophysiology of AD.