TNF and Alzheimer disease: While some studies have found increased levels of TNF-alpha in patients with AD,24 25 some have found decreased levels26 27 and others have found no difference.28 Studies investigating TNF-alpha levels at different stages of disease have in general found higher levels of TNF-alpha in patients with severe AD compared with mild AD and MCI,29 30 and therefore it may be that the increase in TNF-alpha is seen at a later stage in disease than other cytokines.