Alzheimer disease (AD) is characterized by the presence of β-amyloid (Aβ) plaques in the brain.1 More evidence of inflammatory parameters, such as, complement factors, proinflammatory cytokines and lymphocytes has been found to be co-localized with Aβ plaques,1,2 The research in the past decades has demonstrated abnormalities of both the humoral and cellular immune responses, suggesting an association of immunological aberration and AD. The total percentage of lymphocytes was not found to be altered, whereas the alterations of T-cell function, differentiation and subset distribution have still been unresolved.3,4 A significantly decreased function of suppressor as well as helper T-cells and natural killer (NK) cells in AD patients has been observed. Studies on lymphocyte subpopulations showed conflicting results, while other studies could not find alterations in lymphocyte subset distribution. In the present study, we assume the immune system dysregulation depending on a defective immune response which also affects lymphocyte differentiation and subset distribution. We investigated T lymphocyte subset pattems and co-stimulatory molecules, as well as B lymphocytes and NK cells in peripheral blood of AD patients and age matched healthy controls.