CD33 and Alzheimer disease: CD33 is a transmembrane receptor principally expressed on both haematopoietic and phagocytic cells, including monocytes, dendritic cells and microglial cells, suggesting its significant role in immune responses.1 Although the precise role of CD33 in human physiology remains elusive, it has been shown in several studies to be involved in the pathogenesis of Alzheimer’s disease.