Recently, it has been reported that CD33, which regulates the innate immune system, as well as its gene, has been shown to be a risk factor for AD, CD33 inhibits clearance of Aβ by microglia, and deletion of CD33 in an Alzheimer transgenic mouse significantly reduced pathological amyloid in the brain (Bradshaw et al., 2013; Griciuc et al., 2013). Here, CD33 is linked to Alzheimer disease.