TREM2 and Alzheimer disease: TREM2 is a cell surface receptor of the immunoglobulin superfamily expressed on various cells of the myeloid linage including CNS microglia, bone osteoclasts, alveolar and peritoneal macrophages [25] According to neuropathology studies in AD patients, animal models and in vitro studies, the TREM2 R47H variant induces a partial loss of function of TREM2, compromising microglia function and thus contributing to the development of AD.