As sTREM2 is primarily generated by the proteolytic cleavage of the ectodomain and is considered to be identical to the ectodomain of full-length TREM2 in terms of amino acid sequence, we will focus on the ectodomain of TREM2 and the product of its proteolytic cleavage, namely sTREM2, in the molecular mechanisms of AD as well as in the discovery of new therapeutic targets. Here, TREM2 is linked to Alzheimer disease.