CD146, also know as melanoma cell adhesion molecule (MCAM or Mel-CAM), MUC18, S-Endo1, and A32 antigen, is an integral membrane glycoprotein that belongs to the Ig superfamily. CD146 is strongly expressed by murine vascular endothelial cells. It is expressed on about 30% of neutrophils and 60% of NK cells. Unlike in humans, CD146 is undetectable on monocytes, dendritic cells, T cells, NKT cells, B cells, or smooth muscle cells in mouse. It has been reported that an increase in CD146 expression is associated with NK cell maturation. Combined with using CD27 and CD11b staining, CD146 may be an alternative marker to detect final stages of NK cell maturation and define NK cell subsets. CD146+ NK cells were found to be less cytotoxic and to produce less IFNgamma than CD146- NK cells upon stimulation with target cells or activating antibodies. The role of CD146 on NK cell migration has yet to be investigated. The identification of CD146 ligand(s) will be crucial to address this issue.