Unidentified TREM2 ligands were also detected by TREM2-Fc binding to the cell surface of macrophages [252], human astrocytoma cells [244], dendritic cells [253], N2A cells [153, 223], THP-1 cells [223] and apoptotic cells [160]. Here, TREM2 is linked to astrocytoma (excluding glioblastoma).