Recombinant Mouse TREM2 Fc Chimera Protein, CF

TREM-2 (Triggering Receptor Expressed on Myeloid cells-2) is a type I transmembrane member of the TREM family and Ig superfamily (1, 2). Mouse TREM-2 cDNA encodes 227 amino acids (aa) that include an 18 aa signal sequence, a 153 aa extracellular domain (ECD) with one V-type Ig-like domain, a 21 aa transmembrane (TM) domain, and a 35 aa cytoplasmic tail (1). A soluble, 249 aa form of TREM-2 (TREM-2b) created by alternate splicing diverges at aa 161 (1-3). Within aa 19-161, mouse TREM-2b shares 73%, 88%, 73% and 71% aa sequence identity with the human, rat, bovine and equine TREM-2 ECD, respectively. In both TREM-1 and TREM-2, a positively charged lysine within the TM domain allows association and signaling through the signal adapter protein, DAP12 (1, 2). While TREM-1 induces macrophage activation, TREM-2 coupled with the linker protein LAT2 is inhibitory (5-7). TREM-2 is detected on newly differentiated and alternatively activated tissue macrophages, immature myeloid dendritic cells and osteoclasts, but not on circulating or tissue-resident myeloid cells (2, 6, 7). It is active in several settings that involve membrane fusion, including phagocytosis of microbes by macrophages and apoptotic neurons by microglia, and formation of osteoclasts and multinucleated giant cells from macrophages (2, 4, 8-11). TREM-2 is also interacts with and modifies signaling through dendritic cell and osteoclast Plexin A1, a semaphorin receptor (12). Mutations in human TREM-2 or DAP12 can result in Nasu-Hakola disease (NHD), also called PLOSL (polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy; 2, 11, 13). NHD patients show presenile dementia and bone cysts, presumably due to persistence of apoptotic neurons and faulty osteoclast development (2, 11, 13). Soluble TREM-2 antagonizes full-length TREM-2 and is elevated in cerebrospinal fluid of patients with active multiple sclerosis, and blockade of full-length TREM-2 exacerbates the mouse multiple sclerosis model, EAE (2, 4, 14).