Recombinant Mouse CD99-L2 Fc Chimera Protein, CF

CD99 antigen-like 2 (CD99-L2) is a 45 kDa type I transmembrane glycoprotein in the CD99 family of molecules (1 - 3). Mouse CD99-L2 cDNA encodes a 214 amino acid (aa) precursor with a 23 aa predicted signal sequence, a 116 aa extracellular domain (ECD), a 21 aa transmembrane segment, and a 54 aa cytoplasmic region (4). The ECD contains no N-linked glycosylation sites, but O-linked glycosylation is likely (1, 2). A long isoform with a 23 aa insert after aa 43 within the ECD is expressed in human, and probably in mouse (2, 5). Both long and short isoforms may have minor variants missing portions of the N-terminus of the mature protein (6). The ECD of mouse CD99-L2 short isoform shares 85%, 72% and 66% aa identity with rat, human, and bovine CD99-L2, respectively (3, 5). The mouse CD99 and CD99-L2 ECDs share only 31% aa identity, but both contain three conserved acidic motifs and are thought to originate from the same ancestral gene (1, 2). The nearly ubiquitous expression of CD99-L2 is similar to that of CD99. Mouse CD99-L2 shows highest in situ hybridization signals in neurons, cortical thymocytes, ganglia, ovarian granulosa cells, testis, and kidney, and detectable protein levels in lung, thymocytes, mouse leukocytes and vascular endothelial cells (2, 7). CD99-L2 expression on endothelial cells is reported to mediate cell aggregation and neutrophil or monocyte extravasation to inflamed tissue in vivo, while CD99 mediates lymphocyte extravasation as well (3, 7).