Programmed death ligand 2 (PD-L2), also named B7DC and butyrophilin-like protein, is a member of the B7 family of proteins that provide signals for regulating T cell activation and tolerance. Other family members include B7-1, B7-2, B7-H2, B7-H1 (PD-L1), and B7-H3. B7 proteins are immunoglobulin (Ig) superfamily members with extracellular V-type Ig-like and C-type Ig-like domains and short cytoplasmic domains. Among the family members, they share 20 - 40% amino acid sequence identity. The extracellular domains of mouse and human PD-L2 share approximately 72% amino acid sequence identity