Alignment of the extracellular domains of PD-L1 and PD-L2. The β strands in mouse PD-L2 are denoted with arrows above the sequence. Red shading, conserved residues; red labeling, residues with similar properties; triangles, residues bearing potential N-glycans; pink, residues conserved between PD-Ls; green, residues conserved for PD-L2 only; green asterisks, residues that contribute to receptor binding of PD-L2; filled circles, residues forming the interdomain hydrogen bonds between PD-L2 IgV and IgC domains.