"Genetic and Immunohistochemical Analyses of the PD-L1 and PD-L2 Loci and PD-1 Ligand Expression. (A) Location and color labeling of the bacterial artificial chromosome (chr) clones on 9p24.1 used for fluorescent in situ hybridization (FISH). RP11-599H20 including PD-L1, labeled red. RP11-635N21 including PD-L2, labeled green. (B) Representative images of FISH results for the various categories. PD-L1 in red, PD-L2 in green, fused (F) signals in yellow, and centromeric probe in aqua (A). In these images, disomy reflects 2A:2F; polysomy, 3A:3F; copy gain, 3A:6F; and amplification, 15+F. (C) The top panel shows PD-L1 (brown)/PAX5 (red) immunohistochemistry (IHC) in the classical Hodgkin lymphoma cases with 9p24.1 disomy, polysomy, copy gain, and amplification from (B). The bottom panel shows PD-L2 (brown)/pSTAT3 (red) IHC in the same cHL cases. Scale bar = 50 μm.