Expression of PD-L1 occurs on MCs in MCL. Splenic tissue from a patient with MCL was stained for MCs (tryptase, red), PD-L1 (light green), and nuclei (DAPI, blue). (A) Image acquired at ×20 magnification. Scale bars, 100 µm. Note the MC nest localized around the PALS. (B) Image acquired at ×63 magnification. Scale bars, 20 µm. White boxes in overlay image denote the region magnified in the right column. The coexpression of PD-L1 and tryptase in MCs is demonstrated at high power, however, only a subset of MCs is positive for PD-L1. Smaller numbers of PD-L1⁺ cells lacking tryptase coexpression are also seen at the edge of MC infiltrates.