Immunohistochemical staining of PD-L1 and PD-1 in mastocytosis. Immunohistochemical expression of PD-L1 is shown at left for (A) MCL, (C) smoldering SM, (E) ISM, (G) SM-AHN (MDS/MPN), and (I) CM. At right, immunohistochemical staining for PD-1 is shown for (B) MCL, (D) smoldering SM, (F) ISM, and (J) CM. (G-H) In SM-AHN (MDS/MPN), the PD-L1 expression is restricted to the MC component as shown in panel G, but it is not present in the associated hematologic neoplasm as shown in panel H. Magnification ×40 in panels A-D,I-J and ×20 in panel E-H. Images taken with an Olympus BX41 microscope with Olympus cellSens standard version 1.14 software, and standard color balancing and image sizing using Adobe Photoshop.