Lymph node biopsy specimens of cHD and ALCL.

(A-D) Paraffin-embedded sections immunostained for Notch1 and counterstained with hematoxylin. HRS cells (A, B; arrows) with bilobed or multilobed nuclei, huge inclusionlike nucleoli, and abundant cytoplasm and (C) large pleomorphic cells with prominent nucleoli, ALCL tumor cells, are intensely labeled by anti-Notch1 antibodies. Bystander cells and reactive lymphoid tissue (D) show low to undetectable immunoreactivity levels against Notch1. (E, G) Immunostaining for Jagged1. Jagged1 is expressed in HRS cells (E, arrows) and in tumor cells of ALCL (G). (F) Radioactive in situ hybridization of a case of cHD with probes specific for Jagged1. Endothelial and smooth muscle cells show abundant Jagged1 mRNA expression (arrow). Original magnification × 200 (A-C), × 100 (D), × 200 (E-G).