Pathological findings of lymph nodes in ATLL with HTLV-1–infected HRS-like cells and abnormal medium-sized lymphoid cells. (A) In the lymph nodes of case 4, HRS-like cells were surrounded by relatively monotonous medium-sized lymphoid cells with mild nuclear atypia (hematoxylin and eosin staining). (B-C) The HRS-like cells were positive for CD30 (B) and CD15 (C). (D-F) The medium-sized lymphoid cells were positive for CD3 (D) and CD4 (E) but lacked CD7 expression (F), indicating an abnormal T-cell phenotype. (G-H) Both the HRS-like cells and the medium-sized lymphoid cells were positive for CD25 (G), whereas only the medium-sized lymphoid cells were diffusely positive for CCR4 (H). (I) HBZ-ISH revealed that both HRS-like cells and medium-sized lymphoid cells were infected with HTLV-1. Arrow indicates an HRS-like cell. Original magnification ×400 (A-I).