Malignant HRS cells and reactive cells from primary HL tumors express BAFF and APRIL. (A) BAFF, APRIL, CD30L, and CD40L on HRS cell lines. Open and shaded profiles correspond to antibody under study and control antibody with irrelevant binding activity, respectively. (B) The top 3 panels show BAFF, APRIL, and β-actin transcripts, while the bottom 3 panels show BAFF, APRIL, and actin proteins in HRS cell lines. Numbers indicate HD-MyZ (1), HD-LM2 (2), L428 (3), KMH-2 (4), and L1236 (5) HRS cell lines. Minus (−) indicates negative control (no cDNA); plus (+), positive control (cDNA from IARC100 lymphoblastoid cell line). (C) BAFF and APRIL in CD30⁺ HRS cells from a classical HL tumor. DAPI (blue) stains nuclei, arrowheads point to reactive CD30⁻ cells surrounding CD30⁺ HRS cells, and asterisks indicate representative CD30⁺ HRS cells. Original magnification ×40. Panel C shows 1 of 15 cases yielding similar results.