Immunolabeling for B-cell–associated signaling molecules in classical Hodgkin disease. All staining was performed on paraffin biopsies by immunoperoxidase or double immunofluorescent techniques. (A) Left: Reed-Sternberg cells are negative for Lyn kinase (white arrows), which is confined to reactive lymphocytes. A single Reed-Sternberg cell that shows cell-membrane–associated staining is seen in the inset. Right: Double immunofluorescent staining in an exceptional case of mixed cellularity disease (no. 17 in Table 1) in which Lyn was expressed (CD30, red; Lyn, green) confirms that this kinase is present in Reed-Sternberg cells. (B) Left: Heterogeneous immunostaining for Fyn in Reed-Sternberg cells in a case of mixed cellularity (no. 16 in Table 1), comprising both positive (black arrows) and negative tumor cells (white arrow). The inset shows clear cytoplasmic staining in a multinucleated Reed-Sternberg cell. Right: Double immunofluorescent labeling for CD15 (green) and Fyn (red) confirms the expression of Fyn by Reed-Sternberg cells. (C) Left: Reed-Sternberg cells (white arrows) and accompanying T cells are Syk negative, contrasting with Syk-positive reactive B cells. The inset shows a Syk-negative multinucleated Reed-Sternberg cell. Right: Reed-Sternberg cells are consistently BLNK negative (white arrows), as highlighted in the insets, contrasting with positive-reactive B cells. (D) Left and right: Reed-Sternberg cells are PLC-γ2 negative (white arrows), as highlighted in the insets. Reactive B cells are strongly PLC-γ2 positive. Original magnifications: × 20 (C, right panel), × 40 (A, left panel; B, left panel; C, left panel and right panel insets; and D), and × 60 (A, left panel inset and right panels; B, left panel inset and right panels; and C, left panel inset).