Figure 5.

Immunohistochemical analysis of EBI3 expression in ATL. a–c: Sections from involved lymph nodes from different ATL patients (all with leukemic form) were stained with anti-EBI3 antibody. a and b: Numerous EBI3-positive neoplastic cells are observed. In contrast, reactive lymphocytes (a, arrows) infiltrating the tumor are negative. In case shown in c, tumoral cells are negative for EBI3, but numerous cells strongly labeled with anti-EBI3 antibodies are observed. Higher magnification (inset) shows that these cells have extended cytoplasmic processes and are morphologically consistent with dendritic cells. d: EBI3 immunostaining in a case of anaplastic large cell lymphoma shows that tumoral cells are negative for EBI3. Staining of a dendritic-appearing cell is observed. e: Double staining for EBI3 (brown) and CD3 (blue) in a nonneoplastic reactive lymph node. Whereas a cell morphologically consistent with a dendritic cell is strongly positive for EBI3 (and CD3-negative), all CD3-positive T cells are negative for EBI3. f: Double staining for EBI3 (brown) and CD8 (blue) in an ATL case (same case as in a) showed that all reactive CD8+ T cells (arrows) surrounding an EBI3+ tumoral cell (arrowhead) are negative for EBI3. Tumoral cells were identified based on their morphology and their immunophenotype including the expression of CD25 (inset: double staining for EBI3 (brown) and CD25 (blue)). In all cases, no signal was observed with control antibodies used in parallel (data not shown). Original magnifications, ×40. Zoom factors: 1 (a); 0.8 (b–d); 1.3 (e–f).