(A) Double staining of CD20 (red) and cyclin D3 (brown) in a case of MCL. Lymphoma cells exhibit a B-cell phenotype with red membrane staining for CD20, whereas the nuclei are negative for cyclin D3. By contrast there are a number of cyclin-D3–positive brown labeled nuclei in the periphery of the tumor nodule, most probably belonging to reactive T cells that are CD20 negative. (A) Double staining of CD45R0 (red) and cyclin D3 (brown) in a case of MCL shows that most of the cyclin-D3–positive cells within this tumor display simultaneously T-cell properties (arrow). (C) Double staining of CD20 (red) and cyclin D3 (brown) in a lymphoma of MALT. There are few cells labeled for cyclin D3 in their nuclei. These cells also exhibit CD20 staining with one double labeled cell within the epithelium of a gastric gland (arrow). (D) Double staining of CD20 (red) and cyclin D3 (brown) of a large B-cell lymphoma. There are a number of cyclin-D3–positive cycling cells that also show CD20 expression.