Microscopic findings. (A) Lymph node biopsy revealing lymphocytic proliferation with hypersecretory plasma cells (hematoxylin and eosin [H&E], ×200) or "Mott cells" (box). (B) Gastric biopsy showing lymphoepithelial lesions (arrow) and Mott cells (arrowheads, box; H&E ×100). (C) Immunohistochemical staining for CD20, (D) CD138, (E) kappa and lambda light chains (×400), and (F) pan-cytokeratin (×200).