Histologic analysis of spleen and lymph node. Spleens from WT (A [× 100] and C [× 400]) and KO (B [× 100] and D [× 400]) show expanded red pulp in the KO animals with increased extramedullary hematopoiesis (note megakaryocytes) and hemosiderin deposition. Lymph nodes from WT (E) and KO (F-H) show expansion of pale staining plasma cells expanding the medullary cords (F) or in patches in the interfollicular zones (G) of the nodes at × 100. At higher power (× 1000, H), histologically normal plasma cells are identifiable by their coarse chromatin, perinuclear Hof, and cytoplasmic immunoglobulin inclusions (Russel bodies). Tissue was paraffin embedded and sections were stained with hematoxylin and eosin. Photomicrographs were taken on an Olympus BXS1 microscope (Olympus, Melville, NY) with UPlanFl 10 ×/0.30 and 40 ×/0.75 objectives using an RT Slider camera and SPOT software (Diagnostic Instruments, Sterling Heights, MI).