Histopathology and immunohistochemistry of Mll-AF4 mice with leukemia or lymphoma. (A) Spleen section from a representative Mll-AF4 mouse with lymphoma stained with H&E and shown at low magnification demonstrates loss of normal architecture resulting from follicular B-cell lymphoma. Bar represents 200 μm. (B) The same spleen section is shown at high magnification. Bar represents 50 μm. (C) Liver section indicates B220⁺ lymphoma cell infiltration. Bar represents 50 μm. (D) Liver section from the same specimen shows Bcl-6⁺ lymphoma. Bar represents 50 μm. (E) Spleen section shows PAX5⁺ lymphoma cells. Bar represents 50 μm. (F) Small intestine section shows IgM⁺ lymphoma cells. Bar represents 50 μm. (G) Spleen section from an Mll-AF4 mouse with MPD-like myeloid leukemia stained with H&E indicates loss of normal architecture and heavy infiltration of myeloid cells at all stage of maturation. Bar represents 50 μm. (H) Spleen section from a Mll-AF4 mouse with MPD-like myeloid leukemia stained with myeloperoxidase. Bar represents 50 μm. (I) IgH rearrangements in the spleen and lymph nodes of an Mll-AF4 mouse with follicular B-cell lymphoma. Lane 1, spleen from a wild-type mouse; lane 2, kidney from the same wild-type mouse; lane 3, spleen from an Mll-AF4 mouse; lane 4, lymph node from the same mouse. gDNA was digested by EcoRI. Germline band, 6.5 kb; additional band in lane 2 and lane 3, 7.5 kb.