Histopathologic changes of lymph nodes after ALK inactivation by Dox treatment in lymph nodes of TMP3-ALK mice. The architecture of lymph node from mice with fully developed disease (day 0; A-D) is obliterated by lymphoma cells strongly positive for B220 (B). Negative area corresponds to residual T cells as seen in panel C. Lymphoma cells are positive for ALK (D). After Dox treatment (days 2-10: E-P), the lymph node progressively recovers its normal immunoarchitecture together with the decrease of ALK-positive lymphoma cells (H,L,P) and increase in normal B and T cells (M-O). Lymph node from tTA transgenic mice was used as a normal control (Q-T). Original magnification ×50 (A-C), ×40 (E-G,I-K,M-O,Q-S), and ×640 (D,H,L,P,T).