ALO is heavily infiltrated with leukemic T cells in a zebrafish model of T-ALL. (A–F) Fluorescence images of Tg(lck:EGFP)^cz2 wild-type sibling (A, C, and D) or T-ALL HLK^dz102 mutant (B, E, and F) adult animals. Panels show overview images of the ALO/pectoral area taken with a fluorescent stereomicroscope (A and B), confocal images of most of the ALO (C and E), and higher magnification confocal images of the ALO cortex and underlying medulla (D and F). The images in panels D and F correspond to the boxed regions in panels C and E, respectively. The image in panel A was taken with 4× higher exposure and 3× higher gain than the image in panel B, because this area was much brighter in the T-ALL fish than in the wild-type fish. (G–J) H&&E-stained paraffin histological sections of ALOs from adult wild-type (G and H also shown in Fig. 2 F) or T-ALL HLK^dz102 mutant (I and J) adult animals. The images in panels H and J correspond to the boxed regions in panels G and I, respectively. The T-ALL HLK^dz102 ALO is almost entirely filled with leukemic T cells. Transgenic imaging, n = 6; histology, n = 3. Scale bars = 1 mm (A and B), 100 µm (C and E), 25 µm (D, F, G, and I).