Histological analysis of thymic transplants. Cryostat sections from thymic grafts of CB/Thy-NOD/SCID mice (a, b, c, g, and h) and control Thy-NOD/SCID mice (d through f) stained by a peroxidase detection method with an anti-human CD45 MoAb (a and d, dark brown color), by 2-color immunofluorescence with an anti-human CD45 MoAb (b and e, green fluorescence), and an anti-mouse MHC class I MoAb (b and e, red fluorescence) or by a TUNEL assay and propidium iodide (c and f, green and red fluorescence, respectively). (g and h) Background staining of isotype control antibodies for the immunohistochemistry and immunofluorescence techniques, respectively. The preservation of cortical and medullary regions (a, cx, and m) in the grafts of CB/Thy-NOD/SCID mice contrast with the perturbed tissue architecture of the grafts from control Thy-NOD/SCID mice (d). Clusters of mouse cells (e, arrows) and numerous apoptotic cells organized in rosette-like clusters (f) can be frequently observed in the grafts of Thy-NOD/SCID mice. In contrast, rare mouse cells (b, arrow) and sparse apoptotic events are observed in the grafts of CB/Thy-NOD/SCID mice (c). Bar in a, d, and g, 254 μm; Bar in b, c, e, and h, 63.5 μm.