Thymic histology. Hemotoxylin and eosin stains of the thymus of 3 representative animals at necropsy 12 to 14 months after transplantation. Thymus (left panel) scored as grade 1: well-preserved architecture with well-defined cortex and medulla, no atrophic changes. Grade 2 thymus (middle panel): some degree of atrophic changes consisting of fat replacement of lobules and preservation of cortex and medulla and islets of cell-dense tissue containing many thymocytes. Grade 3 thymus (right panel): marked atrophic changes and cystic degeneration. All photos were taken with an Olympus BX41 microscope, objective 4 × /0.13 UPlanFl.