Figure 3.

ATM expression in thymus. a: Immunostaining of thymus revealed strong expression of ATM in cells of the thymic medulla, but not the cortex. b: Higher magnification of thymic medulla showing that the majority of cells with typical lymphocyte morphology are ATM-positive, whereas in cortex (c) such cells were rarely ATM-positive. Double-labeling of ATM (brown) and CD3 (gray/black; d) confirms the majority of ATM-positive cells in the medulla are T-lymphocytes. Epithelial cells of the thymic medulla were also ATM-positive as evidenced by their co-expression of ATM (brown) and cytokeratin (gray/black; e). f: Epithelial cells of the cortex were also ATM-positive.