The photomicrograph shows thymic cortex which has a "starry sky" appearance due to stress involution, characterized by apotosis of cortical thymocytes. Infants undergoing corrective cardiac surgery are under stress due to their underlying cardiac defect as well as due to the stress of hospitalization and surgery. Increased production of corticosteroids as a physiologic response to stress results in apoptosis of cortical thymocytes. These thymocytes are then engulfed and removed by macrophages that reside in the center of the cleared areas (the "stars" in the "sky" of thymic cortex). These macrophages are called "tingible body macrophages" and the cleared areas are called "tingible bodies". An immunoperoxidase stain for CD68, expressed on macrophages, highlights the macrophages (brown color) within the tingible bodies. Apoptotic thymocytes can be visualized in some of the tingible bodies.