Immunohistochemical detection of FN (A) and VCAM-1 (B) in human thymus. Frozen sections of human thymus were labeled with anti-FN MoAb (FN-15) or a mixture of anti-VCAM-1 MoAbs (1G11 and 4B9) and the results developed by immunoperoxidase staining. (C) Is the staining with a negative control antibody. The cortex (C), corticomedullary junction (CMJ), and medulla (M) are marked in each panel. In (A), the majority of FN staining is apparent in the medulla and connective tissue septa crossing the cortex to the subcapsular region (arrow). In contrast, (B) shows that the majority of VCAM-1 staining is evident in irregularly shaped islands of cells in the cortex and corticomedullary junction (left arrow). Nonetheless, a number of isolated VCAM-1 positive cells are also seen in the medulla (right arrow).