Human β5t is expressed exclusively in the thymic cortex. (A) Hematoxylin and eosin (HE) staining of neonatal human thymic tissues. (B,C) Immunofluorescence staining of neonatal human thymic tissues. The medulla is identified by the presence of Hassall corpuscles and lower cell density than in the cortex. β5t-expressing cells are located only in the cortex, and most of the β5t-expressing cells in the cortex are keratin-positive cTECs. Magnified images of immunostaining (C) reveal that β5t is expressed in cTECs, but some β5t-expressing cells are not stained with the Ab for keratins (arrow). The staining patterns shown were representative of three neonatal thymic tissues. Negative control (NC) was stained with normal rabbit serum and mouse IgG1. (D) HE and immunofluorescence staining of adult human thymus. Expression of β5t is maintained in cTECs. The staining patterns shown were representative of five adult thymic tissues. Red represents β5t; green, keratin. Bar indicates 100 μM.