CD30L expression by Hassal's corpuscles and medullary TEC in postnatal thymus. (A) CD30L immunoreactivity in the thymic medulla. Section was immunostained with anti-CD30L MoAb, using the avidin-biotin-peroxidase method, and the AEC substrate (red color, original magnification ×100). (B) CD30L immunoreactivity (red color), which is clearly visible in a medullary area (bottom right), limited to a few scattered cells in the cortex (original magnification ×100). (C) Strong CD30L immunoreactivity in the outer part of a Hassal's corpuscle (original magnification ×1,000). (D) CD30L immunoreactivity in some medullary cells (original magnification ×250). (E) Double immunostaining for CD30L and cytokeratin in the medullary area. CD30L was identified by using the AEC substrate (red color) and cytokeratin by using the Vector SG substrate (bluish-grey color). Hassal's corpuscles and some cells staining for both cytokeratin and CD30L (purple-brown color), as well as many cells staining for cytokeratin alone, are visible (original magnification ×400). (F) Double immunostaining for CD30L (red color) and TE4 (bluish-grey color). Cells staining for both CD30L and TE4 (purple-brown color), as well as cells staining for TE4 alone, are visible (original magnification ×400). (G) Absence of immunostaining in a thymic medullary section where the anti-CD30L Ab was replaced by an isotype-matched control MoAb (original magnification ×400). (H) Double immunostaining showing distinct cellular distribution for CD30 (red color, arrows) and CD30L (bluish-grey color, arrowheads, original magnification ×1,000).