CD30L expression and detection of apoptotic cells in fetal and postfetal human thymuses. (A) Large numbers of cytokeratin-positive cells (bluish-grey color) in a fetal thymus specimen taken at week 11 of gestation (original magnification ×100). (B) Absence of TE4 and (C) absence of CD30L immunostaining (bluish-grey color) in the same fetal thymus (original magnification ×100). (D) Large numbers of cytokeratin-positive cells (bluish-grey color) in a fetal thymus taken at week 13 of gestation (original magnification ×400). (E) Several cells in a adjacent section staining positive for TE4 (bluish-grey color original magnification ×400). (F) A few cells in an adjacent section showing CD30L immunoreactivity (bluish-grey color, original magnification ×400). (G) Apoptotic cells detected by the TUNEL technique (red color) in a postnatal fetal thymus (original magnification ×100). (H) Absence of apoptotic cells in a fetal thymus taken at week 11 of gestation (original magnification ×100).