Disorganized thymic microenvironment in aged Smad4^{co/co;Foxn1Cre} mice. Immunofluorescence analysis of thymi from neonatal (A,B), 6-week- (C,D), and 20-week-old mice (E,F) with a Smad4^co/co (A,C,E) or Smad4^{co/co;Foxn1Cre} (B,D,F) genotype stained for cytokeratin 5 (red) and cytokeratin 18 (green). Hematoxylin and eosin staining of thymi from 20-week-old Smad4^co/co (G) or Smad4^{co/co;Foxn1Cre} (H) mice. Detailed analysis of a cyst stained either (I) with cytokeratin 5 (green), cytokeratin 18 (red), and DAPI (white), or (J) with cytokeratin 5 (red), cytokeratin 18 (green), and ERTR7 (blue). Scale bars represent 100 μm.