Expression of Foxn1 in postnatal thymus. (A) Cryostat sections of 4-week-old wild-type thymus stained for Foxn1 and either MHCII (i-iv), or UEA-1 (v-viii). MHCII^hi and UEA-1^hi cells were associated with bright Foxn1 signals (arrowheads). Scale bar in subpanel iii: 50 μm, applies to subpanels i through iii and v through vii. (iv,viii) Higher magnification views of the boxes in subpanels iii and vii showing colocalization of Foxn1 (nuclear) and MHCII or UEA-1. (B) Loss of Foxn1^hi (lacZ^hi) TECs in aged thymus. X-gal staining on frozen sections of Foxn1^+/lacZ thymi at 3 weeks, 6 weeks, 7 months, and 12 months. Eosin counterstaining (pink) is lighter in aged thymus due to lower T-cell density.