Figure 3.

Thymic stromal PR is required for thymic involution. (A) Immunoperoxidase staining for PR in untreated wild-type and PRKO mouse thymus. Staining was found almost exclusively in large cells of the medullary region. (B) Photographs of wild-type- and PRKO-transplanted thymuses after 12 days of E + P treatment or pregnancy demonstrate a requirement for stromal PR in thymic involution. Ruler demarcated in millimeters. (C) Transplant thymic histology after E + P or pregnancy. Five micrometers H&E-stained sections of transplanted wild-type and PRKO thymuses taken from wild-type mice after pregnancy. Notice the relative loss of cortical lymphocytes in the wild-type pregnant thymus, whereas the thymus containing PRKO stroma appears intact. Bar = 100 μm.