Antibody-producing donor B cells associate with thymus damage in cGVHD recipients. HCT was carried out with BALB/c recipients as described in Figure 1. (A) Analysis of CD4⁺CD8⁺ double-positive thymocytes at 40 and 60 days after HCT. Staining profiles representative of 4 replicate experiments are shown, Means ± SE are displayed for percentage and yield of double-positive thymocytes at 40 and 60 days after HCT. (B) On days 40 and 60 after HCT, BALB/C recipient thymus cell suspensions were measured for the percentage of mTECs. Gated thymic epithelial cells (TECs) are shown as UEA I (medullary TEC [mTEC] marker) vs Ly51 (cortical TEC marker). A flow cytometry pattern representative of 4 replicate experiments is shown. Means ± SE (N = 4) of the percentage of mTECs are shown. (C) On day 40 after HCT, thymus sections were analyzed by histoimmunofluorescent staining for cytokeratin 8 (red, cortical epithelial cells) and UEA-I (green, mTEC). Photomicrographs (original magnification, ×100) representative of 4 replicate experiments are shown. (D) On day 40 after HCT, thymus sections were evaluated by histoimmunofluorescent staining with anti-mouse IgG-FITC (green) and 4,6 diamidino-2-phenylindole (DAPI) (blue, nucleus). Photomicrographs (original magnification, ×100) representative of 4 replicate experiments are shown (**P < .01, ***P < .001, ****P < .0001).