Anti–IL-7Rα antibody treatment does not impair donor-derived thymopoiesis following allogeneic BMT. Both histologic features and donor-derived cell analysis of the thymus from recipient mice were analyzed at day 30 after BMT. Shown are representative thymuses from normal, PBS-treated congenic BM, PBS-treated allogeneic BM, PBS-treated allogeneic BMT-plus-LN, and anti–IL-7Rα antibody-treated allogeneic BMT-plus-LN-cell recipient mice. (A) Similar to normal and BMT-only recipients, the thymus from anti–IL-7Rα–treated allogeneic BMT and LN-cell recipients shows sharp demarcation between cortical (dense blue areas) and medullary (less dense blue areas) regions in H&E staining. Conversely, atrophic thymus from PBS-treated allogeneic BMT-plus-LN recipients displayed disorganized boundaries between cortex and medulla. (B) Thymic tissue sections from recipients receiving transplants were stained with FITC-conjugated anti-K8 (green) and PE-conjugated anti-K5 (red) antibodies to characterize the cortical (K5⁻ K8⁺) and medullary (K5⁺ K8⁻) TECs. (C) Representative FACS analyses of CD4 and CD8 expression by donor-derived thymocytes at day 30 after BMT. (D) The number of donor-derived thymocytes in BMT recipients at day 30. The difference between PBS- and anti–IL-7Rα–treated allogeneic recipients is P < .05 (asterisk). See “Materials and methods, Histologic analyses” for image acquisition information.