KGF is required for thymic reconstitution after sublethal irradiation. KGF^-/-, KGF^+/-, and WT mice were sublethally irradiated (450 cGy), and mice were harvested at day 21 and at day 28 after irradiation. (A-B) Thymic cellularity was determined, and DP, DN, CD4⁺, and CD8⁺ thymocyte numbers were calculated by flow cytometric analysis and thymic counts. (C) Splenic cellularity was determined, and splenic CD3⁺CD4⁺, and CD3⁺CD8⁺ T-cell numbers were calculated by flow cytometric analysis and splenic counts. (D-F) Peripheral blood was obtained from these mice at different time points, and white blood cell (WBC) counts, platelet counts, and hemoglobin levels were determined by an automated cell counter. Values represent mean (± SEM) and n = 3-10 per group. ^*P < .05.