KGF administration enhances thymopoiesis in young and middleaged normal mice. Normal 3-month-old CBA mice received 5 mg/kg KGF or PBS subcutaneously on 3 consecutive days. Mice were harvested at different time points after KGF administration, and thymic and splenic cellularity were determined. (A) Thymic cellularity at days 1, 4, 7, 14, and 28 after KGF administration in young mice. Dotted gray line represents normal number of thymocytes (3-month-old CBA). (B) Splenic CD3⁺ T-cell numbers at days 4, 7, 14, and 28 after KGF administration in young mice. (C-H) Thymic cellularity and the number of thymocyte subsets were determined at days 4 and 7 after the final administration of KGF. Thymocytes were stained, and subpopulation numbers were calculated as described in Figure 1. Values represent mean (± SEM) and n = 4-8 per group. ^*P < .05.