KGF treatment restores thymopoiesis in aged mice. The thymic cellularity of young (6 weeks old, n = 5) and aged mice (15 months old, n = 5-11) was analyzed 1 to 3 months after a single 3-day course of PBS or KGF treatment. (A) Mean absolute thymocyte numbers ± SD from either PBS- or KGF-treated young and aged mice. *P < .05, PBS versus KGF; †P < .05, 1 month versus 2 months; ‡P < .05, 2 months versus 3 months; NS indicates not significant. ⊡ indicates PBS-treated mice; □, KGF-treated mice. (B) Increases in the number of TN, DP, SP CD4, and SP CD8 thymic subsets 1 month after KGF treatment. The fold increase of the number of thymocyte subsets is shown in parenthesis. *P < .05, PBS versus KGF.