Time course of induction of IL-15 mRNA expression in cord (CB) and adult (APB) MNCs. CB and APB MNCs were isolated, cultured in RPMI, and stimulated with 10 μg/mL LPS for 0, 3, 6, 12, 24, and 48 hours. Cells were harvested and poly (A)⁺ RNA samples were analyzed by Northern blot analysis of IL-15 mRNA (1.5 kb). Results shown are representative of three different CB and APB RNA blot hybridizations, normalized to GAPDH signal. The lower panel bar graph represents comparative IL-15 mRNA expression from LPS-stimulated (12 hours) CB and APB MNCs. Four different CB and APB samples were analyzed after 12 hours of LPS stimulation (10 μg/mL) for IL-15 mRNA expression by Northern blot analysis. The amount of IL-15 mRNA was expressed as a percentage, setting the amount of APB mRNA equal to 100% (APB v CB, 100% v 25% ± 2.0%, P < .05, n = 4).