MyD-1 coupling to PI 3-kinase and sphingosine kinase is maturation dependent. U937 cells (A-B) or U937 cells induced to differentiate toward a macrophage phenotype by culture with dibutyrl cAMP (1 mM) for 48 hours (C-D) were stimulated in the presence (filled symbols) or absence (open symbols) of anti-MyD-1 (10 μg/mL) for the indicated times and PIP₃ (A,C) or sphingosine-1-phosphate (B,D) measured as described in “Materials and methods.”