Effector/memory but not naive CD4⁺ T cells from unmanipulated animals mobilize preformed CD40L. CD40L expression in naive and effector/memory CD4⁺ T cells from unmanipulated normal (A-C), CD40-deficient (D-F), and CD40L-deficient (G-I) animals was analyzed by conventional surface staining (A,D,G), intracellular staining (B,E,H), and the surface mobilization assay (C,F,I). (A,B,D, E,G,H) The levels of CD40L (shaded) and isotype control (line) staining for the indicated population of CD4⁺ T cells are shown. (C,F,I) Shaded indicates CD40L with stimulation. –– indicates CD40L without stimulation. –– indicates isotype control with stimulation. ------ indicates isotype control without stimulation. Data shown are representative of 4 independent experiments.