Naive and memory cells both express CD40L early and late. (A) CD40L expression in stimulated, reconstituted PBMC cultures of pure CD45RA⁺ or CD45RO⁺ CD4⁺ T cells from a single donor. (B) Early- and late-phase CD40L expression in reconstituted PBMCs from 13 donors. Due to overlap of the data points, not all symbols are visible. Solid bars indicate the mean. (C) Umbilical cord blood mononuclear cells were stimulated ± anti-CD25 mAb. The means ± SE of 4 donors are shown.