SEB induction of CD40L expression in PBMCs. PBMCs were plated in the presence and absence of SEB or plate-bound α-CD3 and soluble α-CD28 antibodies for 6 hours and stained for CD4 and CD40L expression. The CD4⁺ lymphocyte gate is shown. The data from stimulated cells (black open histograms) are overlaid on that from unstimulated cells (grey filled histograms). The percentage of CD40L⁺ CD4⁺ cells is indicated. Data is representative of 3 independent donors.