Concentration and physiologic effects of soluble CD40 ligand (sCD40L) in supernatants and lysates of platelet concentrates (PCs) associated with ATR(451,715,561,536) and control PCs. (A) Determination of sCD40L levels in PC supernatants and lysates in platelet components associated with ATR versus control components; data obtained from the clinical ATR occurrence with a day-5 (d5) PC sample and a d7 PC sample. (B) PC supernatants and lysates of individual components associated with reactions were tested with purified blood B cells from healthy blood donors stimulated to secrete IL-6; data obtained from the clinical episodes with one d5 and 3 d7 PC samples, respectively. (C) The consistent decrease of IL-6 secretion in response to stimulation with a high concentration of sCD40L in platelet supernatants after preincubation of B cells with 5 μg/mL CD40-blocking antibody. We observed similar results by preincubation of B cells with 5 μg/mL of another CD40-blocking antibody and with both antibodies together (data not shown). All values (pg/mL) were corrected for background levels. Data are expressed as means plus or minus SD in n = 5 experiments. *P < .05 in differences between tested values and respective controls (Wilcoxon paired test).