Fig. 4

Platelet activation by anti-CD40 ligand (anti-CD40L)antibodies requires FcγRIIa interaction. a In vitro platelet aggregation isolated from humans. Preformed immune complex (IC) (anti-CD40L antibodies plus soluble CD40 ligand (sCD40L)) was incubated with isolated platelets from four human volunteers; representative data from one volunteer are shown. Traces show the percentage of platelet aggregation over a 6-minute time period from one donor, but is representative of four donors. b In vitro dense granule release from human platelets. Anti-CD40L antibodies (final concentration 500 nM, with/without sCD40L) were incubated with isolated human platelets (n = 4), and ¹⁴C-radiolabeled serotonin release was measured. Data are plotted as mean percentage serotonin release (average of the means of four donors (SRA)). Error bars are standard deviation for the mean percentage SRA values of the four donors. c In vitro platelet aggregation isolated from Rhesus monkeys. Preformed IC was incubated with isolated platelets from two Rhesus monkeys (RH1 and RH2). Traces show the percentage of platelet aggregation over a 6-minute time period from one donor, but is representative of two donors. d In vitro dense granule release from Rhesus monkey platelets. Preformed IC or antibody solutions (final concentrations 500 nM) were incubated with isolated platelets from four Rhesus monkeys (black bars) or one healthy human donor (gray bars), and ¹⁴C-radiolabeled serotonin release was measured. Thrombin receptor agonist peptide (TRAP) (100 μM) was included as a positive control. Data are plotted as in b.