IgM-mediated IL-8–dependent platelet activation.

(A) Washed human platelets from a healthy donor were incubated with 1:10 diluted serum (black bars, 205 μg IgM/mL), isolated total IgM (gridded bars, 35 μg/mL) from P7, or isolated total IgM (gray bars, 35 μg/mL) from the healthy donor as control. Similar results regarding isolated IgM were obtained from 5 experiments with different platelet preparations from the healthy donor (results shown as mean ± SD) or washed platelets from another donor (not shown). (B) Platelets from the healthy donor were incubated with isolated total IgM from P7. Procoagulant activity (gray bars) and annexin V–FITC binding (white bars) were taken as the assay endpoints.