TPO stimulates aggregation of platelets in a subpopulation of donors.

Aggregation of gel-filtered platelets was monitored by light transmission where a decrease in optical density (OD) reflects aggregation. (i) Platelets from approximately 1 in 5 donors were found to undergo aggregation in response to TPO (50 ng/mL). (ii) Wortmannin (Wt) preincubated 15 minutes before the addition of TPO was found to completely block aggregation. The aggregation trace is representative of 4 experiments.