No aggregation occurred in PRP with an inhibition of P-selectin expression during H pylori infection. Stored PRP (24 hours) was preserved in a sealed, air-permeable bag and oscillated in a flat-bottomed shaking device at room temperature. (A) During pro-aggregatory Hp 49503 infection (platelet/bacteria ratio = 25:1), no aggregation was observed in stored Hp IgG⁺ PRP, of which standard agonists (AA, ADP, and collagen) were capable of aggregation. (B) P-selectin expressions were elevated in stored PRP, but there was no significant increase during Hp 49503 infection (platelet/bacteria ratio = 100:1).