Duration of acceptance of single and combined treatments of donor platelet transfusions and donor platelets prepared from MPR-treated WB. (A) Number of weeks that recipient dogs accepted donor platelets that have not been treated (standard; dotted line), PLS-5A F-LR (dash-dot-dot line), PL1B F-LR (dashed line), MPR (solid line), or γ-irradiated (dashed-dotted line). Time to refractoriness was significantly longer for PLS-5A F-LR platelets than for STD and MPR platelets (P ≤ .04), and for all types of platelets than for γ-I platelets (P < .04). Of note, it was 3 weeks before any recipient became refractory to MPR and PL1-B F-LR platelets and 6 weeks to become refractory to PLS-5A F-LR platelets. In contrast, 80% of the recipients of γ-I transfusions became refractory after a single transfusion. Data for STD,²  PLS-5A,⁴  and PL1-B F-LR transfusions⁴  have been previously reported and are given here as reference. (B) Number of weeks that recipient dogs accepted donor platelets was significantly shorter for PL1-B F-LR + γ-I (dotted line) than for either PL1-B F-LR + MPR (solid line) or PLS-5A F-LR + MPR platelets (dash-dot-dot line) (P < .003), and it was significantly shorter for PLS-5A F-LR + γ-I platelets (dashed line) than for PL1-B F-LR + MPR platelets (P = .02) but not for PLS-5A F-LR + MPR platelets (P = .08). There was also no difference between PL1-B F-LR + γ-I and PLS-5A F-LR + γ-I transfusions (P = .48). (C) Number of weeks that recipient dogs accepted donor platelets that were prepared from MPR WB followed by PL1B F-LR of PRP (dashed line) was significantly shorter than than that for platelets prepared from F-LR WB followed by MPR of the WB (solid line) (P = .006). However, even MPR WB + PL1-B F-LR PRP platelets were accepted for at least 4 weeks.