CD8⁺ T-cell–mediated platelet clearance in immunized B-cell–deficient μMT recipients. (A-B) Serum from nonimmunized μMT (H-2^b) recipients (NI) or FVB (H-2^q)-immunized (I) μMT recipients was incubated with FVB platelets (A) or C57BL/6 (B6) platelets (B) followed by detection of bound antibody by incubation with anti-IgG and flow cytometric examination (n = 5). (C) Serum from nonimmunized or FVB-immunized μMT or C57BL/6 recipients was separated by gel electrophoresis under nonreducing conditions and analyzed by western blot analysis for immunoglobulin as indicated. (D) Nonimmunized or FVB-immunized μMT recipients were transfused with C57BL/6.GFP × FVB (FVB^GFP) or C57BL/6.GFP (B6^GFP) platelets followed by flow cytometric examination 24 hours later (n = 5) (gate = percentage of total platelets). (E-F) Percentage of FVB^GFP (E) or B6^GFP (F) platelets remaining, normalized to nonimmunized recipients as indicated at various time points posttransfusion into nonimmunized (NI) or FVB-immunized (I) μMT recipients (n = 5). (G) Percentage of FVB^GFP platelets remaining, normalized to nonimmunized recipients, at 24 hours following transfusion, as indicated into nonimmunized (NI), FVB-immunized (I), CD8⁺ T-cell (CD8) depleted immunized or NK cell (NK) depleted immunized μMT recipients (n = 4-5). Significance was determined in panels A, B, E, and F by Student t test or by 1-way analysis of variance with the Tukey posttest in panel G (****P ≤ .0001; ns, no significance).