Representative patterns of response following platelet immunization. Platelet counts (109/L; ○) are shown on the left ordinate and alloantibody (AlloAb; □) and autoantibody (AutoAb; △) responses on the right. Alloantibody responses are expressed as the ratio of the median fluorescence signal obtained postimmunization to the signal obtained with pretreatment plasma using platelets of the immunizing strain as targets in flow cytometry. Autoantibodies are similarly expressed using platelets from the recipient strain as antibody targets. Weeks of immunization are shown on the abscissa. (A) A C57 mouse immunized with PWK platelets produced a strong alloantibody but no detectable autoantibody, and platelets were unaffected. (B) A PWK mouse immunized with 129 platelets produced a strong alloantibody and a moderately strong autoantibody; platelets declined ∼76% from the maximum level. (C) A 129 mouse immunized with PWK platelets produced strong alloantibodies and autoantibodies and experienced a platelet decline of 96%. (D) A 129 mouse immunized with 129 platelets produced neither alloantibodies nor autoantibodies and experienced a platelet decline of 23% from the maximum value.