Expression of HLA-B8, HLA-B12, and HLA-B35 on PLTs varies significantly between individuals. Specific HLA class I expression on PLTs was determined using Alexa Flour 488–labeled mAbs that specifically target HLA-B8 (A), HLA-B12 (B), or HLA-B35 (C). For each donor, relative median fluorescence intensities were averaged and are represented by 1 circle. Donors were sorted based on their expression levels. Staining from donors negative for the specific HLA allele is depicted by a dotted line (mean) and gray area (mean ± 2 SDs).