Opsonization of PLTs with low HLA-B8, -B12, or -B35 expression does not lead to antibody-mediated internalization by macrophages. PLTs with low (n = 7), intermediate (n = 4), or high (n = 9) HLA-B8, -B12, or -B35 expression were left unopsonized or opsonized with anti-HLA-B8, anti-HLA-B12, or anti-HLA-B35, and internalization by macrophages was determined (A). Positive controls were opsonized with anti-HPA1a (B). Antibody-mediated internalization was correlated with antigen expression using a Pearson correlation test (C). Intracellular fluorescence was normalized against unopsonized PLTs from the same individual and presented as mean (A,C) or mean ± SEM (B). Statistical differences in internalization were determined using a Wilcoxon matched-pair test (A, unopsonized vs low/high) or Mann-Whitney U test (A, high vs low; B). Statistical significance is depicted as **P < .01, ***P < .001.