G6b-B–deficient platelets have increased surface IgM and IgG abundance. (A) Whole blood platelet counts from young, 4 to 8 weeks WT, and male and female G6b KO mice were measured. (B-C) Platelets from WT and G6b KO mice were double-stained for GPIbα and either IgM (B) or IgG (C). Flow cytometry analysis revealed that G6b KO mice exhibit higher level of IgM and IgG bound to their platelet surface than WT. Data are means ± SEM. n = 12 per condition.