WIP KO mice evolve platelet-associated IgAs. (A) WT, WASp KO, and WIP KO platelets were incubated with Alexa Fluor 488–labeled donkey anti–mouse immunoglobulin antibody (open) or anti–rabbit immunoglobulin antibody (shaded) as negative control. (B) WT and WIP KO platelets were incubated with a nonimmune goat IgG or goat antibodies directed against mouse Ig classes as described, followed by Alexa Fluor 488–labeled donkey anti–goat IgG antibody. Results are ratio between mean fluorescence obtained with specific and unspecific antibodies and represent the mean ± SE of 4 to 6 mice per group. Box plot of platelet-associated (C) and plasma (D) IgA levels from WT and WIP KO littermates, as determined by isotype-specific ELISA. NS indicates not significant.