Anti-CD44 inhibits FcγR-mediated platelet clearance according to anti-GPIIb/IIIa IgG subclass in murine ITP. Passive antibody-mediated ITP was induced in C57BL/6 mice via IV tail vein injection using IgG1 anti-GPIIb/IIIa (clone MWReg30), which mediates thrombocytopenia through FcγRIII (A), or IgG2a anti-GPIIb/IIIa (clone 5C4), which mediates thrombocytopenia through FcγRs but is not dependent on FcγRIII (B). Anti-CD44 (α-CD44) or isotype control was administered IV by tail vein injection 30 minutes before anti-platelet antibody injection. Platelet counts were determined at 24 hours after anti-platelet antibody administration. Data are from 6 (A) or 7 (B) independent experiments with 1 mouse per experiment. Error: mean ± standard error of the mean (SEM). ****P < .0001, 1-way analysis of variance with Tukey’s post hoc test.