GPIbα deficiency leads to a significant decrease in platelet-mediated hepatic TPO generation. TPO mRNA was measured via RT-qPCR (A) and TPO protein was measured by ELISA (B) (n = 6-10) in WT BALB/c and GPIbα^−/− hepatic tissue lysates. (C) Plasma TPO levels were measured by ELISA at the indicated time points following transfusion of 2.5 × 10⁸ WT BALB/c or GPIbα^−/− platelets into GPIbα^−/− recipient mice. Values are normalized to TPO levels on day 0 (100%) (n = 6-12). (D) TPO mRNA levels in liver of GPIbα^−/− mice, as measured by RT-qPCR, 24 hours following transfusion of 2.5 × 10⁸ platelets (n = 5). *P < .05, **P < .01. NS, not significant.