GP1BA and Thrombocytopenia: Administration of recombinant IL-1 to mice resulted in the cell cycle activation of Vwf+ and Vwf- HSCs (Fig. 3d), with Vwf+ HSCs being recruited at a higher extent into the S-G2-M phase of cell cycle (Supplementary Fig. 4e), compatible with IL-1 mediating the HSC activation in response to anti-GPIbα-induced thrombocytopenia.