TF antigen on MK is normally masked by terminal sialylation but becomes exposed when sialic acids are depleted (desialylated) or St3gal1 is genetically deleted. pDC-like immune cells sense TF antigen exposure on MKs, which induces IFN-I secretion and inhibits platelet release (left). In the steady state of sialylated O-glycan on MKs, IFN-I secretion is inhibited, possibly via Siglec H, and normal thrombopoiesis occurs (right).