Possible chemokine gradient produced by platelets in spiral arteries and its estimated effects on trophoblast infiltration toward the arteries. In spiral arteries that are undergoing vascular remodeling, platelets and ECM are deposited among the endovascular trophoblasts. These platelets are likely to have been activated by trophoblasts or ECM and to have released various soluble factors including CCR1 ligands to form a local chemokine gradient around the remodeling spiral arteries. These processes may encourage further trophoblastic arterial infiltration and thus contribute to physiological vascular remodeling during human early pregnancy, providing a positive feedback cascade.