PF4 and pulmonary arterial hypertension: It has also been shown that the gradual hypoxia caused by the early onset of PAH will further lead to the activation of platelets, forming a vicious circle that again exacerbates the condition of patients with PAH, while the depletion of platelets is able to reduce the generation of chemokines, such as CXCL4 and CCL5, and slow down the progression of the disease (32).