COVID-19 and platelets: an enigmatic relationship

Coronavirus disease 2019 (COVID-19) is a life-threatening infectious disease that was first identified in the Chinese city of Wuhan at the end of 2019. Since then, the disease has spread worldwide, making it one of the 10 deadliest pandemics in recorded human history. Although COVID-19 is essentially a respiratory disease, as the virus mainly colonizes and replicates in the cells of the upper and lower respiratory tract, under certain circumstances the disease can also affect cells in other tissues and organs, thus assuming the specific characteristics of a systemic disease. Soon after the emergence of the first severe COVID-19 cases, it became clear that platelets play an essential role in the pathogenesis of SARS-CoV-2 infection, whether as bystanders or active players. This chapter therefore aims to provide up-to-date information on the phenotypic interplay between COVID-19 and platelets in patients with SARS-CoV-2 infection.