**2.1 Angiotensin-converting enzyme 2 receptor interaction**

Angiotensin-converting enzyme 2 (ACE2) has been identified as a functional receptor for coronaviruses [6]. The ACE2 receptor is present throughout multiple cellular organs such as the heart, kidney, lungs, as well as in the central and peripheral nervous system [9]. As with other respiratory viruses, respiratory tract symptoms are the most common. The gradient of receptor expression has been directly correlated with the ability of SARS-CoV-2 to infect cells throughout the respiratory tract. The highest concentration of ACE2 receptors is found in the hair cells of the nasal mucosa and is 80% lower in trachea, bronchi and lung tissue [10]. SARS-CoV-2 binds to the transmembrane ACE2 protein to enter type II pneumocytes; due to this tropism, SARS-CoV-2 can interact with a large area of the pulmonary microvasculature. In addition, it can infect pericytes and perivascular cells on the surface of microvessels. ACE2 receptor expression on endothelial cells increases their vulnerability to SARS-CoV-2 binding, causing infection and subsequent vascular injury, dysfunction and endotheliitis [6]. Likewise, interaction with ACE2 receptors in the peripheral nervous system may contribute to the development of myopathies and neuropathies [9].
