ACE2 and infection: As of August 17, 2020, the US Food and Drug Administration (FDA) approved use of 37 serological assays12 mainly targeting two immunogenic proteins: the spike (S) protein,1 the most exposed viral protein, and the nucleocapsid (N) protein,2 which is expressed abundantly during infection.13, 14, 15 The S protein is responsible for binding and entry of the virus into the host cell via the cellular receptor angiotensin-converting enzyme 2 (ACE2).16