PROS1 and infection: The exposed position of the RBD enables binding to the angiotensin converting enzyme 2 (ACE2) receptor24 and, as a result, it is the main target of anti-SARS antibodies during infection.25, 26, 27, 28, 29, 30 Due to this phenomenon, combined with its high recombinant protein yields, several antibody tests have been developed using RBD as a tool to test for previous SARS-CoV-2 infection.31, 32, 33, 34 One disadvantage of using RBD as an antigenic bait for testing is that it may not capture the entire antibody response to the S protein as it lacks the full trimeric structure.35