ACE2 and severe acute respiratory syndrome: However, the most common models to date for SARS are older BALB/c mice (12–14-month) infected with a virus that been adapted to grow in mice (SARS-MA15) [25] and transgenic mice expressing the SARS-CoV-1 receptor human angiotensin-converting enzyme 2 (ACE2) on a C57BL/6 background (K18-hACE2).