SIGLEC1 and infection: However, both ACE2+ (Fig 3C) and CD169/ACE2 double-positive (Fig 3D) THP1/PMA macrophages showed robust dsRNA and SARS-CoV-2 N antigen production starting as early as 2–4 hours post infection (hpi), with substantial increases in N expression over 24 hpi (Fig 3C and 3D).