SIGLEC1 and infection: SARS-CoV-2-infected THP1/PMA macrophages were fixed at various time points post infection and subjected to immunofluorescence analysis using antibodies against dsRNA and SARS-CoV-2 N. In contrast to parental THP1/PMA macrophages that showed background staining of dsRNA and no expression of SARS-CoV-2 N at any time point post infection (Fig 3A), CD169-expressing THP1/PMA cells displayed low levels of dsRNA production and small puncta staining of SARS-CoV-2 N that did not significantly increase over the course of infection (Fig 3B).