SIGLEC1 and infection: As type I interferons play an important role in the early infection of COVID-19 and CD169/SIGLEC1 is known as a cell surface marker of interferon signaling, we longitudinally analyzed monocytic expression of CD169/SIGLEC1 in reverse transcription polymerase chain reaction (RT-PCR)-confirmed patients with mild and severe COVID-19 in comparison to RT-PCR-confirmed control patients with other diseases.