SIGLEC1 and viral infectious disease: It has also been demonstrated that pigs lacking sialoadhesin (Sn/Siglec-1/CD169) (the host macrophage protein that GP5 interacts with) are permissive to PRRSV infection, while pigs lacking CD163 (the host protein in which the GP2-GP3-GP4 complex interacts with) are completely resistant to virus infection (57, 58).