Scavenger receptor CD163 and sialic-acid binding lectin CD169 were identified as key receptor molecules for Porcine Reproductive and Respiratory Syndrome Virus (PRRSV),an important arterivirus which replicates in porcine myeloid cells expressing the above.Porcine alveolar macrophages (PAMs) are generally used for propagating virus,but being primary tissue cells are difficult to obtain,vary in susceptibility and are thus rather unreliable.CD14+ monocytes are considered unsuitable for PRRSV infection,but initial experiments in our laboratory showed that at least some monocytes could propagate PRRSV.