Porcine reproductive and respiratory syndrome virus (PRRSV) may persist in tissues of pigs for months. How the virus persists in certain pigs remains to be determined. It is possible that a subset of white blood cells trap the virus and allow it to remain in host tissues undetected by the immune system. We have provided the first isolation and characterization of a specific type of white blood (called a dendritic cell) in the lung of pigs which may play a role in early contact with PRRSV. These tissue-derived cells were distinct compared to similar cells derived in the laboratory. Our data indicates that lung cells are less susceptible to viral infection that the in vitro derived cells. We next sought to determine whether we could track the trafficking of cells to the othe tissue in the body using the dye carboxyfluorescein diacetate succinimidyl ester (CFSE). We were unable to detect labeled cells in the tissues. The use of other appropriate dyes should be considered.