Generation of a porcine alveolar macrophage cell line for the growth of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has a marked tropism for cells of the monocyte–macrophage lineage and accordingly, replicates in fully differentiated alveolar macrophages in the natural host. Despite the identification of several putative receptors for PRRSV on porcine alveolar macrophages (PAM), only CD163 was found to be able to make non-permissive cells susceptible to PRRSV, indicating a requirement for CD163 in productive infection. Interestingly, the preliminary experiments revealed that the immortalized PAM cell line, which was previously shown to fail to support PRRSV replication, does not express detectable levels of CD163. These data suggest that there may be a correlation between the CD163 undetectable expression level and PRRSV non-susceptibility in the continuous PAM cell line. In this study, therefore, it was attempted to stably transfect non-permissive PAM cells with CD163 cDNA to generate cell lines constitutively expressing CD163 and to evaluate their permissivity to PRRSV. The newly established PAM cell lines were demonstrated to express robust levels of CD163 and to be fully permissive for both type 1 and 2 PRRSV strains. This PRRSV-permissive PAM cell line will be a valuable tool not only to facilitate virus propagation but also to advance in vitro studies on virus pathogenesis.