Proteomic analysis of the secretome of porcine alveolar macrophages infected with porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes porcine reproductive and respiratory syndrome (PRRS), which is characterized by reproductive failure and respiratory disorders. The secretome of PRRSV-infected porcine alveolar macrophages (PAMs), which are the primary target cells of PRRSV, was analyzed by label-free quantitative proteomics to gain a profile of proteins secreted during PRRSV infection. A total of 95 secreted proteins with differentially expressed levels between PRRSV- and mock-infected PAMs was screened. Among these, the expression levels of 49 and 46 proteins were up-regulated and down-regulated, respectively, in PRRSV-infected cell supernatants, as compared with mock-infected cell supernatants. Bioinformatic analysis revealed that the differentially expressed proteins were enriched in several signaling pathways related to the immune and inflammatory responses, such as the Toll-like receptor signaling pathway and NF-kappa B signaling pathway, and involved in a great diversity of biological processes, such as protein binding and localization, as well as immune effector processes. In addition, PRRSV-infected cell supernatants induced significant expression of inflammatory cytokines in vascular endothelial cells. These findings suggest that the secreted proteins play potential roles in the host immune and inflammatory responses as well as PRRSV replication, thereby providing new insights into cell-to-cell communication during PRRSV infection.