Single-cell RNA sequencing reveals immune response dynamics and infection mechanisms in PRRSV-infected porcine...

Porcine reproductive and respiratory syndrome virus (PRRSV) gives rise to late-term abortions and stillbirths in sows, and respiratory disease in piglets, causing enormous economic losses to the global swine industry during the last three decades. Here, we revealed the transcriptional heterogeneity of PRRSV-infected PAMs in vitro by single-cell RNA sequencing (scRNA-seq) analysis and provided a detailed and thorough account of the immune response exhibited by host cells during PRRSV infection. In the early stage of infection, the process of ER-mediated phagocytosis plays a crucial role in viral entry. Numerous phagocytosis-promoting receptors, including Fc receptors, were significantly upregulated. By neutralizing the CD16 receptor, one of the Fc receptors on PAMs, we observed a significant decrease in the number of PRRSV-infected cells, suggesting that the CD16 receptor is involved in viral infection. As the infection progresses, the PRRSV-N protein accumulate progressively, resulting in a notable activation of cellular apoptosis and the TNF signaling pathway. Meanwhile, macrophages with the highest levels of viral N protein expression exhibited the greatest cellular activity and interacted with other cells via the ligand-receptor protein complex SPP1-CD44. Upon addition of exogenous SPP1 protein, we observed a significant reduction in PRRSV replication within PAMs, indicating that SPP1 has the ability to inhibit viral infection. These findings uncovered new insights into the immune responses of PAMs, highlighting a previously unrecognized mechanism for PRRSV-induced pathological effects, which may aid in developing therapeutic options for PRRSV-associated diseases.