**The 40 kDa Linear Polyethylenimine Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection by Blocking Its Attachment to Permissive Cells**

**Jie Wang 1,2,**†**, Jie Li 1,2,**†**, Nana Wang 1,2, Qi Ji 1,2, Mingshuo Li 1,2, Yuchen Nan 1,2, En-Min Zhou 1,2, Yanjin Zhang <sup>3</sup> and Chunyan Wu 1,2,\***


Received: 26 July 2019; Accepted: 17 September 2019; Published: 19 September 2019

**Abstract:** Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating infectious diseases in pigs worldwide. The causative agent is the PRRS virus (PRRSV). In this study, we explored polyethylenimine (PEI), a cationic polymer with different forms (linear or branched), to inhibit the replication of PRRSV. Our results demonstrate that the linear but not the 40 kDa branched PEI, or the 25 kDa linear PEI, were well tolerated in cultured cells and exhibited a broad-spectrum inhibition of heterogeneous *PRRSV-2* isolates in both MARC-145 cells and primary porcine pulmonary alveolar macrophages (PAMs). Further analysis suggests that PEI could prevent the attachment of PRRSV virions to the susceptible cells. Notably, PEI had a minimal effect on PRRSV internalization in MARC-145 cells, whereas PEI promoted the internalization of PRRSV virions in PAMs, which suggests that these two types of cells might have different internalization processes of PRRSV virions. In conclusion, our data demonstrate that PEI could be used as a novel inhibitor against PRRSV.

**Keywords:** PRRSV; polyethylenimine; PEI; virion internalization; antiviral; endocytosis
