Transcriptional Immune Signatures of Alveolar Macrophages and the Impact of the NLRP3 Inflammasome on Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Replication.

Julie A Hicks,Dongwan Yoo,Hsiao-Ching Liu

doi:10.3390/v12111299

Abstract

Porcine Reproductive and Respiratory Syndrome (PRRS) is a contagious viral (PRRSV) disease in pigs characterized by poor reproductive health, increased mortality, and reductions in growth rates. PRRSV is known to implement immuno-antagonistic mechanisms to evade detection and mute host responses to infection. To better understand the cellular immunosignature of PRRSV we have undertaken transcriptome and immunomodulatory studies in PRRSV-infected porcine alveolar macrophages (PAMs). We first used genome-wide transcriptome profiling (RNA-seq) to elucidate PRRSV-induced changes in the PAM transcriptome in response to infection. We found a number of cellular networks were altered by PRRSV infection, including many associated with innate immunity, such as, the NLRP3 inflammasome. To further explore the role(s) of innate immune networks in PRRSV-infected PAMs, we used an NLRP3-specific inhibitor, MCC950, to identify the potential functionality of the inflammasome during PRRSV replication. We found that PRRSV does quickly induce expression of inflammasome-associated genes in PAMs. Treatment of PAMs with MCC950 suggests NLRP3 inflammasome activation negatively impacts viral replication. Treatment of PAMs with cell culture supernatants from macrophages subjected to NLRP3 inflammasome activation (via polyinosinic-polycytidylic acid (poly I:C) transfection), prior to PRRSV infection resulted in significantly reduced viral RNA levels compared to PAMs treated with cell culture supernatants from macrophages subjected to NLRP3 inflammasome inhibition (MCC950 treatment/poly I:C transfection). This further supports a role for NLRP3 inflammasome activation in the innate macrophagic anti-PRRSV immune response and suggests that PRRSV is sensitive to the effects of NLRP3 inflammasome activity. Taken together, these transcriptome and immunoregulatory data highlight the complex changes PRRSV infection induces in the molecular immune networks of its cellular host.

Highlights

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a highly contagious ss (+)RNA virus, which is not currently well controlled by vaccines and other preventative strategies [1].As such, PRRS-associated economic losses, including reproductive failure, piglet loss, and treatment measures, cost the swine industry millions of dollars annually [2]
Ingenuity Pathway Analysis (IPA) of these differentially expressed genes found that multiple canonical immune pathways are altered in PRRSV-infected macrophages
We found that PRRSV RNA levels, concerning both VR-2332 and Ingelvac-MLV, were significantly (p < 0.05) lower in porcine alveolar macrophages (PAMs) treated with cell culture supernatants from NLRP3 inflammasome activated

Summary

Introduction

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a highly contagious ss (+)RNA virus, which is not currently well controlled by vaccines and other preventative strategies [1].As such, PRRS-associated economic losses, including reproductive failure, piglet loss, and treatment measures, cost the swine industry millions of dollars annually [2]. Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a highly contagious ss (+). RNA virus, which is not currently well controlled by vaccines and other preventative strategies [1]. A major roadblock to current PRRS vaccination and disease prevention strategies is PRRSV’s ability to both evade and directly antagonize the host’s immune response upon infection. Upon PRRSV infection, only a weak immunological response is mounted during the first days and weeks post-infection, which results in both a Viruses 2020, 12, 1299; doi:10.3390/v12111299 www.mdpi.com/journal/viruses. Available vaccines often display the same delayed immunogenicity as field isolates and typically only provide protection against genetically-related viral strains [3]. There are several commercially available PRRSV vaccines. Among them, is the modified live virus vaccine Ingelvac MLV produced by Boehringer

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