Innate Antiviral Cytokine Response to Swine Influenza Virus by Swine Respiratory Epithelial Cells

Chicken intestinal organoids reveal polarity-dependent replication dynamics and immune responses of low pathogenic avian influenza viruses

Low pathogenic avian influenza viruses (LPAIVs) persist in poultry populations, posing an ongoing challenge to poultry management and research. These viruses typically cause mild infections but can lead to significant economic losses due to their widespread presence and potential to disrupt poultry production. Traditional in vivo and in vitro models struggle to accurately replicate the avian intestinal environment, where these viruses often establish infection. In Taiwan, the domestic H6N1 LPAIVs cause an endemic in the local area but still lack investigation. This study addresses this gap by utilizing advanced chicken intestinal organoid (CIO) systems, apical-out (Ap-o), and basal-out (Ba-o) conformations to study the unique replication kinetics and innate immune responses of LPAIVs in a physiologically relevant setting. By comparing the Taiwan specialized H6N1 strain toward the Eurasian H9N2 virus, our results demonstrate that Ap-o organoids, which mimic natural exposure to the intestinal lumen, elicit robust interferon-stimulated gene responses, particularly higher expression of downstream gene, which effectively controls viral replication against H6N1 virus. In contrast, Ba-o organoids, representing a systemic infection route, exhibited lower upstream interferon responses, reflecting a different immune response pattern in the H9N2 strain. These results confirm that CIO is a well-suited model to study LPAIV pathogenesis. It provides key insights into the host-pathogen interactions that determine viral replication and immune evasion strategies. This model deepens our understanding of LPAIV behavior in poultry and provides a valuable tool for developing more targeted and effective control strategies for poultry health management.

Chicken hnRNPK suppresses interferon production, thereby enhancing IBDV replication

Heterogeneous ribonucleoprotein K (hnRNPK) is a well-known RNA-binding protein initially identified for its role in inhibiting the growth of various human tumors. Members of the hnRNP family have also been implicated in both interferon production and RNA virus replication. However, the role of chicken hnRNPK (chhnRNPK) in the replication of Infectious Bursal Disease Virus (IBDV) remains unclear. In this study, we identified chhnRNPK as a protein that interacts with genomic double-stranded RNA (dsRNA). Following IBDV infection, chhnRNPK was recruited to the virus replication complex in the cytoplasm. Furthermore, chhnRNPK expression inhibited dsRNA-induced interferon production, specifically at the mitochondrial antiviral signaling protein (MAVS) step. Overexpression of chhnRNPK significantly enhanced virus replication, while knockdown of chhnRNPK increased dsRNA-induced interferon production and subsequently disrupted IBDV replication. Collectively, these findings suggest that chhnRNPK promotes IBDV replication by interacting with genomic dsRNA, highlighting a novel host factor that regulates viral replication.

Development and characterization of an immortalized swine respiratory cell line for influenza A virus research

Introduction

Swine serve as an important intermediate host species for generating novel influenza A viruses (IAVs) with pandemic potential because of the host's susceptibility to IAVs of swine, human and avian origin. Primary respiratory cell lines are used in IAV research to model the host's upper respiratory tract in vitro. However, primary cell lines are limited by their passaging capacity and are time-consuming for use in industry and research pipelines. We were interested in developing and characterizing a biologically relevant immortalized swine respiratory cell line that could be used for efficient propagation and characterization of swine IAV isolates.

Methods

Lung tissue for the generation of primary swine respiratory cells were isolated from the bronchi of an 8-week-old Yorkshire/Hampshire pig, which were immortalized by transduction of the SV40 T antigen using a lentivirus vector. The transduction of the SV40 T antigen was confirmed by Real Time RT-PCR in cells passaged greater than twenty times.

Results

Immortalized swine respiratory cells expressed primarily α2,6 sialic acid receptors and were susceptible to both swine and human IAVs, with swine viruses exhibiting higher replication rates. Notably, infection with a swine H3N2 isolate prompted increased IL-6 and IL-1α protein secretion compared to a seasonal human H3N2 virus. Even after 20 passages, the immortalized cells maintained the primary respiratory cell phenotype and remained permissive to IAV infection without exogenous trypsin.

Discussion

In summary, our developed immortalized swine respiratory cell line offers an alternative in vitro substrate for studying IAV replication and transmission dynamics in pigs, overcoming the limitations of primary respiratory cells in terms of low passage survivability and cost.

Porcine Circovirus Modulates Swine Influenza Virus Replication in Pig Tracheal Epithelial Cells and Porcine Alveolar Macrophages

The pathogenesis of porcine circovirus type 2b (PCV2b) and swine influenza A virus (SwIV) during co-infection in swine respiratory cells is poorly understood. To elucidate the impact of PCV2b/SwIV co-infection, newborn porcine tracheal epithelial cells (NPTr) and immortalized porcine alveolar macrophages (iPAM 3D4/21) were co-infected with PCV2b and SwIV (H1N1 or H3N2 genotype). Viral replication, cell viability and cytokine mRNA expression were determined and compared between single-infected and co-infected cells. Finally, 3'mRNA sequencing was performed to identify the modulation of gene expression and cellular pathways in co-infected cells. It was found that PCV2b significantly decreased or improved SwIV replication in co-infected NPTr and iPAM 3D4/21 cells, respectively, compared to single-infected cells. Interestingly, PCV2b/SwIV co-infection synergistically up-regulated IFN expression in NPTr cells, whereas in iPAM 3D4/21 cells, PCV2b impaired the SwIV IFN induced response, both correlating with SwIV replication modulation. RNA-sequencing analyses revealed that the modulation of gene expression and enriched cellular pathways during PCV2b/SwIV H1N1 co-infection is regulated in a cell-type-dependent manner. This study revealed different outcomes of PCV2b/SwIV co-infection in porcine epithelial cells and macrophages and provides new insights on porcine viral co-infections pathogenesis.