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

Abstract

Swine influenza virus (SIV) can cause respiratory illness in swine. Swine contribute to influenza virus reassortment, as avian, human, and/or swine influenza viruses can infect swine and reassort, and new viruses can emerge. Thus, it is important to determine the host antiviral responses that affect SIV replication. In this study, we examined the innate antiviral cytokine response to SIV by swine respiratory epithelial cells, focusing on the expression of interferon (IFN) and interferon-stimulated genes (ISGs). Both primary and transformed swine nasal and tracheal respiratory epithelial cells were examined following infection with field isolates. The results show that IFN and ISG expression is maximal at 12 h postinfection (hpi) and is dependent on cell type and virus genotype. IMPORTANCE Swine are considered intermediate hosts that have facilitated influenza virus reassortment events that have given rise pandemics or genetically related viruses have become established in swine. In this study, we examine the innate antiviral response to swine influenza virus in primary and immortalized swine nasal and tracheal epithelial cells, and show virus strain- and host cell type-dependent differential expression of key interferons and interferon-stimulated genes.

Keywords: interferon-stimulated gene; interferons; swine influenza virus; swine nasal cells; swine tracheal cells.

FIG 1

Swine primary and immortalized cells permit SIV replication. Relative influenza M gene expression at 12 h (open) and 24 h (filled) bars are shown for H1N1-NC (a), H1N2-NC (c), H1N1-MN (e), and H3N2-NC (g). Viral titers (log₁₀) at 24 hpi for H1N1-NC (b), H1N2-NC (d), H1N1-MN (f), and H3N2-NC (h) are shown. Data represent mean ± standard error of the mean (SEM) of three replicates for M gene or plaque numbers at 24 hpi on MDCK cells. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 2

Replication of SIV isolates in swine cells. Viral titers at 24 hpi for H1N1-NC, H1N2-NC, H1N1-MN, and H3N2-NC on MDCK cells. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 3

Expression of IFN-λ. Panels show fold change in IFN-λ expression (log₁₀) between SNECs, SiNECs, STECs, and SiTECs infected with H1N1-NC (a), H1N2-NC (b), H1N1-MN (c), and H3N2-NC (d) relative to mock-infected cells and 18S rRNA as a housekeeping control. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 4

Expression of IFN-β. Panels show fold change in IFN-β expression (log₁₀) between SNECs, SiNECs, STECs, and SiTECs infected with H1N1-NC (a), H1N2-NC (b), H1N1-MN (c), and H3N2-NC (d) relative to mock-infected cells and 18S rRNA as a housekeeping control. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 5

Expression of RIG-I. Panels show fold change in RIG-I expression (log₁₀) between SNECs, SiNECs, STECs, and SiTECs infected with H1N1-NC (a), H1N2-NC (b), H1N1-MN (c), and H3N2-NC (d) relative to mock-infected cells and 18S rRNA as a housekeeping control. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 6

Expression of IRF7. Panels show fold change in IRF7 expression (log₁₀) between SNECs, SiNECs, STECs, and SiTECs infected with H1N1-NC (a), H1N2-NC (b), H1N1-MN (c), and H3N2-NC (d) relative to mock-infected cells and 18S rRNA as a housekeeping control. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 7

Expression of GBP1. Panels show fold change in GBP1 expression (log₁₀) between SNECs, SiNECs, STECs, and SiTECs infected with H1N1-NC (a), H1N2-NC (b), H1N1-MN (c), and H3N2-NC (d) relative to mock-infected cells and 18S rRNA as a housekeeping control. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.

FIG 8

Expression of OAS1. Panels show fold change in OAS1 expression (log₁₀) between SNECs, SiNECs, STECs, and SiTECs infected with H1N1-NC (a), H1N2-NC (b), H1N1-MN (c), and H3N2-NC (d) relative to mock-infected cells and 18S rRNA as a housekeeping control. Data represent mean ± SEM of three replicates. *, P < 0.05. Statistical methods used to determine significance are described in detail in Materials and Methods.