Duck innate immune responses to high and low pathogenicity H5 avian influenza viruses

Abstract

Ducks are the reservoir host of influenza, and are permissive for replication of most strains, yet can elicit robust innate immune responses to highly pathogenic strains. Tissue tropism and viral amino acid differences affect virulence, but we have limited knowledge about how viral differences influence the host innate immune response. Here we compare the innate immune response in Pekin ducks to a recombinant highly-pathogenic avian influenza (HPAI) H5N1 virus and a naturally arising attenuated variant of this strain that differs at one amino acid in polymerase A (T515A), as well as ducks infected with two different H5 strains of low pathogenic avian influenza (LPAI). Using qPCR we examined the relative abundance of transcripts for RIG-I and interferon-beta (IFNβ), and downstream interferon stimulated genes (ISGs). The polymerase PA (T515A) mutation did not significantly affect replication in vivo but greatly attenuated host interferon responses. ISG induction was robust for both H5N1 strains, but was three times lower for the PA mutant strain. Low pathogenic viruses elicited detectable induction of RIG-I, IFNβ and ISGs in lung and intestine tissues that correlated with the recovery of viruses from tracheal or cloacal swabs. Several genes in the MAVS signaling pathway were also upregulated by H5N1, which contributed to further amplification of the signal. We also examined hematoxylin-eosin stained tissue sections and observe evidence of lung pathology and splenocyte depletion with both H5N1 viruses at 3 dpi, and recovery by 6 dpi. However, for both H5N1 strains we observed inflammation around neurons in brain, with increased cytokine expression in some individuals. Our findings reveal HPAI H5N1 viruses induced stronger innate immune responses to the infection, while LPAI viruses elicit a milder response.

Pattern Recognition Receptor Signaling and Innate Responses to Influenza A Viruses in the Mallard Duck, Compared to Humans and Chickens

“…PKR is upregulated in ducks infected with both HPAI and (to a lesser extent) LPAI virus (Fleming-Canepa et al, 2019) but to date we are unaware of any studies functionally characterizing duck PKR during influenza infection. We previously thought that ducks appeared to be missing the second dsRNA-binding domain (Fleming-Canepa et al, 2019), also confirmed by another group . However, through transcriptomic assembly done in our lab we have since found a transcript of the full-length PKR, which contains the second dsRNA-binding domain previously thought to be missing.…”

“…RIG-I is upregulated quickly during influenza infection, with a peak at 24 h and expression returning to normal levels in lung, intestine, and spleen when Pekin ducks are infected with both HPAI and LPAI IAV strains (Fleming-Canepa et al, 2019). In these studies, RIG-I is upregulated much more during HPAI infection than LPAI infection.…”

“…Chicken MDA5 is strongly upregulated in lung, spleen and brain in H5N1 infected birds (Karpala et al, 2011). Duck MDA5 is upregulated in response to IAV infection at 1 DPI in the lung, spleen, and brain, and returns to normal levels at 3 DPI (Wei et al, 2014;Fleming-Canepa et al, 2019). MDA5 was also slightly upregulated in lungs of Pekin ducks infected with LPAI, but not significantly upregulated in intestines of the same cohort of ducks (Fleming-Canepa et al, 2019).…”

“…The human protein atlas shows that human MAVS is expressed in almost all tissues, but curiously has the lowest expression in innate immune cells such as dendritic cells, monocytes, T-cells and B-cells (Uhlen et al, 2015). Pekin duck MAVS is upregulated 1 DPI in both HPAI and LPAI infection in lungs, however no MAVS upregulation was seen in ileum of LPAI infected ducks (Fleming-Canepa et al, 2019).…”

“…In Newcastle disease (NDV) infected ducks, viperin was found to be highly upregulated after 24 h in the blood and peaked in expression in the lung and brain at 72 HPI (Zhong et al, 2015). Viperin is one of the most highly upregulated genes in duck lungs in response to H5N1 HPAI infection (Fleming-Canepa et al, 2019), however, the levels of viperin expression in chickens infected with the same strain of H5N1 was not mentioned (Smith et al, 2015). Ducks also significantly upregulated viperin in response to LPAI in the lung, but curiously not in the ileum (Fleming-Canepa et al, 2019).…”