Gut microbiota modulates type I interferon and antibody-mediated immune responses in chickens infected with influenza virus subtype H9N2

Abstract

Commensal gut microbes play a critical role in shaping host defences against pathogens, including influenza viruses. The current study was conducted to assess the role and mechanisms of action of commensal gut microbiota on the innate and antibody-mediated responses of layer chickens against influenza virus subtype H9N2. A total of 104 one-day-old specific pathogen free chickens were assigned to either of the four treatments, which included two levels of antibiotics treatment (ABX- and ABX+) and two levels of H9N2 virus infection (H9N2- and H9N2+). At day 17 of age, chickens in the H9N2+ group were infected via the oral-nasal route with 400 μl of 107 TCID/ml (200 μl/each route). Oropharyngeal and cloacal swabs at days 1, 3, 5, 7 and 9 post-infection (p.i.) for virus shedding, tissue samples at 12 h, 24 h and 36 h p.i. for mRNA measurement, and serum samples at days 7 and 14 p.i. for hemagglutination inhibition (HI) assay and IgG antibodies were collected. Virus shedding analysis showed that antibiotic treated (depleted)-H9N2 virus infected chickens showed a significantly higher oropharyngeal virus shedding at all time points, and cloacal shedding at days 3 and 5 p.i. compared to control treated (undepleted)-H9N2 infected chickens. Analysis of mRNA expression showed that infection of depleted chickens with H9N2 virus resulted in significantly down-regulated type I interferon responses both in the respiratory and gastrointestinal tracts compared to undepleted-H9N2 infected chickens. However, antibody-mediated immune response analysis showed a significantly higher HI antibody titre and IgG levels in the serum of chickens depleted with antibiotics and infected with H9N2 virus compared to undepleted-H9N2 infected chickens. In conclusion, findings from the current study suggest that the gut microbiota of chickens plays an important role in the initiation of innate responses against influenza virus infection, while the antibody-mediated immune response remains unaffected.

The Intestinal Microbiota Contributes to the Control of Highly Pathogenic H5N9 Influenza Virus Replication in Ducks

“…Here we provide evidence that ABX-mediated depletion of the intestinal microbiota caused an increase in H5N9 HPAIV replication in the digestive tract of ducks and was associated with a reduction of the antiviral immune response in the intestine. Similar results were observed in the digestive tract of chickens infected with a LPAIV (18, 19). Depletion of the gut microbiota in mice and chicken was associated with an increase in influenza virus replication in the respiratory tract (13, 14, 18, 19).…”

“…Similar results were observed in the digestive tract of chickens infected with a LPAIV (18, 19). Depletion of the gut microbiota in mice and chicken was associated with an increase in influenza virus replication in the respiratory tract (13, 14, 18, 19). By contrast, we did not detect a significant increase in influenza virus replication in the respiratory tract of ducks suggesting that this difference could be due to the viral strain used or host factors.…”

“…The contribution of the gut microbiota to the control of influenza virus replication has been studied in mice, as well as in chickens infected with a LPAIV (13, 14, 16–19, 23). How the gut microbiota modulates HPAIV infection, or more generally influenza virus infection in ducks has to our knowledge never been investigated.…”

“…Increased influenza virus replication and excretion in chickens (18, 19) and ducks treated with ABX raises questions about the risks associated with ABX treatments administered to farmed animals. However, the ABX treatment used to deplete the gut microbiota in our study and in the vast majority of experimental studies consists of a broad-spectrum ABX cocktail composed of six antimicrobial molecules, including molecules which are not allowed to be used in veterinary medicine as their use is restricted to human medicine in hospital settings or to research.…”

“…The gut microbiota is now recognized as a regulator of many physiological functions in the host, reaching far beyond its contribution to digestion (12). Several studies have highlighted the role of the gut microbiota in shaping the antiviral immune response against influenza virus, in mammals, in which the virus replicates in the respiratory tract (13–17), as well as following LPAIV infection in chickens, in which the virus replicates in the respiratory and digestive tract (18, 19).…”