Ontogeny of the interferon system in chickens

https://doi.org/10.1016/j.jri.2012.02.008Get rights and content

Abstract

Newborn vertebrates may be susceptible to infection because the immature status of their immune system results in an inability to make an effective immune response. Consequently, newly hatched chicks appear to be more susceptible to infections than mature chickens. In particular, poultry susceptibility to virus infection may be related to poor expression of innate immune elements involved in antiviral responses. Therefore, in this study we assessed the relative development of the interferon (IFN) system: a protective system against virus infection. We investigated the age-related expression of the elements involved in the IFN response including IFN gene expression, their associated receptors and the pattern recognition receptors (PRR) involved in the regulation of IFNs. We observed that the IFN system is somewhat inadequately expressed in embryos and develops over time, just prior to and after hatching, and therefore chicks may be more susceptible to virus than mature birds because of an immature IFN network.

Introduction

Interferons (IFNs) are an important family of proteins involved in protecting the vertebrate host from viruses. In the chicken, type I IFN includes IFN-α and IFN-β (Kaiser et al., 2005), type II IFN comprises IFN-γ (Digby and Lowenthal, 1995) and type III IFN consists of IFN-λ (Karpala et al., 2008b). The rapid mobilisation of type I and type III IFNs is critical to the outcome of viral infection (Saenz et al., 2010). Furthermore, these IFNs are regulated by the host PRR, including the RIG-like helicases and the TLR (Le Goffic et al., 2007). These protective mechanisms develop during embryogenesis and mature throughout early life and as a result, young animals may appear to be more susceptible to opportunistic infections (Hume et al., 1998). For example, susceptibility of poultry to Salmonella enterica appears to depend on age, which may indicate that immune development is a determinant in disease outcome (Abdul-Careem et al., 2007, Beal et al., 2004). Nevertheless, little is known regarding the development of the antiviral-related components of the innate immune system, such as the IFN network, which may be important for understanding age-related susceptibility to viral infection in the chicken.

The development of the chicken immune system has been investigated to some extent from early embryogenesis and throughout the post-hatch period (Abdul-Careem et al., 2007). Typical findings show that large developmental changes occur immediately post-hatch (Abdul-Careem et al., 2007, Lammers et al., 2010, Reemers et al., 2010, Schokker et al., 2009). For example, some cytokines can be detected at day 12 of embryogenesis (E12), but appear to increase rapidly around 1 day post-hatch (Abdul-Careem et al., 2007). Interestingly, whilst IFN-γ markedly increases in the spleen during the first week post-hatch (Abdul-Careem et al., 2007) the relative levels of IFN-γ increase at around two weeks post-hatch in the intestine (Lammers et al., 2010). Thus, immune competence may be organ-specific as well as age-specific.

With this in mind, immune competence and localised immune responses in the lungs may be decisive for resolving respiratory viral infections. One study that compared age-related global gene expression in the lung and trachea of the chicken found that four-week-old birds more highly upregulated innate immune genes than one-week-old birds following influenza infection (Reemers et al., 2010). Although in this case a larger infection-induced response suggested greater immune competence in the lungs of older chickens, it has been suggested that one-week-old birds have higher constitutive levels of innate immune genes that compensate for immature adaptive immunity in younger animals (Levy, 2007, Reemers et al., 2010). A reliance on innate immunity to control infection is similarly evident in mature animals, whereby early IFN activity controls infection until a delayed cellular response is able to clear the infection. The reliance on localised innate responses, such as IFN, may be highly critical whilst the adaptive immune system matures, such as in the early life of the chicken (Levy, 2007).

As the IFN network is a key to early management and control of viral infection (Cheng et al., 2010, Karpala et al., 2008b, Szretter et al., 2009), knowledge of the age that this response mechanism develops is important for developing new strategies for improved poultry health. The chicken embryo is able to be stimulated to express IFN as early as E15, which supports the functional importance of this system in the young animal (Sekellick et al., 1990). However, at present there is a paucity of information around which organs have developed this capability, and further, which components of the IFN system are regulated as a function of age. Since the lung and spleen are critical to many virus infections we investigated the IFN system in these organs in the chicken. Additionally, type I and III IFN mediate their effects by interacting with their respective IFN receptor to induce specific antiviral activities. The IFN receptors are required to promote this antiviral state, but it is not known when these receptors are present during development. Furthermore, IFN is regulated by the PRR networks including Mda5, TLR3 and TLR7 following the detection of viral RNA (Le Goffic et al., 2007); however, currently there is little information about the age that these receptor levels are present. Therefore, we measured the expression levels of the PRRs involved in virus-induced IFN as well as the type I and III IFNs and their associated receptor complexes. Knowledge of the expression levels of these systems throughout embryogenesis and the early post-hatch period may help to understand age-related susceptibility to viral infection, and may be of further interest for understanding the relative effectiveness of pre-natal and early vaccination of chicks.

Section snippets

Chickens

Specific pathogen free (SPF) white leghorn chickens (two or six weeks old) were purchased from a commercial supplier (SPAFAS, Australia) for use in this study. Chickens were housed in purpose-built isolators, were fed commercial rations and had continuous access to water. SPF eggs (SPAFAS) were incubated at 37°. All research involving animals was approved by the Australian Animal Health Laboratory (AAHL) Animal Ethics Committee.

Tissue preparation

Chickens (n = 4 per group), or chicken embryos were sacrificed at the

Type I and III IFN levels increase in the lung and spleen during embryonic development

We analysed the IFN system in the lung and spleen of the chicken across various developmental stages by qRT-PCR. In the lung the relative levels of type I and type III IFN increased across embryogenesis. The levels of IFN-α, IFN-β and IFN-λ increased 100-fold, 55-fold and 45-fold respectively at E18 relative to E10 (Fig. 1). Interestingly, the IFN-α and IFN-β expression profile showed that peak levels occurred at E18 and lower levels following this period, whereas in contrast, IFN-λ continued

Discussion

Age-related susceptibility to disease in animals may be associated with a maturing immune system. Here we show the development of important elements of the chicken antiviral immune system that may relate to the ability to protect against virus. Our focus was on type I and type III IFN systems since these mechanisms are known to be critical to virus resistance (Beilharz et al., 2007, Koerner et al., 2007). We have shown that these IFNs are expressed in the chicken at an early developmental

References (25)

  • M.E. Hume et al.

    Reduction of caecal Listeria monocytogenes in Leghorn chicks following treatment with a competitive exclusion culture (PREEMPT)

    Lett. Appl. Microbiol.

    (1998)
  • N.A. Jewell et al.

    Lambda interferon is the predominant interferon induced by influenza A virus infection in vivo

    J. Virol.

    (2010)
  • Cited by (0)

    View full text