TLR Ligands Induce Antiviral Responses in Chicken Macrophages

Abstract

Chicken macrophages express several receptors for recognition of pathogens, including Toll-like receptors (TLRs). TLRs bind to pathogen-associated molecular patterns (PAMPs) derived from bacterial or viral pathogens leading to the activation of macrophages. Macrophages play a critical role in immunity against viruses, including influenza viruses. The present study was designed to test the hypothesis that treatment of chicken macrophages with TLR ligands reduces avian influenza replication. Furthermore, we sought to study the expression of some of the key mediators involved in the TLR-mediated antiviral responses of macrophages. Chicken macrophages were treated with the TLR2, 3, 4, 7 and 21 ligands, Pam3CSK4, poly(I:C), LPS, R848 and CpG ODN, respectively, at different doses and time points pre- and post-H4N6 avian influenza virus (AIV) infection. The results revealed that pre-treatment of macrophages with Pam3CSK4, LPS and CpG ODN reduced the replication of AIV in chicken macrophages. In addition, the relative expression of genes involved in inflammatory and antiviral responses were quantified at 3, 8 and 18 hours post-treatment with the TLR2, 4 and 21 ligands. Pam3CSK4, LPS and CpG ODN increased the expression of interleukin (IL)-1β, interferon (IFN)-γ, IFN-β and interferon regulatory factor (IFR) 7. The expression of these genes correlated with the reduction of viral replication in macrophages. These results shed light on the process of immunity to AIV in chickens.

Reduction of avian influenza virus shedding by administration of Toll-like receptor ligands to chickens

“…CpG with different motifs have distinct immunomodulatory effects [10,16,25]. In chickens, most studies have focused on class B CpG, such as 2007 and 1826 [3].…”

“…TLR ligands can be employed as stand-alone antibacterial or antiviral agents. For example, TLR2, 4 and 21 ligands significantly reduce replication of AIV in chicken macrophages [16]. TLR2 and 9 ligands protect mice against lethal influenza virus infection [11], and TLR2, 3, 4, 21 ligands protect against bacterial and viral infections [3].…”

“…These procedures were identical to those described previously [16]. Specific sequences of primers used for real-time PCR are listed in Table 2 [21][22][23][24].…”

Characterization of host responses induced by Toll-like receptor ligands in chicken cecal tonsil cells

“…For example in chickens, the direct interaction of TLR4 and TLR2 with microbial LPS and lipoprotein, respectively, triggers expression of pro-inflammatory cytokines by heterophils (Kogut et al, 2005;Malek et al, 2004), macrophages (St. Paul et al, 2013a;Barjesteh et al, 2014), splenocytes (St. Paul et al, 2011) and cells of the bursa of Fabricius (St. Paul et al, 2012b).…”

“…Chickens, however, do not express TLR9, but TLR21 binds DNA with similar affinity and specificity (Brownlie et al, 2009). Previous results have shown that class B CpG oligodeoxynucleotides (ODN) promote the up-regulation of interferon (IFN)-␥ and IL-10 in the bursa of Fabricius (St. Paul et al, 2012b), IFN-␥, IFN-␤, IL-1␤, and interferon regulatory factor (IFR) 7 in chicken macrophages (Barjesteh et al, 2014), IFN-␥, major histocompatibility complex (MHC)-II, and IL-10 in chicken splenocytes (St. Paul et al, 2011), IL-1␤, IL-6 and CxCLi2 in chicken thrombocytes (St. Paul et al, 2012a) and type I IFNs in chicken erythrocytes (St. Paul et al, 2013c).…”