Enhanced Replication of Virulent Newcastle Disease Virus in Chicken Macrophages Is due to Polarized Activation of Cells by Inhibition of TLR7

Abstract

Newcastle disease (ND), caused by infections with virulent strains of Newcastle disease virus (NDV), is one of the most important infectious disease affecting wild, peridomestic, and domestic birds worldwide. Vaccines constructed from live, low-virulence (lentogenic) viruses are the most accepted prevention and control strategies for combating ND in poultry across the globe. Avian macrophages are one of the first cell lines of defense against microbial infection, responding to signals in the microenvironment. Although macrophages are considered to be one of the main target cells for NDV infection in vivo, very little is known about the ability of NDV to infect chicken macrophages, and virulence mechanisms of NDV as well as the polarized activation patterns of macrophages and correlation with viral infection and replication. In the present study, a cell culture model (chicken bone marrow macrophage cell line HD11) and three different virulence and genotypes of NDV (including class II virulent NA-1, class II lentogenic LaSota, and class I lentogenic F55) were used to solve the above underlying questions. Our data indicated that all three NDV strains had similar replication rates during the early stages of infection. Virulent NDV titers were shown to increase compared to the other lentogenic strains, and this growth was associated with a strong upregulation of both pro-inflammatory M1-like markers/cytokines and anti-inflammatory M2-like markers/cytokines in chicken macrophages. Virulent NDV was found to block toll-like receptor (TLR) 7 expression, inducing higher expression of type I interferons in chicken macrophages at the late stage of viral infection. Only virulent NDV replication can be inhibited by pretreatment with TLR7 ligand. Overall, this study demonstrated that virulent NDV activates a M1-/M2-like mixed polarized activation of chicken macrophages by inhibition of TLR7, resulting in enhanced replication compared to lentogenic viruses.

Biological and phylogenetic characterization of a novel hemagglutination-negative avian avulavirus 6 isolated from wild waterfowl in China

“…Thereafter, cells were absorbed with virus at 100 μl allantoic fluid containing the Hubei isolate for 1 hr in the presence or absence of TPCK‐trypsin (Sigma, Shanghai, China) and fresh medium was added into the well and then incubated with 72 hr post infection (hpi). Subsequent to infection, virus titre in the supernatants was measured using a micro‐hemagglutination assay (HA) method (Zhang et al., ).…”

Screening of immune-related differentially expressed genes from primary lymphatic organs of broilers fed with probiotic bacillus cereus PAS38 based on suppression subtractive hybridization

“…It has been found that the levels of IFN-β, IFN-γ, IL-1β and IL-4 in peripheral blood mononuclear cells of broilers were significantly up-regulated after TLR7 agonist Resiquimod was used [54]. It has also been found that the highly virulent NDV strain can block the expression of TLR7 in chicken macrophages and enhance replication [55]. In this study, interference of TLR7 down-regulated two kinds of interleukins, suggesting that TLR7 may be involved in the defense against viruses by promoting the expression of immune factors in broilers.…”

Nitric Oxide Production and Fc Receptor-Mediated Phagocytosis as Functional Readouts of Macrophage Activity upon Stimulation with Inactivated Poultry Vaccines In Vitro

“…For poultry vaccines, a good candidate for such assays is the chicken macrophage-like cell line HD11, which shows broad expression of PRRs, including toll-like receptors (TLRs) [ 16 ]. The HD11 cell line has already been employed to explore the immune-activating or immunomodulatory properties of TLR agonists [ 17 , 18 , 19 ], liposomes [ 20 ], host defense peptides [ 21 ], cytokines [ 22 , 23 , 24 ], bacteria [ 17 , 21 , 25 ], and replicating viruses [ 26 , 27 , 28 ], using nitric oxide production as a functional readout of macrophage activation. Macrophages produce nitric oxide using the enzyme-inducible nitric oxide synthase (iNOS), which is expressed upon stimulation of PRRs and downstream activation of transcription factor nuclear factor kappa B (NF-κB) [ 17 ].…”