Effects of Toll-like Receptor Ligands on the Expression of Proinflammatory Cytokines and Avian β-defensins in Cultured Chick Intestine

Treatment with Toll-like Receptor (TLR) Ligands 3 and 21 Prevents Fecal Contact Transmission of Low Pathogenic H9N2 Avian Influenza Virus (AIV) in Chickens

Transmission of H9N2 avian influenza virus (AIV) can occur in poultry by direct or indirect contact with infected individuals, aerosols, large droplets and fomites. The current study investigated the potential of H9N2 AIV transmission in chickens via a fecal route. Transmission was monitored by exposing naïve chickens to fecal material from H9N2 AIV-infected chickens (model A) and experimentally spiked feces (model B). The control chickens received H9N2 AIV. Results revealed that H9N2 AIV could persist in feces for up to 60-84 h post-exposure (PE). The H9N2 AIV titers in feces were higher at a basic to neutral pH. A higher virus shedding was observed in the exposed chickens of model B compared to model A. We further addressed the efficacy of Toll-like receptor (TLR) ligands to limit transmission in the fecal model. Administration of CpG ODN 2007 or poly(I:C) alone or in combination led to an overall decrease in the virus shedding, with enhanced expression of type I and II interferons (IFNs) and interferon-stimulating genes (ISGs) in different segments of the small intestine. Overall, the study highlighted that the H9N2 AIV can survive in feces and transmit to healthy naïve chickens. Moreover, TLR ligands could be applied to transmission studies to enhance antiviral immunity and reduce H9N2 AIV shedding.

Effects of Newcastle Disease/Infectious Bronchitis Vaccine and Feeding Yeast Products on the Innate Immune System in the Proventriculus and Ileum of Broiler Chicks

The aim of this study was to determine whether Newcastle disease/infectious bronchitis (ND/IB) vaccination and yeast product diet supplementation modulate the expression of innate immune molecules in the proventriculus and ileum of broiler chicks. One-day-old male broiler chicks were divided into four groups (V-Y- (control), V-Y+, V+Y-, and V+Y+ groups, where V and Y represent vaccination and yeast product supplementation, respectively). Chicks in the V+Y- and V+Y+ groups were immunized with the live ND/IB vaccine, whereas chicks in the V-Y- and V-Y+ groups were not. Chicks in the V-Y+ and V+Y+ groups received feed containing yeast products from day 4, whereas chicks in the V-Y- and V+Y- groups did not. The proventriculus and ileum were collected on day 7 to analyze the expression of seven Toll-like receptors (TLRs) and Dectin-1. In the proventriculus, compared with those of the V-Y- control group, the TLR7 and TLR21 expression levels were higher in the V+Y- group; however, there were no differences in the expression levels of any TLR or Dectin-1 in the ileum. There were also no differences in the expression of avian β-defensins and cathelicidin-1 in the proventriculus and ileum between the control and treatment groups. The expression of granzyme in cytotoxic cells and interleukin (IL)-1B was upregulated by ND/IB vaccination in the proventriculus. Supplementation with yeast products upregulated only granzyme expression in the ileum and downregulated IL-6 expression in the proventriculus in chicks immunized with the ND/IB vaccine. Thus, we concluded that ND/IB vaccination is effective at enhancing the innate immune system in the proventriculus of chicks, at least until day 7 post-hatching, whereas the effects of diet supplementation with yeast products may be limited, at least under the present study conditions.

Modulation of the innate immune system by lipopolysaccharide in the proventriculus of chicks inoculated with or without Newcastle disease and infectious bronchitis vaccine

This study aimed to determine whether the innate immune system in the proventriculus of broiler chicks responds to lipopolysaccharide (LPS) and whether this response is affected by Newcastle disease and infectious bronchitis (ND/IB) vaccination. Chicks were divided into 4 groups: nonvaccinated and injected with PBS or LPS (V-L- and V-L+), and vaccinated and injected with PBS or LPS (V+L- and V+L+). Vaccination was performed on d 1, and LPS was intraperitoneally injected on d 11 of age. The gene expression and protein levels of immune molecules, including toll-like receptors (TLRs), antimicrobial peptides, interleukin-1β (IL-1B), and immunoglobulin A (IgA) in the proventriculus and serum were analyzed. The results showed that the expression levels of TLR21 were higher in vaccinated (V+L-) group than in nonvaccinated (V-L-) group. Gene expression levels of avian β-defensin (AvBDs) and cathelicidin1 (Cath1) were not different among the 4 groups. However, the results of LC/MS analysis showed that the levels of AvBD2, 6, and 7 significantly increased after the LPS challenge in nonvaccinated and vaccinated chicks; the levels were higher in V-L+ and V+L+ than in V-L- and V+L-, respectively. Immunohistochemistry analysis revealed the localization of AvBD1 protein in the epithelial cells of the surface glands and AvBD2 and CATH1 in the heterophil-like cells in the lamina propria of surface glands. Although IL-1B gene expression and protein concentration in the proventriculus tissues were not different among the 4 groups, serum IL-1B levels were upregulated by LPS in both the nonvaccinated and vaccinated groups (V-L- vs. V-L+, V+L- vs. V+L+). Moreover, IgA levels in the proventriculus and serum were not affected by vaccination or LPS challenge. Taken together, we conclude that LPS derived from gram-negative bacteria upregulates the innate immune system, including antimicrobial peptide synthesis in the proventriculus. ND/IB vaccination may not significantly affect antimicrobial peptide synthesis in response to LPS; however, TLR21 expression is upregulated by that vaccination. The antimicrobial peptides synthesized in the proventriculus probably prevent pathogenic microbes from entering the intestine.

Effect of antibiotic treatment on microbial composition and expression of antimicrobial peptides and cytokines in the chick cecum

The aim of this study was to confirm whether the expression of innate immune molecules in the chick cecum is altered in association with changes in the composition of the intestinal microbiome that are regulated by treatment with antibiotics. Broiler chicks were administered with antibiotics (penicillin and streptomycin) daily, and the composition of the microbiota, expression of innate immune molecules, and localization of antimicrobial peptides in the chick cecum were examined at day 7 and day 14 using real-time PCR and immunohistochemistry. The oral administration of antibiotics caused an increase in the relative frequency of the Enterobacteriaceae family and a decrease in some gram-negative (Barnesiellaceae) and gram-positive bacterial (Clostridiaceae and Erysipelotrichaceae) families. The gene expression levels of immune molecules, including 4 Toll-like receptors (TLR) (TLR 2, 4, 5, and 21), inflammation-related cytokines (IL-1β, TGFβ3, TGFβ4, and IL-8), and antimicrobial peptides (avian β-defensins and cathelicidins) showed a tendency to decrease with antibiotic treatment at day 7. However, expression levels of TLR21 and some cytokines (IL-1β, TGFβ3, and IL-8) were higher in the cecum or cecal tonsils of the antibiotic-treated group than in those of the control at day 14. The immunoreactive avian β-defensin 2 and cathelicidin 1 proteins were localized in the leukocyte-like cells in the lamina propria, and they were aggregated in the form of small islands. We conclude that the expression of innate immune molecules, including TLR, inflammation-related cytokines, and antimicrobial peptides, in the cecum are altered in association with changes in the density or composition of the luminal microbiota during the early phase of life in chicks.

Effects of Probiotics Lactobacillus reuteri and Clostridium butyricum on the Expression of Toll-like Receptors, Pro- and Anti-inflammatory Cytokines, and Antimicrobial Peptides in Broiler Chick Intestine

The aim of this study was to determine the effects of live probiotics Lactobacillus reuteri (LR) and Clostridium butyricum (CB) on the expression of genes of innate immune system in broiler chick ileum and cecum. Chicks were administered 500 µl water with or without LR or CB, daily from day 1 to 6 after hatching. The ileum and cecum were collected on day 7 for analysis of gene expression of Toll-like receptors (TLRs), pro- and anti-inflammatory cytokines, and antimicrobial peptides (AMPs) using real-time PCR. The expression of TLR2-1 was upregulated by CB in the ileum and that of TLR5 was upregulated by both LR and CB. Expression of IL-1β and TGFβ2 in the ileum and of TGFβ3 and TGFβ4 in the cecum was upregulated by both LR and CB. The gene expressions of avian β-defensin (AvBD) 1 and cathelicidin (CATH) 3 were upregulated by CB and that of AvBD4 was upregulated by LR in the cecum. However, the expression of CATH2 in the ileum was downregulated by LR. These results suggest that probiotic LR and CB treatments affect a part of the innate defense system in the ileum and cecum by modulating the expression of innate immune molecules including TLRs, pro- and anti-inflammatory cytokines, and AMPs.