Innate Immune Training in Chickens for Improved Defense against Pathogens: A Review

Abstract

The avian immune system plays a vital role in poultry production to obtain good productibility and products that are safe and of high quality. Historically, adaptive immunity has been the main target of vaccination. However, over the past decade, innate immunity has been reported to be enhanced in different animals through vaccination and feed additives. This enhancement is due to innate immune memory termed "trained immunity," in which epigenetic and metabolic reprogramming play significant roles. Although reports on trained immunity in poultry are limited, several studies have suggested that vaccinations and feed additives affect the innate immunity. This review discusses the possible effects of vaccination and β-glucan on innate immunity for potential incorporation in advanced strategies to enhance the defense function in poultry while considering the information on trained immunity in mammals.

Keywords: innate immunity; reprograming; trained immunity; vaccines; β-glucan.

Fig. 1.

Toll-like receptors (TLRs), their corresponding ligands, and signal pathways to induce innate immune factor expression. Interaction of TLRs with ligands sends signals to activate the transcription factor, NF-κB, which induces innate immune molecules such as proinflammatory cytokines, cytokines, chemokines, and antimicrobial peptides. TLR2, 4, 5, and 15 are expressed on the surface of the cell membrane (shown in brown), whereas TLR3, 7, and 21 are in endosome in the cytoplasm (shown in tan).

Fig. 2.

Effects of multiple routine vaccinations on histone modification in the ovaries of chicks. (a-d) Fold change in histone modifications between vaccinated and unvaccinated chicks are shown: (a) di-methyl histone H3 (Lys9), H3K9me2; (b) di-methyl and tri-methyl histone H3 (Lys4), H3K4me2/3; (c) acetyl histone H3 (Lys9), H3K9ac; and (d) acetyl histone H3 (Lys27), H3K27ac. Chicks in the vaccine group (■) received the infectious bronchitis vaccine and Marek’s disease vaccine on day 1, mixed vaccines of Newcastle disease and infectious bronchitis on day 7, and infectious bursal disease vaccines on day 14. Control chicks (□) were administered water or dilution buffer in lieu of vaccines. Samples were collected on day 21, and the densities were examined using western blot analysis. Values represent the mean ± SEM of the densities relative to histone H3 (n = 8). Asterisks indicate significant differences between the control and vaccine groups (*P < 0.05, **P < 0.01). Data from Kang et al.[40] reproduced with permission of the publisher.

Fig. 3.

Effects of Marek’s disease (MD) and avian infectious bronchitis/Newcastle disease (IB/ND) vaccinations on the expression of toll-like receptors (TLRs) 7 and 21 in the chick kidneys. Day-old chicks were vaccinated with IB/ND or MD vaccines, and TLR gene expression was examined three days post-vaccination using real-time PCR. Chicks in the control group (Con) received no vaccine. Solid bars represent the median values within each group. Asterisks indicate significant differences between the two groups (*P < 0.05, **P < 0.01). Data from Shimizu et al.[41] reproduced with permission from the publisher.

Fig. 4.

Effects of Newcastle disease and infectious bronchitis (ND/IB) vaccination on the expression of toll-like receptors (TLRs) in the chick proventriculus. Day-old chicks were administered phosphate-buffered saline (control; C) or the ND/IB vaccine (V), and proventricular tissues were collected on the 11^th day post-hatching. Dots indicate the values for each individual. Bars represent mean ± SEM (n = 10). Asterisks indicate significant differences between the control and vaccinated groups (**P < 0.01, n = 10). Data from Yoshimura et al.[17] reproduced with permission from the publisher.