Bursal transcriptome profiling of different inbred chicken lines reveals key differentially expressed genes at 3 days post-infection with very virulent infectious bursal disease virus

Abstract

Infectious bursal disease is a highly contagious disease in the poultry industry and causes immunosuppression in chickens. Genome-wide regulations of immune response genes of inbred chickens with different genetic backgrounds, following very virulent infectious bursal disease virus (vvIBDV) infection are poorly characterized. Therefore, this study aims to analyse the bursal tissue transcriptome of six inbred chicken lines 6, 7, 15, N, O and P following infection with vvIBDV strain UK661 using strand-specific next-generation sequencing, by highlighting important genes and pathways involved in the infected chicken during peak infection at 3 days post-infection. All infected chickens succumbed to the infection without major variations among the different lines. However, based on the viral loads and bursal lesion scoring, lines P and 6 can be considered as the most susceptible lines, while lines 15 and N were regarded as the least affected lines. Transcriptome profiling of the bursa identified 4588 genes to be differentially expressed, with 2985 upregulated and 1642 downregulated genes, in which these genes were commonly or uniquely detected in all or several infected lines. Genes that were upregulated are primarily pro-inflammatory cytokines, chemokines and IFN-related. Various genes that are associated with B-cell functions and genes related to apoptosis were downregulated, together with the genes involved in p53 signalling. In conclusion, bursal transcriptome profiles of different inbred lines showed differential expressions of pro-inflammatory cytokines and chemokines, Th1 cytokines, JAK-STAT signalling genes, MAPK signalling genes, and their related pathways following vvIBDV infection.

Transcriptomic Analysis of Inbred Chicken Lines Reveals Infectious Bursal Disease Severity Is Associated with Greater Bursal Inflammation In Vivo and More Rapid Induction of Pro-Inflammatory Responses in Primary Bursal Cells Stimulated Ex Vivo

“…Birds were weighed daily and monitored for clinical signs at least twice daily. Clinical scores were recorded according to a points-based scoring system developed at The Pirbright Institute [18] that characterized disease as mild (1-7), moderate (8)(9)(10)(11), or severe (12)(13)(14)(15)(16)(17). Briefly, birds were scored on their appearance, behavior with and without provocation and handling, and included an assessment of the combs, wattles, feathers, posture, eyes, breathing, interactions with the rest of the flock, ability to evade capture, and crop palpation [18].…”

“…So-called “resistant” White Leghorn lines 15I (herein referred to as 15), 7 2 , C, EB and O displayed no mortality, whereas mortality rates for White Leghorn lines N, 6 1 and W were 6.5%, 8.3% and 24.4%, respectively, and the mortality rates for Rhode Island Red, Light Sussex and Brown Leghorn breeds were 22.2%, 40.7%, and 79.2%, respectively [ 6 , 7 ]. To identify gene targets that could be exploited to engineer IBD resistant chickens, several groups have conducted transcriptional profiling of the BF of the lines following IBDV infection, either by microarray [ 8 , 9 ] or by RNA-sequencing (RNA-seq) [ 10 , 11 ]. Two studies [ 8 , 9 ] compared White Leghorn line 6 1 (8.3% mortality) with Brown Leghorn chickens (79.2% mortality) and their results indicated that an early, rapid, pro-inflammatory response and more extensive activation of apoptosis was evident in the more resistant line, suggesting that these responses may limit viral replication and pathology [ 8 ].…”

“…White Leghorns represent one of the leading egg-producing chicken breeds of the world and there is interest in engineering more IBD-resistant birds from this breed. In order to address this, two subsequent studies examined differences in the transcriptional responses of only the inbred lines that were of the White Leghorn breed [ 10 , 11 ]. Birds from line P, that had more severe bursal pathology than line N, demonstrated greater up-regulation of pro-inflammatory cytokines, suggesting that excessive inflammation correlated with disease severity among the White Leghorn lines, consistent with the previous observations made in LT chickens [ 11 ].…”

An <em>Ex Vivo</em> Chicken Primary Bursal-cell Culture Model to Study Infectious Bursal Disease Virus Pathogenesis

“…However, when B cells are removed from a bird, they do not survive well in ex vivo culture 2 , making it difficult to perform a thorough analysis of the interactions of IBDV with chicken B cells, or the early events following ALV or REV infection. Consequently, many host cell-virus interactions have been studied in vivo 3 4 5 6 7 8 9 10 . Although these studies are informative, they involve the use of infected birds which suffer from diseases that can be severe.…”

Edible vaccines to combat Infectious Bursal Disease of poultry

“…Poultry industry is a domineering section of agriculture sector in the world as it provides meat, income and employment. Of the poultry industry, broiler chicken is dominating, as US export was more than 41 billion pounds of chicken (about 16.5 percent of production) in 2017 [1]. In Pakistan, the poultry industry contributes around 1.4 percent to the GDP and 31 percent to total meat production [2].…”