Abstract
Marek’s disease virus (MDV), an alpha herpes virus, causes a lymphoproliferative state in chickens known as Marek’s disease (MD), resulting in severe monetary losses to the poultry industry. Because lymphocytes of bursa of Fabricius and spleen are prime targets of MDV replication during the early cytolytic phase of infection, the immune response in bursa and spleen should be the foundation of late immunity induced by MDV. However, the mechanism of the MDV-mediated host immune response in lymphocytes in the early stage is poorly understood. The present study is primarily aimed at identifying the crucial genes and significant pathways involved in the immune response of chickens infected with MDV CVI988 and the very virulent RB1B (vvRB1B) strains. Using the RNA sequencing approach, we analyzed the generated transcriptomes from lymphocytes isolated from chicken bursa and spleen. Our findings validated the expression of previously characterized genes; however, they also revealed the expression of novel genes during the MDV-mediated immune response. The results showed that after challenge with CVI988 or vvRB1B strains, 634 and 313 differentially expressed genes (DEGs) were identified in splenic lymphocytes, respectively. However, 58 and 47 DEGs were observed in bursal lymphocytes infected with CVI988 and vvRB1B strains, respectively. Following MDV CVI988 or vvRB1B challenge, the bursal lymphocytes displayed changes in IL-6 and IL-4 gene expression. Surprisingly, splenic lymphocytes exhibited an overwhelming alteration in the expression of cytokines and cytokine receptors involved in immune response signaling. On the other hand, there was no distinct trend between infection with CVI988 and vvRB1B and the expression of cytokines and chemokines, such as IL-10, IFN-γ, STAT1, IRF1, CCL19, and CCL26. However, the expression profiles of IL-1β, IL-6, IL8L1, CCL4 (GGCL1), and CCL5 were significantly upregulated in splenic lymphocytes from chickens infected with CVI988 compared with those of chickens infected with vvRB1B. Because these cytokines and chemokines are considered to be associated with B cell activation and antigenic signal transduction to T cells, they may indicate differences of immune responses initiated by vaccinal and virulent strains during the early phase of infection. Collectively, our study provides valuable data on the transcriptional landscape using high-throughput sequencing to understand the different mechanism between vaccine-mediated protection and pathogenesis of virulent MDV in vivo.
Highlights
Marek’s disease (MD) is a lymphoproliferative disease that is devastating for the poultry industry as it causes huge monetary losses (1–2 billion US dollars) annually [1]
The RT-quantitative PCR (qPCR) based on the Meq gene was employed for calculation of Marek’s disease virus (MDV) genome copy numbers in the DNA extracted from lymphocytes from infected chickens
Our results signified that the genome copy numbers of both MDV strains (CVI988 and very virulent RB1B (vvRB1B)) in splenic lymphocytes were higher than in bursal in agreement with the previously reported literature [17]
Summary
Marek’s disease (MD) is a lymphoproliferative disease that is devastating for the poultry industry as it causes huge monetary losses (1–2 billion US dollars) annually [1]. The etiological agent, Marek’s disease virus (MDV), is an alpha herpes virus that belongs to the family Herpesviridae, has tropism for immune cells (B and T cells) in vivo, and is widely known to cause oncogenic immunosuppression and lymphoma in chickens [1,2]. The MDV infection is initiated by inhalation of airborne cell-free virions present in contaminated dust and dander, which are continuously shed from the epithelium of feather follicles of the infected host. The MDV life cycle in birds comprises four phases. The early cytolytic phase (2–7 days post-infection (dpi)) is designated as the semi-productive MDV mediated lytic infection in B cells [6,7]. The second phase is termed the latent phase, and develops 7–10 dpi in T cells, which become infected and activated
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