Early immune responses to Marek’s disease vaccines

Authors: Heidari, Mohammad; DAN, WANG - Shandong Agricultural University; SHUHONG, SUN - Shandong Agricultural University

Submitted to: Viral Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2016
Publication Date: 4/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5700714
Citation: Heidari, M., Dan, W., Shuhong, S. 2017. Early immune responses to Marek’s disease vaccines. Viral Immunology. doi:10.1089/vim.2016.0126.

Interpretive Summary: Marek’s disease virus, the etiological agent of Marek’s disease (MD), is a herpes virus that causes the suppression of immune system and evasion of immune responses in the infected chickens. Despite the success and availability of several vaccines that have greatly reduced the losses from MD, the molecular mechanism of vaccine-induced immunity is unknown. MD remains as a major economical threat to the poultry industry and consequently, elucidation of immune mechanisms of vaccine-induced protection is of critical importance. In this study, we investigated the role of innate immune responses to Rispens, a commercial MD vaccine, in two MD-susceptible and resistant lines. Differential expression of Natural Killer (NK) cell-specific genes in the cecal tonsils and duodenum of the vaccinated birds revealed activation of NK cells and a robust innate immune response to vaccination. Absence of an increase in the population of T cells in the tested tissues of the vaccinated birds at 3 and 5 days post vaccination (dpv) was suggestive of lack of an involvement of adaptive immune responses to the early stages of vaccination. Additionally, vigorous replication of the vaccine strain virus in the cecal tonsils and duodenum of the vaccinated susceptible line was detected by a Rispens-specific monoclonal antibody at 5 dpi. This study provides further insight into the role of the innate immune system in vaccine-induced protection and possible development of new recombinant vaccines with enhanced innate immune system activation properties

Technical Abstract: Marek’s disease virus (MDV), a highly cell-associated lymphotropic 'alpha-herpesvirus, is the causative agent of Marek’s disease (MD) in domestic chickens. MDV replicates in chicken lymphocytes and establishes a latent infection within CD4+ T cells. The latently infected CD4+ T cells carry the virus to visceral organs, peripheral nerves, and feather follicle epithelium (FFE). Although MD vaccines have been in use for several decades, the exact mechanism of vaccine-induced protection is unclear. It is believed that the innate immune system plays a role in vaccine-induced immunity against pathogenic strains of MDV. To shed light on the possible function of the innate immunity on vaccine-mediated protection, we investigated the effect of vaccination, Rispens/CVI988, on the activation of cellular components of the innate immune system by analyzing the expression pattern of a select immune related genes in the cecal tonsils (CT) and duodenum of two MD-susceptible and resistant chicken lines at 3, 5, and 10 days post vaccination (dpv). The differential expression patterns of the tested genes within the CT and duodenum of the vaccinated birds revealed the activation of the innate immune system in both the susceptible and resistant lines. Stronger innate immune response was induced within the CT of the vaccinated birds of the susceptible line at 5 dpv. Up regulation of some the tested genes at 10 dpv was likely due to the activation and response of the adaptive immune system to vaccination. Immunohistochemical analysis showed no increase in the number of CD3+ T cells in the duodenum or cecal tonsils of the vaccinated birds of either line at 5 dpv. There was, however, an increase in the macrophage populations within the duodenum of the vaccinated birds of both the susceptible and resistant lines at 5 dpv. The vaccine strain antigen was detected in the duodenum and CT of the susceptible line but not the resistant line at 5 dpv