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Early Immune Responses to Marek’s Disease Vaccines

Viral Immunology 2017 v.30 no.3 pp. 167-177
CD4-positive T-lymphocytes, Mardivirus, Marek disease, adaptive immunity, animal organs, antigens, cecum, chickens, disease resistance, duodenum, epithelium, gene expression, gene expression regulation, genes, immune response, immunohistochemistry, innate immunity, macrophages, peripheral nerves, tonsils, vaccination, vaccines, virulent strains, viruses
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.