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Figure 3 | Veterinary Research

Figure 3

From: Marek’s disease in chickens: a review with focus on immunology

Figure 3

Model of MDV neoplastic transformed CD4+ T cells and subsequent disseminated Systemic Infection in susceptible birds. 4 Fully latent MDV-Transformed CD4+ T-cells proliferate in all sites where immune systems cells are involved in primary and secondary line of defence. Early latently activated CD4+ T cells undergo neoplastic transformation due to transcriptional and transrepressional activity of viral oncogenic proteins such as Meq. Pathogenesis arise in cases where vaccination failure is suspected (suboptimal dosage/titre, damage to vaccine or confirmed immunological vaccine failure), vaccination is not performed (backyard birds). b Fully latent neoplastic MDV-Transformed CD4+ T cells infiltrate and establish a reservoir of MDV genome in peripheral nerve fibres interspace. These cells have a CD4+ CD25+ Treg phenotype although additional cell surface markers have yet to be determined. Expression of viral neurovirulence factor, phosphoprotein 14 (pp14), promotes neuropathy and cell survival. Neuropathy (Polyneuritis) is presented as transient or acute paralysis of legs, wings, neck, with vision impairment and weight loss depending on MDV-1 virulence factor. Birds infected with serotype-1 eventually succumb to death from paralysis. c Reactivation from latency enables a second phase of replication whereby viral oncogenic protein Meq acts on T cell signaling pathways causing uncontrolled cellular proliferation leading to disseminated lymphoma formation in visceral organs, peripheral and central nervous system, musculoskeletal systems, skin and eyes. Severe lymphoma eventually causes death in birds. Highly pathogenic viruses (serotype-1, vv+ MDV) kill birds before they reach the lymphoproliferative phase of the disease.

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