Marek’s disease (MD) is an infectious malignant T-cell lymphoma proliferative disease caused by Marek’s disease virus (MDV). In recent years, the emergence of very virulent (vv) and/or very virulent plus (vv +) strains of MDV in the field has been suggested as one of the causes of vaccination failure. The pathogenicity of the MDV strain GX18NNM4, isolated from a clinical outbreak in a broiler breeder flock that was vaccinated with CVI988/Rispens, was investigated. In the vaccination-challenge test, GX18NNM4 was able to break through the protections provided by the vaccines CVI988 and 814. It also significantly reduced body weight gain and caused marked gross lesions and a large area of infiltration of neoplastic lymphocyte cells in the heart, liver, pancreas, etc. of the infected birds. In addition, the expressions of programmed death 1 (PD-1) and its ligand, programmed death ligand 1 (PD-L1), in the spleens and cecal tonsils (CTs) of the unvaccinated challenged birds were significantly increased compared to those in the vaccinated challenged birds, indicating that the PD-1/PD-L1 pathway is related to immune evasion mechanisms. The results showed that the GX18NNM4 strain could cause severe immunosuppression and significantly decrease the protections provided by the current commercial vaccines, thus showing GX18NNM4 to be a vv + MDV strain.

中文翻译：

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vv + MDV的出现可能会突破当前疫苗提供的保护。

马立克氏病（MD）是由马立克氏病病毒（MDV）引起的传染性恶性T细胞淋巴瘤增生性疾病。近年来，已经提出在田间出现强毒（vv）和/或强毒加（vv +）的MDV菌株是疫苗接种失败的原因之一。研究了从接种了CVI988 / Rispens的肉鸡种鸡群的临床暴发中分离出的MDV株GX18NNM4的致病性。在疫苗挑战试验中，GX18NNM4能够突破疫苗CVI988和814提供的保护作用。它还显着降低了体重增加，并引起明显的总体损害，并在心脏，肝脏中形成了大面积的肿瘤性淋巴细胞浸润，胰腺等被感染的鸟类。此外，与接种疫苗的挑战禽鸟相比，未接种疫苗的挑战禽鸟的脾脏和盲肠扁桃体（CT）中程序性死亡1（PD-1）及其配体程序性死亡配体1（PD-L1）的表达显着增加，表明PD-1 / PD-L1途径与免疫逃逸机制有关。结果表明，GX18NNM4菌株可引起严重的免疫抑制，并显着降低当前商业疫苗提供的保护作用，从而表明GX18NNM4为vv + MDV菌株。