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Endogenous avian leukosis virus in combination with serotype 2 Marek’s disease virus boosted the incidence of LL-like bursal lymphomas in susceptible chickens

Mays Jody K., Black-Pyrkosz Alexis, Mansour Tamer, Schutte Brian C., Chang Shuang, Dong Kunzhe, Hunt Henry D., Fadly Aly M., Zhang Lei, Zhang Huanmin
Journal of virology 2019 v.93 no.23 pp. 00861
Avian leukosis virus, Marek disease, Mardivirus, broiler breeders, chicks, disease incidence, farms, flocks, gene expression regulation, genes, immune system, lymphoma, sequence analysis, serotypes, signal transduction, tissues, vaccination, vaccines
Sporadic avian leukosis virus (ALV)-like bursal lymphoma, also known as spontaneous lymphoid leukosis (LL)-like tumors, were identified in commercial broiler breeder flocks in the absence of exogenous ALV infection. Two individual ALV subgroup E (ALV-E) field strains, designated AF227 and AF229, were isolated from two different breeder farms. The role of these ALV-E field isolates in development of spontaneous LL-like tumors and the potential joint impact in conjunction of a Marek’s disease (MD) vaccine (SB-1) on enhancement of the spontaneous LL-like tumor formation were further characterized in chickens of an experimental line and breeders of commercial broiler lines. The experimental line, 0.TVB*S1, commonly known as Rapid Feathering Susceptible (RFS) line, of chickens lack all endogenous ALV and are fully susceptible to all subgroups of ALV including ALV-E. Spontaneous LL-like tumors occurred following infection with the AF227, AF229, and a reference ALV-E strain, RAV60, in the RFS chickens. Vaccination with serotype 2 Marek’s disease viruses, SB-1, in addition to AF227 or AF229 inoculation, significantly enhanced the spontaneous LL-like tumor incidence in the RFS chickens. The spontaneous LL-like tumor incidence jumped from 14% by AF227 only to 42-43% by AF227 in combination with SB-1 in the RFS chickens under controlled conditions. RNA-Seq analysis of the LL-like lymphomas and non-malignant bursa tissues of the RFS line of birds identified hundreds of differentially expressed genes, which are reportedly involved in key biological processes and pathways including signaling and signal transduction pathways. The data from this study suggested that both ALV-E and MDV-2 play an important role in enhancement of the spontaneous LL-like tumors in susceptible chickens. The underlying mechanism may be complex, which is potentially involved with many chicken genes and pathways including signaling, signal transduction pathways and immune system processes, in addition to reported viral genes.