Characterization of four endogenous viral genes in semi-congenic lines of meat chickens

Characterization of insertion sites and development of locus-specific assays for three broiler-derived subgroup E avian leukosis virus proviruses

This report deals with the identification of novel elements belonging to a family of endogenous retroviruses, designated endogenous avian leukosis virus-type proviral elements (ALVE), that reside in the genome of the chicken and are closely related to exogenous avian leukosis viruses. The study of ALVE elements in the chicken genome serves as a model system for understanding the interplay between endogenous viruses and their vertebrate hosts in general, including humans. In this report, we characterize the insertion sites and describe locus-specific, diagnostic polymerase chain reaction-based assays for three previously discovered, but as yet not localized, ALVE elements. In addition, we assess the proviral integrity, provide the complete element sequence and examine the genomic environs of the three broiler-derived elements.

Response of white leghorn chickens of various B haplotypes to infection at hatch with subgroup J avian leukosis virus

White leghorn chickens from seven 15.B congenic lines (genetically similar except for genes linked to the major histocompatibility complex [MHC] B haplotype) and two Line 0.B semicongenic lines were infected at hatch with strain ADOL Hc-1 of subgroup J avian leukosis virus (ALV-J). At 5, 8, 16, and 36 wk of age, chickens were tested for viremia, serum-neutralizing antibody, and cloacal shedding. Chickens were also monitored for development of neoplasia. In the 15.B congenic lines (B*2, B*5, B*12, B*13, B*15, B*19, and B*21) there were no significant differences in the incidence of viremia between B haplotypes. In fact, infection at hatch in all of the 15.B congenic lines induced tolerance to ALV-J because 100% of these chickens were viremic and transient circulating serum-neutralizing antibody was detected in only a few chickens throughout the 36 wk experiment. However, at 16 wk of age more B*15 chickens had antibody and fewer B*15 chickens shed virus than did the 16-wk-old B*2, B*5, or B*13 chickens. Moreover, compared with B*15 chickens, a higher percentage of B*13 chickens consistently shed virus from 8 wk postinfection to termination at 36 wk postinfection. The B haplotype had a transient effect on viral clearance in Line 0.B semicongenics, as more B*13 than B*21 chickens remained viremic through 5 wk of age. Very few (0%-18%) of the Line 0.B semicongenic chickens shed virus. By 36 wk of age, all Line 0 B*13 and B*21 chickens produced serum-neutralizing antibodies and cleared the virus. These results show that following ALV-J infection at hatch the immune response is influenced transiently by the B haplotype and strongly by the line of chicken. Although this study was not designed to study the effect of endogenous virus on ALV-J infection, the data suggest that endogenous virus expression reduced immunity to ALV-J in Line 15I5, compared with Line 0, a line known to lack endogenous virus genes.