Hypervariability in the envelope genes of subgroup J avian leukosis viruses obtained from different farms in the United States

Avian leukosis virus, subgroup J (ALV-J), has a wide host range, preferenti ally infecting meat-type birds, and produces a high incidence of myelocytom atosis and nephromas. Using the published sequences from HPRS-103 (ALV-J is olated in 1989 in Great Britain), we designed a set of PCR primers that amp lified proviral DNA from nine U.S. field samples. The primers were specific for ALV-J, not amplifying DNA from uninfected cells or cells infected with ALV subgroups A-E. These primers expanded a 2.4-kb fragment that encompass es gp85, gp37, the E element, and mast of the 3' LTR. We also developed a s et of PCR primers that amplified a 2.1-kb fragment from ALV-J-infected cell s and a 1.6-kb fragment from uninfected ev- chicken embryo fibroblasts (Lin e 0). Upon cloning and DNA sequencing, we determined that the 2.1- and 1.6- kb fragments contained ALV-J gp85- and gp37-like sequences. Comparison of t he amino acid sequences demonstrated that the Line 0 sequences were 97.5% i dentical with the gp85 and gp37 of HPRS-103 and somewhat less identical wit h the other nine U.S, isolates. This suggests that the envelope genes of AL V-J may have arisen as a result of a recombination event between exogenous ALV and Line 0-like sequences in the chicken. Phylogenetic analysis also sh owed that the U.S, field isolates were closely related to one another and m ore distantly related to the European HPRS-103. The pattern of mutations in the U.S, field isolates suggests that the U.S. strains are slowly drifting away from their progenitor Line 0-like sequences. The development of effec tive vaccines and diagnostic tests is likely to become more problematic as the Viruses continue to mutate. (C) 2000 Academic Press.