Naturally occurring mutations within 39 amino acids in the envelope glycoprotein of maedi-visna virus alter the neutralization phenotype

Infectious molecular clones have been isolated from two maedi-visna virus ( MW) strains, one of which (KV1772kv72/67) is an antigenic escape mutant of the other (LV1-1KS1), To map the type-specific neutralization epitope, we c onstructed viruses containing chimeric envelope genes by using KV1772kv72/6 7 as a backbone and replacing various parts of the envelope gene with equiv alent sequences from LV1-1KS1. The neutralization phenotype was found to ma p to a region in the envelope gene containing two deletions and four amino acid changes within 39 amino acids (positions 559 to 597 of Env). Serum obt ained from a lamb infected with a chimeric virus, VR1, containing only the 39 amino acids from LVI-1KS1 in the KV1772kv72/67 backbone neutralized LV1- 1KS1 but not KV1772kv72/67, The region in the envelope gene that we had thu s shown to be involved in escape from neutralization was cloned into pGEX-3 X expression vectors, and the resulting fusion peptides from both molecular clones were tested in immunoblots for reactivity with the KV1772kv72/67 an d VR1 type-specific antisera. The type-specific KV1772kv72/67 antiserum rea cted only with the fusion peptide from KV1772kv72/67 and not with that from LV1-1KS1, and the type-specific VR1 antiserum reacted only with the fusion peptide from LV1-1KS1 and not with that from KV1772kv72/67. Pepscan analys is showed that the region contained two linear epitopes, one of which was s pecific to each of the molecularly cloned viruses. This linear epitope was not bound by all type-specific neutralizing antisera, however, which indica tes that it is not by itself the neutralization epitope but may be a part o f it. These findings show that mutations within amino acids 559 to 597 in t he envelope gene of MVV virus result in escape from neutralization. Further more, the region contains one or more parts of a discontinuous neutralizati on epitope.