Neutralizing antibody responses and evolution of antigenic variants in monozygotic twin lambs infected with phenotypically distinct ovine lentiviruses

Ovine lentivirus (OvLV) isolates 85/34 (OvlV 34) and 84/28 (OvLV 28) were initially characterized as phenotypically distinct "rapid/high" and "slow/low" strains based on replication kinetics, syncytiogenesis, and cell lysis in vitro. In the present study, sera from OvLV-34- or OvLV-28-infected monozygotic twin lambs defined these virus strains as distinct neutralization serotypes. We also show that immune recognition of at least one OvlV neutralization epitope is influenced by genetic differences between lambs. Additional studies determined the neutralization phenotype of virus isolates from alveolar macrophages of OvLV-34- or OvLV-28-infected lambs, evaluated the role of neutralizing antibodies in selection and persistence of antigenic variants, and related the severity of OvLV-induced lymphoid interstitial pneumonia (LIP) to the evolution of neutralization variants. These studies demonstrate that (i) macrophage-associated OvlV neutralization variants can arise in the presence or the absence of neutralizing antibodies directed to inoculum viruses, (ii) OvlV variants persist in macrophages in the presence of serum neutralizing antibodies, and (iii) the emergence of OvlV variants is apparently unrelated to the severity of LIP. (C) 1999 Academic Press.