To better define the relationship between ovine lentivirus (OvLV) infection and respiratory disease, pulmonary leukocytes and postmortem lung specimens from 42 sheep seropositive or at risk for OvLV infection were obtained. The lungs were examined for lesions of lymphoid interstitial pneumonia (LIP), and animals were categorized into five groups by severity of LIP and OvLV serologic status. The presence of OvLV in alveolar macrophages was established by proviral DNA amplification using the polymerase chain reaction (PCR), and the proportion of infected cells was determined by a quantitative focal immunoassay (FIA) and by immunohistochemistry. The concentration of OvLV p25 in serum was measured by capture ELISA. In contrast to animals with mild or no pulmonary lesions, sheep with moderate or severe LIP (17/42) were all seropositive, 71% had antigenemia (greater than 2 ng/mL), and 82% had proviral DNA in 1.5 x 10(5) alveolar macrophages. Of sheep positive by PCR, those with moderate or severe LIP (79%) had an average of 3 infected cells/10(3) alveolar macrophages by FIA. These results implicate alveolar macrophages as important target cells in the pathogenesis of OvLV-induced respiratory diseases.

Monoclonal antibodies (MAbs) directed against two phenotypically distinct ovine lentivirus (OvLV) strains were generated by fusion of BALB/c SP2/0-Ag 14 myeloma cells with spleen cells from mice immunized with purffied OvLV. Hybridomas were selected by indirect enzyme-linked immunosorbent assay (ELISA) and analysis of reactivity on immunoblots. The majority (17 of 21) of the MAbs recognized the gag-encoded capsid protein, CA p27, of both strains. Four other MAbs recognized a smaller structural protein, presumably a matrix protein, MA p17. Three distinct epitopes on CA p27 and one on MA p17 were distinguished by the MAbs with competition ELISA. MAbs from each epitope group were able to recognize 17 North American field isolates of OvLV and the closely related caprine arthritis-encephalitis virus (CAEV). Analysis of the data indicated that these epitopes were highly conserved among naturally occurring isolates. A representative MAb from each epitope group of anti-CA p27 MAbs reacted with four field strains of OvLV and CAEV on immunoblots. An anti-MA p17 MAb recognized the same OvLV strains on immunoblots but failed to recognize CAEV. MAbs which recognize conserved epitopes ofgag-encoded lentivirus proteins (CA p27 and MA p17) are valuable tools. These MAbs can be used to develop sensitive diagnostic assays and to study the pathogenesis of lentivirus infections in sheep and goats.

A focal immunoassay and an antigen-capture enzyme-linked immunosorbent assay (antigen-capture ELISA) were developed to quantify infectious ovine lentivirus (OvLV) and OvLV capsid protein (CA) (p27), respectively. The in vitro kinetics of replication and cytopathogenicity of distinct biological clones of OvLV (rapid/high and slow/low phenotypic variants) were assessed. Both viruses were detected by focal immunoassay within 48 h postinfection, 2 days before syncytia were observed in goat synovial membrane cells infected with rapid/high OvLV and 4 days before they appeared in cultures infected with slow/low OvLV. CA was first detected by antigen-capture ELISA in supernatants of cells infected with rapid/high OvLV 4 days postinfection, and it reached a plateau by 10 days, 4 days after peak syncytium formation. In contrast, in cultures infected at the same multiplicity of infection with slow/low OvLV, CA was detected 8 days postinfection, and the titer gradually increased over the following 12 days while the number of syncytia gradually decreased. Peripheral blood mononuclear cells (PBMC) from seropositive sheep treated with phorbol 12-myristate 13-acetate (PMA) generally expressed CA earlier and at higher levels than PBMC treated with either phytohemagglutinin or concanavalin A. Serum CA levels above 3 ng/ml were found in 58% (18 of 31) of seropositive sheep. However, there was no correlation between PMA-induced CA expression and levels of antigenemia. Viral heterogeneity may account for variations both in CA expression in cultures of PBMC and in antigenemia, humoral immune response, and viral pathogenicity in infected animals.