The antiviral effects of recombinant ovine interferon-τ (roIFN-τ) were studied in 26 lambs inoculated with ovine lentivirus (OvLV) or mock-infected. Six of the OvLV-infected lambs and three of the mock-infected lambs were treated with 106 antiviral units (AVU) per kg roIFN-τ daily for 30 days starting at day 0 post-inoculation (p.i.) and twice a week thereafter (early treatment). Six of the OvLV-infected lambs and three of the mock-infected lambs were treated with 106 AVU/kg roIFN-τ daily for 30 days starting at day 150 p.i. and twice a week thereafter (late treatment). Six OvLV-infected and two mock-infected lambs were treated either early or late with placebo. Cell-associated viraemia was quantified by an end-point dilution method. The weekly antibody response against OvLV proteins was studied by ELISA. All experimental animals were killed at 27 weeks p.i. and histological sections of lung were scored for the degree of lymphoid interstitial pneumonia (LIP). A 90 reduction in OvLV titres was detected at 4 weeks post-treatment in lambs that received early roIFN-τ treatment (P < 0.01). Differences in virus titres were also found at weeks 2 and 6 (P < 0.05). Scores for LIP degree were higher in infected lambs treated with placebo or late roIFN-τ than in the mock-infected lambs or in the infected lambs that received early roIFN-τ (P < 0.05). LIP scores were not different between mock-infected lambs and infected lambs that received early roIFN-τ. These results indicate that roIFN-τ curtails OvLV replication in vivo and reduces the likelihood of development of lentivirus-induced LIP when infected lambs are treated during the initial phases of OvLV infection.
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