Evidence for retroviral capsid and nucleocapsid antigens in ovine pulmonary carcinoma.

A retroviral etiology has been proposed for ovine pulmonary carcinoma (OPC); however, the putative virus (OPCV) has yet to be cultured. A Western immunoblotting assay using a panel of retroviral antisera was developed to further define the structural proteins of the virus associated with OPC and to confirm their presence in tumor samples of affected sheep. The results confirmed that the main structural viral component, the capsid protein (CA), was present in tumor materials (lung fluids, lavages, and tumor homogenates) but not in similar samples from control subjects. A second viral protein was detected in the tumor samples by antisera to the nucleocapsid protein (NC) of type D retroviruses. Both components could be purified from the tumor material in a manner consistent with association in viral particles. The cross-reactivity of the OPC antigens to other type B and D retroviruses was assessed. These results suggest that OPC antigens are closely related to the structural proteins of several type D primate retroviruses.