An amplified immunoperoxidase assay to detect bovine leukemia virus expression: development and comparison with other assays.

An amplified immunoperoxidase (AIP) assay using an avidin:biotin complex was developed to detect bovine leukemia virus (BLV) antigen expression in lymphocytes which had been cultured 24 h and fixed with acetone. Nonspecific reactions were eliminated by absorbing the test serum with 100% horse or cow serum. DNA synthesis inhibition did not decrease the number of AIP-positive cells, and there were no apparent preferential losses of major lymphocyte subpopulations during culture. Both viable and nonviable BLV-expressing cells were detected. Thus, the number of AIP-positive cells seems to be a good estimate of the minimum number of infected lymphocytes present in the uncultured blood cells. In direct comparisons, twice as many BLV-expressing cells were detected with the AIP assay as with an indirect immunofluorescence test. The AIP assay is as sensitive as the syncytia infectivity assay and only slightly less sensitive than an immunoperoxidase infectivity assay for detecting BLV-infected lymphocytes in the blood of infected cattle that were in early stages of infection and/or had low titers of antiviral antibodies. The AIP assay is the most sensitive, rapid, and reproducible procedure available for the identification of individual cells infected with BLV. This assay may be of great value in studies on the biology of BLV infection.