Comparative Study of 125I- and [3H]Acetate-Labeled Antibodies in Detecting Iridescent Viruses

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Abstract
Radioimmunoassays for detecting cell-associated or released virus are described using either 125I- or [3H]acetate-labeled antibodies. In the first assay system, antigen-antibody complexes were separated from free antibody by centrifugation. Sensitivities of 0.1 μg of iridescent virus could be achieved with either 125I- or [3H]acetate-labeled antibody. In the second assay, the antigen was fixed to cover-slip cell cultures, and then reacted with labeled antibody, unbound radioactivity being removed by repeated washing. Nonspecific binding with this method was 0.5 to 1% of the total radioactivity added and sensitivities of 0.1 or 10 μg were achieved with 125I and [3H]acetate, respectively. Immunoglobulins were labeled at the rate of 1 in 300 for 125I and 1 in 200 with [3H]acetate although there was a 400-fold greater isotopic abundance of 125I relative to 3H. The possibility of preparing labeled protein of high specific activity using carrier-free [2-3H]iodoacetic acid is discussed.

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