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

Abstract

Radioimmunoassays for detecting cell-associated or released virus are described using either 125 I- or [ 3 H]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 125 I- or [ 3 H]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 125 I and [ 3 H]acetate, respectively. Immunoglobulins were labeled at the rate of 1 in 300 for 125 I and 1 in 200 with [ 3 H]acetate although there was a 400-fold greater isotopic abundance of 125 I relative to 3 H. The possibility of preparing labeled protein of high specific activity using carrier-free [2- 3 H]iodoacetic acid is discussed.