Adenovirus Neutralizing Antibody Determination by Colorimetric Assay.

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Abstract
A colorimetric assay method for measuring neutralizing antibodies against adenovirus in HeLa cell tissue culture in plastic panel cups is described. In this test the serum virus antigen and HeLa cell suspension are added to a cup at one time and covered with light mineral oil. This test depends on the previously reported phenomenon that growth of adenovirus in HeLa cell cultures causes lowering of the pH of the medium below that of uninfected cultures and that specific immune serum prevents this pH effect. By quantitating the pH lowering effect of adenovirus growth in HeLa cells in relation to the serum dilution the amount of specific antibody can be determined. The reaction is standardized so that in 3 days the phenol red indicator turns yellow by unneutralized virus while the indicator turns only to red orange by the metabolism of the HeLa cells when the virus antigen is neutralized. It was shown that this colorimetric test gives titers in paired serums from human adenovirus infections with antigen types 1 through 10 which are similar or slightly higher than those obtained with a test tube method depending for reading on microscopic observation of cytopathogenesis. This method also was found suitable for typing adenoviruses.