Quantitative immunoassay of adenosine deaminase in combined immunodeficiency disease.

We have developed a quantitative immunoassay for the measurement of human adenosine deaminase that requires neither purified enzyme nor monospecific antibody. With this technique, cultured fibroblasts from three immunodeficient patients were shown to contain adenosine deaminase as detected both catalytically and immunochemically. In one patient the level of immunoreactive enzyme exceeded the amount of catalytically active adenosine deaminase, suggesting a structural alteration in the enzyme molecule.