Immunochemical conditions affecting the measurement of DNA antibodies using ammonium sulfate precipitation

Open Access
Publisher Website
Google Scholar
Abstract
The binding of serum to native DNA as detected by the Farr ammonium sulfate technic is subject to considerable variation dependent on reaction conditions. DNA‐binding activity of normal sera was significantly increased in buffers of low pH or ionic strength, to the range of SLE sera. Conversely, without incubation at 37 C and 4 C, many SLE sera were within the normal range. Serum nuclease activity did not account for the absence of DNA‐binding in normal sera. The presence or absence of serum complement did not affect binding. Both precipitating and nonprecipitating antibodies are detected using ammonium sulfate precipitation. Optimal conditions for specificity and sensitivity included use of a buffer of pH 8 with conductivity of 12.5 millimhos (equivalent of 0.15M sodium chloride), and incubation for one hour at 37 C and 24 hours at 4 C prior to addition of saturated ammonium sulfate.