Changes in the immunoreactivity of Apo A-I during storage

We assayed apolipoprotein (Apo) A-I levels in re-constituted standard sera, and in serum samples and dried blood samples spotted onto filter-paper, taken from 4 healthy adults. An ELISA method was used to study changes in immunoreactivity after storage at different temperatures, for periods of up to 2 yr. For standard Apo A-I sera, immunoreactivity increased significantly with both time and temperature of storage after reconstitution. Immunoreactivity of Apo A-I in sera of healthy adults was stable on storage at -16 degrees C and -70 degrees C for 43 days, at 4 degrees C for 21 days, and at room temperature for only 10 days, after which there was a considerable increase. Dried blood spot Apo A-I immunoreactivity was also stable at -16 degrees C for at least 43 days, but not at 4 degrees C. Storage at room temperature caused significantly increased immunoreactivity from day 2. These changes could result from temperature and time-dependent structural or compositional changes in high density lipoprotein particles leading to exposure of more Apo A-I antigenic sites. The results define the conditions of time and temperature of storage of samples and standards necessary for Apo A-I assays using ELISA methodology.