Measurement of small quantities of alpha 2-macroglobulin in cell cultures by enzyme labelled immunoassay.

We established an enzyme labelled immunoassay (EIA) for the determination of alpha 2-macroglobulin (alpha 2M). The sensitivity was high enough to measure trace amount of alpha 2M secreted into the medium of cell culture. The assay range in medium was from 2 to 140 ng/ml and the within-assay coefficients of variation (CV) were 10.1% and 6.7% at 31.2 ng/ml and 62.5 ng/ml, respectively. Between-day CV ranged from 9.3% to 15.9%. Using this method, alpha 2M was detected in the medium of a cultured human melanoma cell line. In addition, the immunoreactive alpha 2M in the medium was identified with serum alpha 2M by the method of SDS-PAGE and Western blotting. Our results indicate that the EIA method could be a useful tool for the determination of alpha 2M in cell cultured medium.