Use of glutaraldehyde-fixed Escherichia coli cells as a convenient support for radioimmune assays.

Escherichia coli were activated by incubation with 1% glutaraldehyde, and the activated bacteria were then conjugated by incubation with IgG. About 66,000 molecules of IgG were bound per cell. The Escherichia coli-antibody conjugates were then used in competitive radioimmune assays. When a specific IgG fraction was used to prepare the conjugate, each cell bound about 16,000 molecules of antigen. With an antigen which had a specific activity of about 300 cpm/ng (or about 4.8 × 10⁴ cpm/pmol), the assay was linear over a range of 40–300 ng/ml (0.3–2.0 pmol/ml). About 100 samples were assayed per day.