Radioimmunoassay for human plasma apolipoprotein B.

We have developed a simplified double antibody radioimmunoassay for human apolipoprotein beta. The purified antigen, a narrow density subclass of beta lipoprotein (d 1.030-1.050 g/ml; was isolated by a combination of gel filtration and ultracentrifugationmthis material gave a single immunoprecipitin arc on crossed immunoelectrophoresis into an antibody to whole human serum. The antigen was radiolabelled using iodine monochloride at pH 10. The iodinated antigen was indistinguishable immunochemically from native material and eluted as a single radioactive peak from a Sephadex G-200 column. The lower limit of sensitivity of the assay was 15 ng protein, and the working range, 15-200 ng. The mean apolipoprotein B level (+/-1 S.D.) in 128 healthy control subjects was 86.6 +/- 29.6 mg/100ml and is in agreement the values published by other workers using unmodified assays.