Abstract
A review of radioimmunoassays for measuring human apolipoprotein B (apo B), the A apolipoproteins of high density lipoprotein (apo A-I and apo A-II) and apolipoprotein C-II (apo C-II) in human plasma and in isolated lipoproteins is presented. The sensitivity, specificity and validity of each of these assays is discussed. In normolipidemic subjects the reported serum apo B concentrations ranged between 0.83 +/- 0.16 and 0.92 +/- 0.21 g per l (m +/- SD). Serum apo B concentrations were highest in Type II subjects (Type IIa homozygotes 3.83 +/- 0.43 g per l; Type IIa heterozygotes 2.37 +/- 0.47 g per l) and were less elevated in patients with Type IV and Type V disorders (1.32 +/- 0.21 g per l and 1.26 +/- 0.30 g per l, respectively). Preliminary data on the relationship between plasma apo B and cholesterol, the distribution of apo B amongst the lipoprotein classes and a comparison of the lipoprotein lipid-apo B ratios in the various hyperlipidemic disorders are summarized. In contrast to apo A-II, the immunoreactivity of apo A-I was not fully exposed in whole sera and in isolated lipoproteins. The different methods used to measure the apo A-I immunoreactivity are discussed. In normolipidemic subjects the serum apo A-I concentration in males and females was 1.13 +/- 0.061 and 1.24 +/- 0.068 g per l (m +/- SD), respectively, while the corresponding serum apo A-II values were 0.35 +/- 0.038 g per l and 0.41 +/- 0.046 g per l. In subjects with Tangier's disease, the serum apo A-I and apo A-II concentrations were less than 1 percent and 5 to 7 percent of that found in controls. The serum apo A-I level was also reduced in two subjects with abetalipoproteinemia (0.38 g per l and 0.30 g per l) and Tye II hyperlipoproteinemia (range 0.54 to 0.86 g per l). In normotriglyceridemic subjects and those with Type IIa hyperlipoproteinemia, the total plasma apo C-II concentrations were 0.0497 +/- 0.0040 g per l and 0.0562 +/- 0.0054 g per l (m +/- SE). Plasma apo C-II levels in Type IIb, Type IV and Type V lipoproteinemic subjects were 0.0899 +/- 0.0046, 0.0854 +/- 0.0069 and 0.1328 +/- 0.0021 g per l, respectively and were significantly higher than in the normotriglyceridemic subjects. An analysis of the relationship between the apo C-II content and the lipoprotein lipase activator properties of VLDL isolated from normo- and hypertriglyceridemic plasma samples is presented.
