A variant very-low-density lipoprotein was associated with severe hypertriglyceridaemia. Urea-polyacrylamide gel electrophoresis of the tetramethylurea-soluble apolipoproteins of these very-low-density lipoproteins (VLDL) showed that the apolipoprotein C-II content was less than 10% of that in VLDL from hypertriglyceridaemic (3-120 mmol/l) controls. 2. VLDL were incubated with bovine milk lipoprotein lipase (LPL) and a 9,10-3H-labelled triglyceride emulsion. The VLDL deficient in apolipoprotein C-II were a poor activator of LPL, compared with the effect of VLDL with normal content of apolipoprotein C-II obtained from either normal or hypertriglyceridaemic sera. 3. The efficacies of various VLDL as substrates fo activated LPL were examined. Apolipoprotein C-II-deficient VLDL were a poor substrate for the activated enzyme compared with normal or hypertriglyceridaemic VLDL, and compared wtih an artificial triglyceride emulsion. 4. The abnormal VLDL were obtained from a subject with an IgG3 lambda myeloma protein. Intravenous infusion of normal plasma containing apolipoprotein C-II was followed by rapid, complete, but short-lived (5-10 days) clearance of serum triglyceride. The effect was observed on three occasions until treatment of the myeloma was effective. 5. The monoclonal protein behaved as a cryoglobulin, and formed large particle complexes with triglyceride-rich lipoproteins, especially at temperatures below 37 degrees C. The apolipoprotein C-II deficiency, and consequent hypertriglyceridaemia, may be secondary to an autoantibody directed against apolipoprotein C-II. VLDL from relatives with hypertriglyceridaemia, but without myeloma, had normal apolipoprotein content, activated LPL, and were efficient substrates for the enzyme.
