APOB and systemic lupus erythematosus: Serum cholesterol ester transfer protein (CETP) activity, which decreases HDL levels by preferentially transferring cholesterol esters from HDL to apoB-containing LDL, was higher in SLE patients than in HCs (38.4% ± 6.8% vs. 34.2% ± 2.6%, p = 0.03) (Fig. 1b).