Affinity chromatography
An Agilent Technologies (Santa Clara, CA, USA) Multiple Affinity Removal Column Human 14 (Cat No 5188-6557) was used in the affinity chromatography, according to the manufacturer’s instructions. Samples were diluted four-fold with buffer A. Fourteen proteins and their complexes (i.e. ‘high-abundance proteins’) were retained in the column: albumin, IgG, IgA, transferrin, haptoglobin, antitrypsin, fibrinogen, alpha2-macroglobulin, alpha1-acid glycoprotein, IgM, apolipoprotein AI, apolipoprotein AII, complement C3 and transthyretin. Low-abundance proteins were collected as a flow-through fraction. High-abundance proteins were eluted with buffer B and collected.