Immunoglobulin G depletion from human serum with metal-chelated beads under magnetic field

Magnetic poly(ethylene glycol dimethacrylate-N-methacryloyl-(l)-histidine methyl ester) [mag-poly(EGDMA-MAH) beads, 50-100 μm in diameter, were produced by suspension polymerization for affinity depletion of immunoglobulin G (IgG) from human serum. Cu²⁺ ions were complexed directly via MAH groups (Cu²⁺ loading: 4.1 μmol/g). IgG depletion studies were performed by magnetically stabilized fluidized bed column. Acetate, Tris-HCl, MES and phosphate buffers all allow adsorption of similar quantities of IgG (27.3-45.6 mg/g). MOPS and HEPES allow higher adsorption quantities (79.6 mg/g and 74.1 mg/g, respectively). Maximum adsorption capacities in MOPS buffer were 46.8 mg/g for mag-poly(EGDMA-MAH) and 102.1 mg/g for Cu²⁺ chelated mag-poly(EGDMA-MAH) beads. The adsorption capacity decreased drastically from 102.1 mg/g to 30.7 mg/g with the increase of the flow rate from 0.2 ml/min to 3.5 ml/min. The elution studies were performed by 1.0 M NaCl. The elution results demonstrated that the adsorption of IgG to the adsorbent was reversible. To test the efficiency of IgG depletion from human serum, proteins in the serum and eluted portion were analyzed by two-dimensional gel electrophoresis. The depletion efficiency for IgG was above 99.4%. Eluted proteins include mainly IgG, and a small number of non-albumin proteins such as apo-lipoprotein A1, sero-transferrin, haptoglobulin and α1-antitrypsin. When anti-HSA-sepharose adsorbent is used together with our metal-chelated mag-beads, IgG and HSA can be depleted in a single step.