Carbodiimide-Induced Bentonite-Antigen Complexes: Readily Prepared Immunoadsorbents

Summary γ-globulin and albumin are bound to bentonite by l-ethyl-3-(3-dimethylaminopropyl) carbodiimide. The reaction proceeds promptly at room temperature in physiologic solution. It is suggested than an organometallic bond results between protein and bentonite. The bond is stable under most conditions, and the resulting materials function well as immunoadsorbents. Rabbit antibody, isolated from the adsorbent, contains a trace of albumin and less than 1 part/1000 antigen. At equivalence, 92 to 97% of the protein in preparations of isolated antibody is precipitated by soluble antigen. Protein is adsorbed both to immunologically specific and non-specific sites on the antigen-bentonite complex. About 0.17 mole antibody is quantitatively bound per mole adsorbent antigen. In excess antibody, the capacity of the γ-globulin adsorbent exceeds 0.54 mole antibody per mole adsorbent antigen. Most antibody, in the presence of other serum protein, is bound to specific sites on the adsorbent and is readily eluted at pH 2.5. Normal γ-globulin and other proteins are bound to nonspecific sites, and remain largely bound at the pH of elution. It is likely that a small amount of antibody is bound to nonspecific, adsorbent sites and remains bound during elution. Nevertheless, estimates of serum antibody with the adsorbents exceed estimates made by quantitative precipitation and more accurately reflect total serum antibody.