Process for therapeutic dissociation of immune complexes and removal of antigens

The present invention provides an improved method for treating blood to remove foreign substances such as immune complexes and free antigen. This is advantageously accomplished by separating a portion of a patient's blood as plasma, and acidifying the plasma to a pH below about 3.1 in order to cause the immune complexes to dissociate into antigen and antibody. After removing the antigen, the plasma is returned to the patient. Preferably, the patient's blood is substantially diluted prior to plasma separation, thereby substantially increasing the clearance rate of the plasma separator device and also washing off antigens bound to cellular blood components. Also, it is preferred that the plasma fraction is further diluted during the acidification step. Subsequent removal of excess fluid will cause substantial removal of free antigen. In a presently preferred process, the excess fluid volume is reduced by use of an ultrafiltration device capable of passing antigen, but not larger protein constituents of plasma. The resultant plasma solution is advantageously subjected to dialysis to simultaneously remove remaining antigen and to raise the pH back to a physiological level.