Abstract
Evidence for the presence of circulating immune complexes was found in thirty-four out of fifty-five samples from forty-seven patients with haemophilia A. In eleven patients the complexes, precipitated from the blood with polyethylene glycol, were digested with pepsin. The F(ab')2 antibody was tested, and found to have neutralizing activity against coagulant Factor VIII in two patients. In one of these no free antibody had ever been found in the plasma, while in the other the antibody was concentrated tenfold in the complex. In two other samples free without complexed antibody was found. In comparison, IgG-containing complexes were found in nine out of nineteen patients with von Willebrand's disease and no complexes were found in the sera from twelve multi-transfused thalassaemics. PEG precipitation is a useful technique for the preparation of concentrated immune complexes for further study such as antigen identification.