Crossed immunoelectrophoresis of purified APC (A) or protein C in plasma (B) in the presence of control or patient’s IgG. Polyclonal rabbit antihuman protein C antiserum was used for detection of either APC or protein C as described in Materials and Methods. (A) Electrophoresis of 20 μL TBS-BSA containing 150 ng APC and 200 μg of control IgG (1) or patient’s IgG (2). (B) Electrophoresis of 10 μL of patient’s plasma (1), a mixture of 10 μL of normal plasma (40 ng protein C), and 10 μL of normal IgG (140 μg) (2) or 10 μL of normal plasma and 10 μL (140 μg) patient’s IgG (3).