Effect of anti-II MoAb and LA IgGs on the KCT of normal plasma. (A) A control MoAb or anti-II MoAb was added to an equal volume of normal plasma and the KCT was determined.14 The normal plasma was depleted of IgG using protein G sepharose. The anti-II MoAb prolonged the KCT of normal plasma in a concentration-dependent manner, whereas the control MoAb had no effect. (B) To confirm the LA activity of the IgG preparations from the 7 patient plasmas, they were added to an equal volume of normal plasma and the KCT was determined.14 The normal plasma was depleted of IgG using protein G sepharose. Values for LA IgGs are expressed as a proportion of the KCT for normal plasma, with values greater than 1.2 (indicated by a horizontal line) being positive for LA. Control values were combined and are expressed as the mean ± SE (n = 5). The IgG prepared from control subjects’ serum showed no LA activity at the concentrations tested, whereas all of the patients’ IgGs resulted in prolongation of the KCT at final concentrations of 20 μmol/L and greater.