Effect of normal plasma on the patient's APC-SR.

(A) APC-SR in samples obtained by mixing the patient's plasma with PNP. For the determination of APC resistance, a standard method has been used.20 The amount of PNP is progressively increased in the mixtures from 0% to 100%. The APC-SR remained low and 20% of the patient's plasma in the mixture is still able to determine relevant APC resistance. This suggests the presence of a strong inhibitory effect of factor Va inactivation by APC. (B) Effect of the factor V concentration on APC-SR in samples obtained by mixing plasma under investigation with factor V-deficient plasma. When PNP (filled squares) is the source of factor V, as the concentration of the molecule increases, the APC-SR progressively rises within the normal ranges. Under similar experimental conditions, the patient's plasma (filled circles) displays a very low APC-SR, which is consistent with severe APC resistance. If PNP is supplemented with an immunoglobulin preparation derived from normal individuals (filled diamonds), the APC-SR increases with increasing factor V concentrations in the mixture as shown for PNP (filled squares). When a patient's immunoglobulin preparation is used to supplement PNP instead of immunoglobulin isolated from normal individuals, the APC-SR remains markedly low even at high (normal) concentration of factor V in the mixture (filled triangles).