Heterogeneity of human factor V deficiency. Evidence for the existence of antigen-positive variants.

Functional human Factor V has been purified using a rapid immunoaffinity method. Following barium citrate adsorption of plasma, Factor V was precipitated with polyethylene glycol at a concentration between 5 and 14%. The resulting preparation was applied to a column containing an immobilized immunoadsorbent consisting of an IgG fraction containing a naturally occurring human monoclonal (IgG(4)lambda) antibody with inhibitory activity against human Factor V. The solid phase immunoglobulin quantitatively bound Factor V from human plasma. The bound Factor V was effectively eluted with a Tris buffer pH 7.2 containing 1.2 M NaCl and 1 M alpha-methyl-D-mannoside. The isolated native Factor V with high specific activity (92 U/mg) showed a single band (M(r), 350,000) on both reduced and nonreduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Factor V was purified 5,100-fold over plasma with an overall yield of 77%. The purified Factor V when subjected to thrombin activation exhibited an 18-fold increase in coagulant activity. The isolated Factor V neutralized the inhibitory activities of the monoclonal antibody that was used to purify it, as well as the rabbit antibodies produced by immunizing the animals with the purified Factor V. Immunoelectrophoresis of purified Factor V against the polyclonal rabbit antiserum resulted in a single precipitin arc of identical mobility to the Factor V in normal human plasma. Analysis by double immunodiffusion showed a line of identity between plasma and purified Factor V and crossed immunoelectrophoresis showed a single species in normal plasma.A competitive enzyme-linked immunosorbent assay using the rabbit antibody against Factor V was applied to quantify Factor V antigen level in human plasma. Reconstitution of congenitally deficient or immunodepleted plasma with normal plasma or purified Factor V gave parallel dose-response curves. In 14 normal plasma the coagulant activity was 0.98+/-0.02 U/ml (mean+/-SEM) and antigen concentration was 11.1+/-0.4 mug/ml. A pool of 14 patients with congenital Factor V deficiency were studied. 10 patients had Factor V antigen ranging from 1.0 to 2.4 mug/ml with corresponding coagulant activities (0-0.17 U/ml) indicating a low concentration of normal Factor V, presumably due to decreased synthesis or increased degradation. When these patient plasmas and the normal plasmas were analyzed together an excellent correlation (r = 0.97, P < 0.01) was obtained. However, four patients with coagulant activity (0-0.08 U/ml) had Factor V antigen concentrations ranging from 4.4 to 6.1 mug/ml, indicating the presence of a reduced concentration of abnormal Factor V protein. The presence of patients with antigen similar in concentration to coagulant activity and antigen in excess of Factor V activity indicates the heterogeneity of congenital Factor V deficiency.