Observations on a factor-V inhibitor.

A 67-year-old man developed a potent inhibitor of factor V shortly after undergoing blood transfusions and surgery. The inhibitor reacted in a time-dependent manner with factor V and gave a non-linear concentration graph. Studies with specific antisera indicated that it contained gamma and mu heavy chains and both kappa and lambda light chains. The plasma from two patients with congenital factor-V deficiency did not neutralize the inhibitor.