Immunological studies in combined factor V and factor VIII deficiency.

Plasma samples from patients with inherited combined factor V and factor VIII deficiency were examined by immunological methods for the presence of factor V and Factor VIII-related antigens. A factor V-related antigen was consistently demonstrated in all plasma samples by inhibitor neutralization assay using a non-precipitating rabbit antibody. Factor VIII-related antigens were detected by inhibitor neutralization using human antibody and by electroimmunoassay using a precipitating rabbit antibody. The amounts of factor V and factor VIII-related antigens present in the patient's samples were similar to those found in normal human plasma. The findings confirm the presence of normal levels of factor VIII-related antigen in the plasma of these patients and suggest that inactive antigenic determinants of procoagulant factor V and procoagulant factor VIII are also present. The results are consistent with the possibility that a common precursor of porcoagulant factor V and factor VIII is defective in these patients.