Immunochemical characterization of antibodies to factor VIII in hemophilic and nonhemophilic patients.

Plasma samples from eighteen patients (9 hemophilic, 9 nonhemophilic) with antibodies to Factor VIII were purified by protein A gel chromatography. This procedure separates the IgG3 from the IgG1, IgG2, and IgG4 subclasses. The partially purified anti--Factor VIII fractions were typed for their heavy and light chain composition by immunoneutralization assay. Residual anti--Factor VIII activity was revealed by inhibition of fibrin formation in agarose gel plates. The combination of these two techniques permitted the study of a relatively large number of partially purified samples, at several dilutions of each, against each anti-heavy or anti-light chain antiserum obtained from various sources. A high degree of subclass and light chain restriction was found in the antibodies from the hemophilic patients, eight were predominantly of IgG4 kappa type, the ninth was IgG4 but of mixed light chains. In contrast, a heterogeneous distribution was found in the ten nonhemophilic patients: two IgG4 kappa, one IgG4 lambda, one IgG4 with both kappa and lambda, two a mixture of IgG1 and IgG4 with only kappa light chains, and three a mixture of IgG1 and IgG4 as well as both light chains.