HETEROGENEITY OF FACTOR-VIII ANTIBODIES - FURTHER IMMUNOCHEMICAL AND BIOLOGIC STUDIES

Abstract

Previous studies using immunoneutralization techniques showed that many factor VIII inhibitors are Ig[immunoglobulin]G antibodies of a single L chain type. This apparent homogeneity was investigated by immunoneutralization assay and liquid isoelectric focusing of inhibitor fractions from 5 hemophiliacs and 2 nonhemophiliacs. By immunoneutralization assay, inhibitors from 4 hemophiliacs and 1 nonhemophiliac were exclusively .kappa. L chain type: the 5th hemophilic inhibitor was predominantly .kappa., and the 2nd nonhemophilic inhibitor was a mixture of .kappa. and .lambda.. H chain subtyping of the 6 predominantly or exclusively .kappa. inhibitors showed all to be mixtures of IgG4 and IgG1. By isoelectric focusing, 2 inhibitors showed multiple peaks of activity between pH 5 and 9. The remaining 5 showed predominant peaks of activity, which were solely IgG.kappa., between pH 5.8 and 7, with smaller peaks between pH 7 and 9. The most acidic major peak, focusing at pH 6, was IgG4 in the 3 cases tested. Two of these acidic peaks neutralized factor VIII more efficiently than other peaks in the same focusing profiles, suggesting greater affinity for factor VIII. These studies demonstrate that factor VIII inhibitors are composed of heterogenous subpopulations of immunoglobulins which can be separated by isoelectric focusing.