Anti-FX auto
antibodies in plasma were detected by ELISA with three of four cases. One case of anti-FX
autoantibody negativity was later diagnosed as
AL-amyloidosis.
IgG1 and
IgG3 coexisted in all anti-FX
autoantibodies of the three patients with AiF10D (cases X1, X2, and X3). Western blot analysis showed that the
antibodies were bound to the FX light chain for cases X2 and X3, but the binding was weak for case X1. When the fusion
proteins of a secretory
luciferase with full-length FX or its γ-carboxylated
glutamic acid (Gla) domain were added to the plasma of the three patients, both fusion
proteins were immunoprecipitated as
antigen-antibody complexes. Contrarily, the latter fusion
protein produced in the presence of
warfarin demonstrated a decrease in the collection rate, suggesting that their
autoantibodies recognized the light chain and regions containing Gla residues. Since all three patients were essentially negative for FX inhibitors, it was concluded that the anti-FX
autoantibodies for these cases were predominantly non-neutralizing. The concentration of the FX
antigen also significantly reduced in these patients, suggesting that anti-FX
autoantibodies promote the clearance of FX.
CONCLUSION: