Summary
We have produced a panel of ten monoclonal antibodies specific to coagulation factor
XI. Western blot analysis demonstrates that 9 of these antibodies react with the heavy
chain of factor XI and one with the light chain. Seven of these antibodies inhibit
factor XI and factor XIa activity.
We have used immobilised monoclonal antibody for the production of factor XI deficient
plasma and to purify factor XI to homogeneity with high yield in a simple two-step
procedure. These monoclonal antibodies were used to develop highly sensitive immunoassays
capable of detecting less than 0.01 u factor XI antigen ml−1. A strong correlation was found between antigen and activity levels in 11 patients
with hereditary deficiency indicating that none was cross-reacting material positive.
Cultured Hep G2 cells were found to synthesize small amounts of factor XI antigen
and this could also be detected by functional assay and by western blot analysis.