- Factor B will be quantified using a monoclonal capture antibody P21/15 which recognizes an epitope present on factor B and Ba and a biotinylated rabbit anti-Bb as a detection antibody. For measurement of Ba, plasma will be depleted of factor B using Biomag magnetic beads coupled to an anti-B/Bb antibody (mAb M13/12), followed by Ba quantification using an anti-B/Ba antibody (mAb P21/15) as a capture antibody and a biotinylated antibody specific for an epitope on B/Ba (mAb M20/6) as a detection antibody.