Factor XI (F11, FXI) is a coagulation protein produced in the liver that circulates in plasma at approximately 5 ug/ml (30 nM). The mass of FXI is 160 kDa as determined by SDS-PAGE under nonreducing conditions and 80 kDa upon reduction. FXI consists of two identical 80 kDa subunits linked by disulphide bonds. Each subunit consists of a tandem repeat of four apple domains followed by a serine protease catalytic domain. Cleavage of FXI by activated factor XII or thrombin converts each subunit into a two-chain form and generates two active sites per FXIa molecule. The mass of FXIa is 160 kDa unreduced, but upon reduction FXIa migrates as a heavy chain of 50 kDa and a light chain of 30 kDa. The catalytic site of FXIa resides in the light chain. In plasma, FXI or FXIa circulates in non-covalent 1:1 complex with high molecular weight kininogen, which acts as a cofactor in the activation of FXI by activated factor XII. The activity of FXIa is regulated by platelets and by several proteinase inhibitors including, in order of decreasing importance, C1-inhibitor, alpha-2-antiplasmin, alpha-1-antitrypsin and antithrombin. Heparin has relatively little effect on the rate of inhibition of FXIa by antithrombin. The only known natural substrate for activated FXI (FXIa) is factor lX (Christmas factor) and the only cofactor required for this reaction is ionized calcium1-3.
1. Wuillemin WA, Minnema M, Meijers JCM, Roem D, Erenberg AJM, Nuijens JH, ten Cate H, Hack EC; Inactivation of Factor XIa in Human Plasma Assessed by Measuring Factor XIa-Protease lnhibitor Complexes: Major Role for Cl-lnhibitor. Blood 85:1517, 1995.
2. DeLa Cadena R, Watchtfogel YT, Colman RW, in Hemostasis and Thrombosis, 3d Edition, eds. RW Colman, J Hirsh, VJ Marder and EW Salzman, pp. 219-240, J.B. Lippincott Co., Philadelphia, 1994.
3. Baglia FA, Seaman FS, Walsh, PN; The Apple l and 4 domains of Factor XI Act to Synergistically Promote the Surface-Mediated Activation of Factor XI by Factor XIIa. Blood 85:2078, 1995.
VisuLizeâ„¢ Factor XI Antigen ELISA kit is for Research Use Only and must not be used for diagnostic applications.
Rapid sandwich ELISA to measure Factor XI antigen (FXI:Ag)
2 hour total incubation time
FXI:Ag reported as Units/ml traceable to ISTH SSC standard for FXI activity
Includes normal and low control
Intra-assay precision: 4.5 %
Inter-assay precision: 1.1 %
Quantification of Factor XI in plasma
Pre-coated plate in a convenient 6×16 well format
Calibrator plasma, Control A and Control B plasmas (2 vials of each)
Sample diluent and wash buffer concentrate
Ready-to-use detecting antibody, TMB substrate and stop solutions
VisuLize FXI Antigen ELISA Kit
ELISA Kits:Â FVIII-AG – VisuLize FVIII Antigen Kit, FIX-AG – VisuLize FIX Antigen Kit, TAFI-AG – VisuLize TAFI Antigen Kit
Antibodies:Â GAFXI-IG – goat anti-human FXI, whole IgG from serum, 10mg vial; GAFXI-AP – goat anti-human FXI, affinity purified IgG, 0.5mg vial; GAFXI-HRP – goat anti-human FXI, peroxidase conjugated IgG, 0.2mg vial; GAFXI-APFTC – goat anti-human FXI, affinity purified, FITC conjugated IgG, 0.1mg vial; GAFXI-APBIO – goat anti-human FXI, affinity purified, biotinylated IgG, 0.1mg vial; SAFXI-IG – sheep anti-human FXI, whole IgG from serum, 10mg vial; SAFXI-AP – shep anti-human FXI, affinity purified IgG, 0.5mg; FXI-EIA – matched pair antibodies for ELISA of human FXI, sufficient reagents for 4×96 well plate
Plasma:Â FXI-DP – Factor XI deficeint plasma – citrated plasma, immune depleted of FXI, 1ml to bulk; INH11-DP – Factor XI Inhibitor Plasma, available in various activities (recorded as BU/mL) 1ml to bulk; INH11-LDP – lyophilized Factor XI Inhibitor plasma, available in various activities (recorded as BU/mL) 1ml to bulk