Factor XIII

June 29 and 30, 2006
Oslo Kongressenter, Norway

Chair: R. Ariens
Co-Chairs: A. Ichinose, H. Kohler, M. Maurer, R. Seitz.
Active Members: L. Muszbek, A. Inbal, V. Ivaskevicius

Session I: Vascular biology. Ikuro Maruyama ( Japan ) discussed the role of nuclear DNA binding protein HMGB1, which is found intracellularly as well as in the circulation, in inflammation and multiple organ failure during sepsis. Recent data show and effect of HMGB1 on several coagulation parameters, amongst which FXIII. HMGB1 competes with thrombin for thrombomodulin binding and increases FXIII activation. Aida Inbal ( Israel ) presented data on the role of FXIII in angiogenesis and wound healing. Experimental models in FXIII knockout mice show reduced angiogenesis and wound healing. Reconstitution with FXIII restores these defects effectively.

Session II: Registry and standardisation. Vystas Ivaskevicius ( Germany ) presented the first International Registry on FXIII mutations and deficiency. The registry currently lists data from 105 patients with FXIII deficiency, including mutations in both FXIII A- and B-subunit, and details on phenotypic presentation. A website for the registry that includes submission forms and where information on the mutations can be found has been set up at www.f13-database.de. Currently most data are from patients from Europe , and submissions from the rest of the world including less developed countries are encouraged. Sanj Raut ( UK ) presented an update on current standardisation activities of FXIII. Data from the addendum report on assignment of antigen level to the 1 st International plasma Standard for FXIII was presented. The report has been approved by the SSC, FXIII SWG (standard working group) and expert reviewers. Approval will be sought from the Business meeting to submit the report to the WHO. Protocols for an International collaborative study for the development of a standard for FXIII concentrate were presented. It is currently discussed which assays should be included in this study. Akitada Ichinose ( Japan ) presented an overview of the history of the FXIII standard working group, which he chairs. Issues regarding formation of rFXIII-A complexes with B in plasma were discussed in light of eventual need for a standard for rFXIII-A. Dr Ichinose expressed concerns regarding acknowledgement and financial support for the contribution of academics and scientists (who are funded by research and government grants) involved in the standardisation processes.

Session III: Measurements. Muriel Maurer ( USA ) presented an overview of current methodologies available to transglutaminase scientists for the measurement if these enzymes. Sensitivity and specificity of the various assays, including spectrophotometric methods, radioactive labelling, biotin/streptavidin systems, fluorescence and phage displays were discussed. Suitability for high-throughput strategies (low volume, suitability to multiwell plates) were also discussed. Dr Maurer suggested that future assay systems may be developed that make use of mass spectrometric or NMR technologies. Janos Kappelmayer ( Hungary ) discussed data using flow-cytometry that showed the presence of FXIII-A in the blast cells of monocytic and myelomonocytic origin in patients with acute myeloid leukemia and acute lymphoblastic leukaemia (ALL). Sixty percent of ALL cells stained positive for FXIII-A. Data were confirmed by western blots and ELISA and suggest that FXIII-A may be a useful marker in the diagnosis of ALL. Rainer Seitz ( Germany ) discussed data from a fluorescent isopeptidase assay. The assay is based on the release of a quencher by transamidase activity. The quencher is released from a synthetic peptide that is based on the sequence of alpha2-antiplasmin, a specific substrate for FXIII. Data were shown on the Km and kcat values for FXIII in plasma and FXIII/fibrinogen mixtures. The assay has a low detection limit and shows linearity with other activity assays.

Session IV: Regulation of FXIII. Hans Kohler ( Switzerland ) discussed preliminary data from a novel ELISA assay designed to measure the activation peptide of FXIII. In plasma, the FXIII AP signal increases within minutes from the addition of thrombin with concomitant decrease of the A2B2 tetramer signal. FXIII AP was also detected in serum. The assay system will be further characterised with regards to specificity and sensitivity. Laszlo Muszbek ( Hungary ) discussed novel data on the degradation of FXIII by proteases (cathepsin G, elastase) released by polymorphonuclear cells in the clot. Elastases degraded FXIII within 3 hours, alomg with fibrin degradation which also occurs by the same enzymes. The degradation was reversed by specific inhibitors of these enzymes. Helen Philippou ( UK ) showed novel data on the degradation of FXIII by plasmin. This degradation was found to be dose- and time-dependant, reversed by alpha2-antiplasmin, occurred mainly with activated FXIII, was enhanced by fibrin and was shown to occur in plasma clots. The degradation of FXIII by plasmin preceded lysis of the clots. Clots from plasminogen depleted plasma did not show FXIII degradation.