Magnetic Resonance Imaging Reveals Distinct Roles for Tissue Transglutaminase and Factor XIII in Maternal Angiogenesis During Early Mouse Pregnancy.

OBJECTIVE: The early embryo implantation is characterized by enhanced uterine vascular permeability at the site of blastocyst attachment, followed by extracellular-matrix remodeling and angiogenesis. Two TG (transglutaminase) isoenzymes, TG2 (tissue TG) and FXIII (factor XIII), catalyze covalent cross-linking of the extracellular-matrix. However, their specific role during embryo implantation is not fully understood. Approach and Results: For mapping the distribution as well as the enzymatic activities of TG2 and FXIII towards blood-borne and resident extracellular-matrix substrates, we synthetized selective and specific low molecular weight substrate analogs for each of the isoenzymes. The implantation sites were challenged by genetically modifying the trophoblast cells in the outer layer of blastocysts, to either overexpress or deplete TG2 or FXIII, and the angiogenic response was studied by dynamic contrast-enhanced-magnetic resonance imaging. Dynamic contrast-enhanced-magnetic resonance imaging revealed a decrease in the permeability of decidual vasculature surrounding embryos in which FXIII were overexpressed in trophoblast cell. Reduction in decidual blood volume fraction was demonstrated when either FXIII or TG2 were overexpressed in embryonic trophoblast cell and was elevated when trophoblast cell was depleted of FXIII. These results were corroborated by histological analysis. CONCLUSIONS: In this study, we report on the isoenzyme-specific roles of TG2 and FXIII during the early days of mouse pregnancy and further reveal their involvement in decidual angiogenesis. Our results reveal an important magnetic resonance imaging-detectable function of embryo-derived TG2 and FXIII on regulating maternal angiogenesis during embryo implantation in mice.Visual Overview: An online visual overview is available for this article.

Advances of Coagulation Factor XIII.

OBJECTIVE: To provide a comprehensive literature review on roles of coagulation factor XIII (FXIII) in coagulation, wound healing, neoplasm, bone metabolism, and pregnancy. DATA SOURCES: All articles in PubMed with key words "Coagulation factor XIII", "wound", "leukemia", "tumor", "bone," and "pregnancy" with published date from 2001 to 2016 were included in the study. Frequently cited publications before 2000 were also included. STUDY SELECTION: We reviewed the role of FXIII in biologic processes as documented in clinical, animal, and in vitro studies. RESULTS: FXIII, a member of the transglutaminase (TG) family, plays key roles in various biological processes. Besides its well-known function in coagulation, the cross-linking of small molecules catalyzed by FXIII has been found in studies to help promote wound healing, improve bone metabolism, and prevent miscarriages. The study has also shown that FXIII concentration level differs in the blood of patients with leukemia and solid tumors and offers promises as a diagnostic indicator. CONCLUSIONS: FXIII has many more biologic functions besides being known as coagulation factor. The TG activity of FXIII contributes to several processes, including wound healing, bone extracellular matrix stabilization, and the interaction between embryo and decidua of uterus. Further research is needed to elucidate the link between FXIII and leukemia and solid tumors.

Free factor XIII activation peptide (fAP-FXIII) is a regulator of factor XIII activity via factor XIII-B.

In a factor XIIIa (FXIIIa) generation assay with recombinant FXIII-A2 (rFXIII-A2 ) free FXIII activation peptide (fAP-FXII) prolonged the time to peak (TTP) but did not affect the area under the curve (AUC) or concentration at peak (CP). Addition of recombinant factorXIII-B2 (rFXIII-B2 ) restored the characteristics of the FXIIIa generation parameters (AUC, TTP and CP) to those observed for plasma FXIII (FXIII-A2 B2 ). FXIII-A2 B2 reconstituted from rFXIII-A2 and rFXIII-B2 showed a similar effect on AUC, TTP and CP in the presence of fAP-FXII as observed for plasma FXIII-A2 B2 , indicating a role for FXIII-B in this observation. An effect of fAP-FXIII on thrombin, the proteolytic activator of FXIII, was excluded by thrombin generation assays and clotting experiments. In a purified system, fAP-FXIII did not interfere with the FXIIIa activity development of thrombin-cleaved rFXIII-A2 (rFXIII-A2 ') also excluding direct inhibition of FXIIIa. However, FXIIIa activity development of FXIII-A2 'B2 was inhibited in a concentration-dependent manner by fAP-FXIII, indicating that an interaction between AP-FXIII and FXIII-B2 contributes to the overall stability of FXIII-A2 'B2 . In addition to its well-known role, FXIII-B also contributes to FXIII-A2 B2 stability or dissociation depending on fAP-FXIII and calcium concentrations.

Transglutaminase factor XIII promotes arthritis through mechanisms linked to inflammation and bone erosion.

Rheumatoid arthritis is a chronic inflammatory disease characterized by synovial hyperplasia, inflammatory cell infiltration, irreversible cartilage and bone destruction, and exuberant coagulation system activity within joint tissue. Here, we demonstrate that the coagulation transglutaminase, factor XIII (fXIII), drives arthritis pathogenesis by promoting local inflammatory and tissue degradative and remodeling events. All pathological features of collagen-induced arthritis (CIA) were significantly reduced in fXIII-deficient mice. However, the most striking difference in outcome was the preservation of cartilage and bone in fXIIIA(-/-) mice concurrent with reduced osteoclast numbers and activity. The local expression of osteoclast effectors receptor activator of nuclear factor-κB ligand (RANKL) and tartrate resistant acid phosphatase were significantly diminished in CIA-challenged and even unchallenged fXIIIA(-/-) mice relative to wild-type animals, but were similar in wild-type and fibrinogen-deficient mice. Impaired osteoclast formation in fXIIIA(-/-) mice was not due to an inherent deficiency of monocyte precursors, but it was linked to reduced RANKL-driven osteoclast formation. Furthermore, treatment of mice with the pan-transglutaminase inhibitor cystamine resulted in significantly diminished CIA pathology and local markers of osteoclastogenesis. Thus, eliminating fXIIIA limits inflammatory arthritis and protects from cartilage and bone destruction in part through mechanisms linked to reduced RANKL-mediated osteoclastogenesis. In summary, therapeutic strategies targeting fXIII activity may prove beneficial in limiting arthropathies and other degenerative bone diseases.

Fibrinogen and factor XIII at the intersection of coagulation, fibrinolysis and inflammation.

Fibrinogen and factor XIII are two essential proteins that are involved directly in fibrin gel formation as the final step of a sequence of reactions triggered by a procoagulant stimulus. Haemostasis is the most obvious function of the resulting fibrin clot. Different variables affect the conversion of fibrinogen to fibrin as well as the mode of fibrin polymerisation and fibrin crosslinking, hereby, critically influencing the architecture of the resulting fibrin network and consequently determining its mechanical strength and resistance against fibrinolysis. Due to fibrinogen's structure with a multitude of domains and binding motifs the fibrin gel allows for complex interactions with other coagulation factors, with profibrinolytic as well as antifibrinolyic proteins, with complement factors and with various cellular receptors. These interactions enable the fibrin network to control its own further state (i. e. expansion or degradation), to influence innate immunity, and to function as a scaffold for cell migration processes. During the whole process of fibrin gel formation biologically active peptides and protein fragments are released that additionally influence cellular processes via chemotaxis or by modulating cell-cell interactions. Thus, it is not surprising that fibrinogen and factor XIII in addition to their haemostatic function influence innate immunity as well as cell-mediated reactions like wound healing, response to tissue injury or inflammatory processes. The present review summarises current knowledge of fibrinogen's and factor XIII's function in coagulation and fibrinolysis giving special emphasis on their relation to inflammation control.

Tissue-regenerating functions of coagulation factor XIII.

The protransglutaminase factor XIII (FXIII) has recently attracted attention within the field of tissue regeneration, as it has been found that FXIII significantly influences wound healing by exerting a multitude of functions. It supports hemostasis by enhancing platelet adhesion to damaged endothelium, and by its cross-linking activity it stabilizes the formed fibrin clot. Furthermore, FXIII limits bacterial dissemination from the wound and incorporates macromolecules of importance for cellular infiltration, supporting cell migration and survival. FXIII-mediated complex formation of the vascular endothelial growth factor receptor 2 and αV ß3 integrin is important for angiogenesis, supporting the formation of granulation tissue. Chronic inflammatory conditions involving bleeding and activation of the coagulation cascade have been shown to lead to reduced FXIII levels in plasma. Of particular importance for this review is the fact that patients suffering from inflammatory bowel disease (IBD) have reduced FXIII antigen levels and activity. Furthermore, these patients show impaired mucosal healing, which supports the inflammatory state of the disease. This review summarizes the role of FXIII in the healing of wounds, and briefly summarizes the previous use of FXIII in clinical settings. Moreover, it addresses the potential role for FXIII as a therapeutic agent in the healing of persistent wounds during chronic conditions, with an emphasis on IBD.

Biology of Factor XIII and clinical manifestations of Factor XIII deficiency.

Factor XIII (FXIII) is activated by thrombin to form a transglutaminase (FXIIIa) that stabilizes clot formation by the cross-linking of fibrin monomers and antifibrinolytic proteins. Although rare, FXIII deficiency is characterized by variable bleeding manifestations depending on the magnitude of the deficiency. A congenital FXIII deficiency with levels less than 1% can be detected in children who present with prolonged bleeding from the umbilical stump as well as protracted bleeding after trauma. An acquired FXIII deficiency may occur in a number of diseases or clinical situations where FXIII levels and/or its activity are decreased. Patients may also develop a relative deficiency in FXIII as a result of hemorrhage or dilutional changes from transfusions during surgery or trauma and are at increased risk for postoperative bleeding. Genetic studies have identified a wide range of mutations that affect the activity of the FXIII protein but in lieu of molecular genetic analyses, FXIII deficiency can be identified by specific diagnostic assays that measure either the transglutaminase activity of the protein or the levels of the protein and its individual subunits. Replacement therapy has also been shown to increase FXIII levels and reduce bleeding symptoms in patients with congenital FXIII deficiency. This review presents recent findings on the biology of FXIII and the clinical manifestations observed among patients with congenital and acquired FXIII deficiencies.

Hemorrhagic acquired factor XIII (13) deficiency and acquired hemorrhaphilia 13 revisited.

Coagulation factor XIII (F13) circulates in blood as a heterotetramer composed of an A subunit dimer and a B subunit dimer. It is activated by thrombin and crosslinks fibrin monomers. Congenital F13 deficiency demonstrates a lifelong bleeding tendency, abnormal wound healing, and recurrent miscarriages, and it first manifests as umbilical bleeding after birth. In contrast, secondary F13 deficiencies due to its overconsumption and/or hypobiosynthesis by disseminated intravascular coagulation, major surgery, liver diseases, and other disorders are rather common but rarely complicated with bleeding symptoms. Recently, consultations with physicians who have patients with hemorrhagic-acquired F13 deficiency with anti-F13 inhibitors (acquired hemorrhaphilia 13) have indicated an increase in this disease in Japan. We performed a nationwide survey, supported by the Japanese Ministry of Health, Welfare and Labor and confirmed 21 Japanese cases of this disease with anti-F13 inhibitors. Because neither prolonged clotting times nor reduced platelet counts are observed in patients with this disease, many more cases may have been overlooked. Physicians must be mindful of acquired hemorrhaphilia 13 when seeing such patients and should measure F13 activity. Products containing F13 are effective for hemostasis generally, and immunosuppressive therapy must be started immediately to eradicate anti-F13 antibodies.

F. XIII in perioperative coagulation management.

Unexplained intra-operative coagulopathies continue to be a diagnostic and therapeutic dilemma. The pathophysiology behind unexplained intra-operative coagulopathies is of great variety and complexity (pre-existing coagulopathies, dilutional coagulopathy, interactions of medications, etc.). We have shown in prospective studies that patients undergoing elective surgery who develop 'unexplained' intra-operative bleeding have significantly less F. XIII per unit thrombin available at any point in time (i.e., also already preoperatively) than patients without such coagulopathies. The consequence is a significant loss of clot firmness associated with an increase in intra-operative blood loss. Thus, these patients have less cross-linking capacity to begin with, which explains their preoperatively increased fibrin monomer concentration. It is important to note that the acquired (or compared with the amount of thrombin generated 'relative') F. XIII deficiency in situations with surgical stress shows early clinical relevance (i.e., clinical manifestation occurs even with only mild-to-moderate deficiency); this differs from the experiences with patients with congenital F. XIII deficiency, where a pronounced deficiency must be present to have clinically significant (spontaneous) bleeding. Patients undergoing elective surgery and having increased preoperative fibrin monomer concentration (as a marker of decreased cross-linking capacity) are at risk for increased intra-operative blood loss. At least one proof-of-principle landmark study suggests that such patients benefit from treatment with F. XIII early intra-operatively. This new concept helps to explain the pathophysiology behind unexplained intra-operative coagulopathies and thus allows for corresponding treatment strategies.

Factor XIII transglutaminase supports hematogenous tumor cell metastasis through a mechanism dependent on natural killer cell function.

BACKGROUND: Multiple studies suggest that the hemostatic and innate immune systems functionally cooperate in establishing the fraction of tumor cells that successfully form metastases. In particular, platelets and fibrinogen have been shown to support metastatic potential through a mechanism coupled to natural killer (NK) cell function. As the transglutaminase that ultimately stabilizes platelet/fibrin thrombi through the covalent crosslinking of fibrin, factor (F) XIII is another thrombin substrate that is likely to support hematogenous metastasis. OBJECTIVE: Directly define the role of FXIII in tumor growth, tumor stroma formation, and metastasis. METHODS: Tumor growth and metastatic potential were quantitatively and qualitatively evaluated in wild-type mice and gene-targeted mice lacking the catalytic FXIII-A subunit. RESULTS: Loss of FXIIIa function significantly diminished hematogenous metastatic potential in both experimental and spontaneous metastasis assays in immunocompetent mice. However, FXIII was not required for the growth of established tumors or tumor stroma formation. Rather, detailed analyses of the early fate of circulating tumor cells revealed that FXIII supports the early survival of micrometastases by a mechanism linked to NK cell function. CONCLUSIONS: Factor XIII is a significant determinant of metastatic potential and supports metastasis by impeding NK cell-mediated clearance of tumor cells. Given that these findings parallel previous observations in fibrinogen-deficient mice, an attractive hypothesis is that FXIII-mediated stabilization of fibrin/platelet thrombi associated with newly formed micrometastases increases the fraction of tumor cells capable of evading NK cell-mediated lysis.

A coagulation factor becomes useful in the study of acute leukemias: studies with blood coagulation factor XIII.

The intracellular form of the coagulation factor XIII has previously been identified by immunomorphological techniques using polyclonal antibodies. In these studies, only the A subunit (FXIII-A) was detectable in megakaryocytes/platelets and in monocytes/macrophages. We developed several novel monoclonal antibody clones directed to both subunits (FXIII-A and FXIII-B) and investigated their appearance in normal and leukemic cells. By using 3- and 4-color flow cytometry FXIII expression was investigated in normal peripheral blood and bone marrow samples and in acute myeloblastic (AML) and lymphoblastic (ALL) leukemia cases. Samples were studied by Western blotting and confocal laser scanning microscopy. With a previously published ELISA assay applying two monoclonal antibodies directed to different epitopes in FXIII-A, we were able to measure the intracytoplasmic content of FXIII-A in normal cells and leukemic blasts. FXIII-A was detectable in normal peripheral blood monocytes and in large quantities in platelets, but both cell types were negative for FXIII-B. There was no surface staining for FXIII-A, it only appeared intracellularly. In samples derived from patients with AML M4 and M5, FXIII-A sensitively identified blast cells. Although normal lymphocytes do not express FXIII-A, 40% of ALL cases showed significant FXIII-A expression as determined by flow cytometry. FXIII-A positivity of lymphoblasts was verified by Western blotting, ELISA, and confocal laser scanning microscopy cytometry. These data provide evidence that FXIII-A is a sufficiently sensitive marker in differentiating myeloblasts and monoblasts and is suitable for identifying leukemia-associated phenotypes in ALL.

Roles of transglutaminases in cardiac and vascular diseases.

All transglutaminases share the common enzymatic activity of transamidation, or the cross-linking of glutamine and lysine residues to form N epsilon (gamma-glutamyl) lysyl isopeptide bonds. The plasma proenzyme factor XIII is responsible for stabilizing the fibrin clot against physical and fibrinolytic disruption. Another member of the transglutaminase family, tissue transglutaminase or TG2 is abundantly expressed in cardiomyocytes, vascular cells and macrophages. The transglutaminases have a variety of functions independent of their transamidating activity. For example, TG2 binds and hydrolyzes GTP, thereby fostering signal transduction by several G protein coupled receptors. Accumulating evidence points to novel roles for factor XIII and TG2 in cardiovascular biology including: (a) modulating platelet activity, (b) regulating glucose control, (c) contributing to the development of hypertension, (d) influencing the progression of atherosclerosis, (e) regulating vascular permeability and angiogenesis (f) and contributing to myocardial signaling, contractile activity and ischemia/reperfusion injury. In this review, we summarize the cardiovascular biology of two members of the family of transglutaminases, Factor XIII and TG2.

[Fibrin monomer and factor XIII: a new concept for unexplained intraoperative coagulopathy]. / Fibrinmonomer und Faktor XIII: neues Konzept bei ungeklärter intraoperativer Blutungsneigung.

Unexplained intraoperative coagulopathies continue to be a diagnostic and therapeutic dilemma. The pathophysiology behind unexplained intraoperative coagulopathies is of great variety and complexity (preexisting coagulopathies, dilutional coagulopathy, interactions of medications etc.). We have shown in prospective studies that patients undergoing elective surgery who develop "unexplained" intraoperative coagulopathies have significantly less FXIII per unit thrombin available at any point in time (i.e. already preoperatively) than patients without such coagulopathies. The consequence is a significant loss of clot firmness associated with an increase in intraoperative blood loss. Thus, these patients have less cross-linking capacity to begin with, which explains their preoperatively increased fibrin monomer concentration. The association of increased preoperative fibrin monomer and increased intraoperative blood loss was prospectively evaluated and confirmed in a separate clinical study. It is important to note that the acquired or (compared to the amount of thrombin generated) relative F. XIII deficiency in situations with surgical stress shows early clinical relevance (even if only mild to moderate changes are present); this differs from the experiences with patients with inborn FXIII deficiency, where a pronounced deficiency must be present to have clinically significant spontaneous bleeding. Patients undergoing elective surgery, without clinically obvious coagulopathy but increased preoperative fibrin monomer concentration (as a marker of decreased crosslinking capacity) are at risk for increased intraoperative blood loss. This new concept helps to explain the pathophysiology behind unexplained intraoperative coagulopathies and thus allows for corresponding treatment strategies. Further clinical studies for early detection and interventions in patients with such coagulopathies are necessary.

Role of coagulation factor XIII (FXIII) in angiogenesis and tissue repair.

Factor FXIII (FXIII) is a plasma transglutaminase that catalyzes the cross link formation between fibrin chains to stabilize the clot. Beside it s function in hemostasis FXIII has a role in wound healing and embryo implantation--processes that involve angiogenesis. In this review we discuss the role of FXIII in angiogenesis and the molecular mechanisms underlying its pro-angiogenic effect. In addition, FXIII role in wound repair is discussed.

Flow-dependent remodeling of small arteries in mice deficient for tissue-type transglutaminase: possible compensation by macrophage-derived factor XIII.

Chronic changes in blood flow induce an adaptation of vascular caliber. Thus, arteries show inward remodeling after a reduction in blood flow. We hypothesized that this remodeling depends on the crosslinking enzyme tissue-type transglutaminase (tTG). Flow-dependent remodeling was studied in wild-type (WT) and tTG-null mice using a surgically imposed change in blood flow in small mesenteric arteries. WT mice showed inward remodeling after 2 days of low blood flow, which was absent in arteries from tTG-null mice. Yet, after continued low blood flow for 7 days, inward remodeling was similar in arteries from WT and tTG-null mice. Studying the alternative pathways of remodeling, we identified a relatively high expression of the plasma transglutaminase factor XIII in arteries of WT and tTG-null mice. In addition, vessels from both WT and tTG-null mice showed the presence of transglutaminase-specific crosslinks. An accumulation of adventitial monocytes/macrophages was found in vessels exposed to low blood flow in tTG-null mice. Because monocytes/macrophages may represent a source of factor XIII, tTG-null mice were treated with liposome-encapsulated clodronate. Elimination of monocytes/macrophages with liposome-encapsulated clodronate reduced both the expression of factor XIII and inward remodeling in tTG-null mice. In conclusion, tTG plays an important role in the inward remodeling of small arteries associated with decreased blood flow. Adventitial monocytes/macrophages are a source of factor XIII in tTG-null mice and contribute to an alternative, delayed mechanism of inward remodeling when tTG is absent.

The association between factor XIII Val34Leu polymorphism and early myocardial infarction.

BACKGROUND: Activated factor XIII (FXIII) cross-links between fibrin monomers, thus increasing the clot stability and resistance to fibrinolysis. Congenital FXIII deficiency causes severe bleeding diathesis. Recently, a common polymorphism of the FXIII A subunit (FXIII Val34Leu) has been identified as a protective factor against both arterial and venous thrombosis. The aim of this study was to investigate the role of FXIII Val34Leu polymorphism in coronary artery thrombosis, especially in young patients. METHODS AND RESULTS: One hundred and thirty patients under than 60 years of age with a history of myocardial infarction (%) and 130 healthy control subjects in the same age group were included to our study. Genomic DNA was extracted from venous blood samples and the polymerase chain reaction method was used to genotype FXIII Val34Leu polymorphism. Coronary risk factors such as obesity, diabetes mellitus, hyperlipidemia and smoking were compared between the groups with chi-square test and logistic regression analysis. The Leu allele frequency was significantly lower in patient group compared to control group (7.69% vs 19.23%, p=0.0001, chi-square). This difference was extremely significant in patients younger than 50 years-old (5.26% vs 19.64%, p<0.0001, chi-square). CONCLUSION: Our findings support the hypothesis that Val34Leu polymorphism in FXIII gene has a protective effect against myocardial infarction.

Factor XIII (FXIII) and angiogenesis.

Factor XIII is a plasma transglutaminase that participates in the final stage of the coagulation cascade. Thrombin-activated FXIII (FXIIIa) catalyzes the formation of covalent cross-links between gamma-glutamyl and epsilon-lysyl residues on adjacent fibrin chains in polymerized fibrin to yield the mature clot. In addition to its role in hemostasis, FXIII is known to participate in wound healing and embryo implantation, which are processes involving angiogenesis. In this review, we discuss the role of FXIII in angiogenesis and the molecular mechanisms underlying its proangiogenic effects. The FXIII role in tissue repair and remodeling may at least in part be attributed to its pro-angiogenic activity.

Molecular mechanisms underlying the proangiogenic effect of factor XIII.

OBJECTIVE: Coagulation Factor XIII (FXIII) was previously shown by us to induce angiogenesis. The aim of this study was to elucidate the molecular events underlying the proangiogenic effects of activated FXIII (FXIIIa) on human umbilical vein endothelial cells (HUVECs). METHODS AND RESULTS: As shown by coimmunoprecipitation studies, FXIIIa crosslinked alpha(v)beta3 with vascular endothelial growth factor receptor 2 (VEGFR-2) and enhanced the noncovalent interaction between the 2 receptors. In addition, FXIIIa induced tyrosine phosphorylation of VEGFR-2 in both the crosslinked high-molecular-weight and the noncovalent VEGFR-2/alpha(v)beta3 complexes. These effects as well as FXIIIa-induced proliferation and migration of HUVECs were abolished by iodoacetamide treatment of FXIIIa (I-FXIII) or by PTKI, an inhibitor of VEGFR-2. FXIIIa induced upregulation of c-Jun and Egr-1 as revealed by quantitative RT-PCR. Electrophoretic mobility-shift assay experiments showed that FXIIIa treatment of HUVECs enhanced binding of Wilm's tumor-1 (WT-1) but not of early growth response (Egr)-1 to the thrombospondin-1 (TSP-1) promoter sequence, suggesting that WT-1 but not Egr-1 is involved in downregulation of TSP-1 expression. CONCLUSIONS: The proangiogenic effect of FXIIIa is mediated by (1) enhancement of crosslinked and noncovalent alpha(v)beta3/VEGFR-2 complex formation; (2) tyrosine phosphorylation and activation of VEGFR-2; (3) upregulation of c-Jun and Egr-1; and (4) downregulation of TSP-1 induced indirectly by c-Jun through WT-1. These processes may clarify FXIII role in vascular remodeling and tissue repair.

Possible role of factor XIII subunit A in Fcgamma and complement receptor-mediated phagocytosis.

Besides its traditional role in hemostasis, factor XIII subunit A (FXIII-A) is supposed to function as a cellular transglutaminase and to be involved in certain intracellular processes, including cytoskeletal remodeling. To investigate its intracellular role, the aim of the present study was to follow changes in FXIII-A production in combination with the receptor-mediated phagocytic activities of monocytes/macrophages and to examine the phagocytic functions of monocytes in patients with FXIII-A deficiency. Human blood monocytes were isolated from the buffy coats of healthy volunteers and cultured for 4 days. The FcgammaR-mediated phagocytosis of sensitized erythrocytes (EA) and the complement receptor (CR)-mediated phagocytosis of complement-coated yeast particles were studied during monocyte/macrophage differentiation. Changes in the gene expression of FXIII-A were detected by real-time quantitative RT-PCR. FXIII-A protein production was investigated with fluorescent image analysis at single cell level and Western immunoblot analysis. Both the FcgammaR and CR-mediated phagocytosis increased during culturing, which peaked on day 3. The phagocytic activity of the cells could be markedly inhibited with monodansylcadaverine, an inhibitor of the transglutaminase-induced crosslinking of proteins. The phagocytosis of EA, complement-coated and uncoated yeast particles was found to be strongly diminished in monocytes of FXIII-A deficient patients. The phagocytic functions of cultured cells showed a change in parallel with the alterations in FXIII-A mRNA expression, as well as with that in FXIII-A in protein synthesis detected by image and Western immunoblot analyses in concert. Our results suggest that FXIII-A plays a role in the Fcgamma and complement receptor-mediated phagocytic activities of monocytes/macrophages.