Interaction between Antiphospholipid Antibodies and Protein C Anticoagulant Pathway: A Narrative Review

2022 ◽  
Author(s):  
Vittorio Pengo
Keyword(s):  
Antiphospholipid Antibodies ◽  
Protein C ◽  
Activated Protein C ◽  
Severe Form ◽  
Protein C Deficiency ◽  
Small Vessels ◽  
Gray Area ◽  
Glycoprotein I

AbstractThrombotic antiphospholipid syndrome (APS) is a condition in which thrombosis in venous, arterial, and/or small vessels is ascribed to the presence of antiphospholipid antibodies (aPL). Among the various proposed pathogenic theories to explain thrombotic APS, those involving the interaction between aPL and the protein C system have gained much consensus. Indeed, robust data show an acquired activated protein C resistance (APC-R) in these patients. The role of aPL in this impairment is clear, but the mechanism of action is uncertain, as the type of aPL and to what extent aPL are involved remains a gray area. Lupus anticoagulant (LA) is often associated with APC-R, but antibodies generating LA comprise those directed to β2-glycoprotein I and antiphosphatidylserine/prothrombin. Moreover, the induction of APC-R by aPL requires the presence of phospholipids and is suppressed by the presence of an excess of phospholipids. How phospholipids exposed on the cell membranes work in the system in vivo is unknown. Interestingly, acquired APC-R due to aPL might explain the clinical phenotypes of thrombotic APS. Indeed, the literature reports cases of both venous and arterial thromboembolism as well as skin necrosis, the latter observed in the severe form of protein C deficiency and in catastrophic APS.

Release of High Levels of Platelet Factor 4 (PF4) from Platelets Improves Survival after a Lethal Lipopolysaccharide (LPS) Challenge.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 61-61
Author(s):  
M. Anna Kowalska ◽  
Michele P. Lambert ◽  
Lubica Rauova ◽  
William J. Smith ◽  
Shawn A. Mahmud ◽  
...  
Keyword(s):  
Protein C ◽  
Activated Protein C ◽  
Physiological Role ◽  
Protein C Deficiency ◽  
Platelet Factor ◽  
Lps Challenge ◽  
Inflammatory State ◽  
Platelet Infusion

Abstract Infusion of activated protein C (APC) improves survival in sepsis. PF4 is a CXC chemokine predominantly expressed during megakaryopoiesis and stored in platelet alpha-granules whose biological function(s) are not well understood. We have shown that recombinant PF4 enhances APC generation by thrombin/thrombomodulin complexes both in vitro and in vivo. Would endogenous PF4 released from platelets activated during an inflammatory state similarly affect APC production? We addressed this issue using mice that were either completely devoid of PF4 (mPF4−/−) or had a 6-fold excess of human PF4 (hPF4+). Using a lethal LPS challenge model (O111:B4, 40 mg/kg IP), we examined whether platelets become activated and release PF4 during endotoxemia. Two hours after LPS injection, the platelet count in mice decreased to ~70% of baseline levels (p=0.006). Serum PF4, as measured by ELISA, also dropped to ~60% of baseline from 47±5 kU/ml to 30±5 kU/ml (p=0.002). At the same time, plasma PF4 level was increased by 20%, consistent with LPS resulting in PF4 release. The smaller increase than expected suggests that much of the released PF4 binds immediately to the surface of vascular cells. Consistent with this, we have observed higher accumulation of PF4 in mouse lungs after LPS injection compared to uninjected mice (990±220 and 660±120 U/mg, respectively, p=0.017). APC generation was assessed 10 min after thrombin infusion (80 U/kg. IV) as a measure of endogenous platelet PF4’s effect in an inflammatory/procoagulant state. In mPF4−/− mice APC levels were 72% of that in wild type (WT) mice (p=0.0006) while in hPF4+ mice APC formation increased to 178% (p=0.003). Survival of mice 24 hrs after LPS (25 mg/kg) challenge was then examined. hPF4+ mice had a mortality rate of 9% compared to ~40% in both WT and mPF4−/− (p< 0.001). To examine the role of APC in this improved survival, we performed similar experiments with mice heterozygous for protein C deficiency (PC+/−). More PC+/− mice died 16 hrs after injection of 40 mg/kg LPS than WT mice (61% vs. 29% mortality respectively, p=0.005), while mortality for hPF4+/PC+/− mice was significantly lower (14%, p< 0.001 compared to PC+/− mice), supporting the hypothesis that the protective effect of PF4 is at least in part due to increased APC generation. Next we asked if infusion of platelets with high PF4 is protective in the LPS model. We injected either vehicle buffer or mPF4−/− or hPF4+ platelets (3×108 per 20 g mouse) into WT mice prior to treatment with LPS. Mortality of mice at 24 hrs after LPS injection with mPF4−/−platelet infusion was not significantly different than mice with buffer infusion (86% vs. 96% respectively, p=0.4), but mortality was significantly lower when hPF4+ platelets were infused (58% vs. 96%, p=0.01). Our results suggest that PF4 is released from platelets after an inflammatory stimulus and that this may have a positive physiological role by enhancing APC generation. High endogenous platelet PF4 levels may have a survival advantage after exposure to endotoxins. Infusion of platelets containing high levels of PF4 in sepsis may be a novel therapeutic strategy that warrants further investigation.

Antiphospholipid Antibodies with LAC Activity That Bind beta2-Glycoprotein I Cause Increased Resistance Against Activated Protein C.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3622-3622
Author(s):  
Bas de Laat ◽  
Sander B. Meijer ◽  
Carel M. Eckmann ◽  
M. van Schagen ◽  
Koen Mertens ◽  
...  
Keyword(s):  
Antiphospholipid Antibodies ◽  
Protein C ◽  
Activated Protein C ◽  
Plasma Samples ◽  
Surface Plasmon Resonance Analysis ◽  
Resonance Analysis ◽  
Igm Antibodies ◽  
Apc Resistance ◽  
Glycoprotein I ◽  
Direct Binding

Abstract Background: The antiphospholipid syndrome is characterized by the occurrence of vascular thrombosis combined with the presence of antiphospholipid antibodies (aPL) in plasma of patients. Recently it was published that aPL with lupus anticoagulant activity (LAC), caused by anti-beta2-glycoprotein I (beta2GPI) antibodies, highly correlate with a history of thrombosis. aPL-related resistance against activated protein C (APC) is one of the proposed mechanism responsible for thrombosis. We investigated a possible correlation between a beta2GPI-dependent LAC and increased APC-resistance in a population of 22 plasma samples with LAC activity. Methods: Twenty-two LAC-positive plasma samples were tested for beta2GPI-dependence (titration of cardiolipin into an APTT-based assay), increased APC-resistance, anti-beta2GPI IgG/IgM antibodies, anti-prothrombin IgG/IgM antibodies and anti-protein C IgG/IgM antibodies. In addition, a monoclonal anti-beta2GPI antibody and patient-purified IgG (both with LAC activity) were diluted in plasma with/without protein C and tested for occurrence of a beta2GPI-dependent LAC (normalization of clotting time by the addition of cardiolipin). To study aPL-induced APC-resistance in more detail, surface plasmon resonance analysis was used to investigate binding between APC and beta2GPI in the presence/absence of a mouse-derived monoclonal anti-beta2GPI antibody. Results: Eleven plasma samples that displayed a beta2GPI-dependent LAC also showed increased APC resistance. In contrast, only 1 of the 11 plasma samples with a beta2GPI-independent LAC displayed increased APC-resistance. None of the other serological parameters (antibodies against beta2-glycoprotein I, prothrombin or protein C) displayed the same association with increased APC resistance as a beta2-glycoprotein I dependent LAC. Furthermore, we found a linear correlation between the potency of a beta2GPI-dependent LAC and the level of APC-resistance. When a monoclonal anti-beta2GPI antibody and a patient-purified IgG were tested for a beta2GPI-dependent LAC, both antibodies did not display a beta2GPI-dependent LAC when diluted in protein C deficient plasma. In literature it has been proposed that direct binding of beta2GPI to APC results in a decreased activity of APC. By using surface plasmon resonance analysis, we found that beta2GPI displayed a higher affinity for coated APC in the presence of the monoclonal anti-beta2GPI antibody (4 nM) compared to beta2GPI alone (400 nM). Conclusion: The results of this study indicate that by adding cardiolipin into an APTT-based clotting assay, one can detect beta2GPI-dependent LAC based on increased resistance against APC. Increased resistance against activated protein C might result from direct binding of beta2GPI to activated protein C. In conclusion, our observations indicate a direct correlation between a major clinical symptom of APS (thrombosis), a diagnostic assay (beta2GPI-dependent LAC) and a potential mechanism responsible for thrombosis in the antiphospholipid syndrome (increased APC-resistance).

scholarly journals Coagulation and fibrinolytic activities in 2 siblings with β2-glycoprotein I deficiency

Blood ◽  
2000 ◽  
Vol 96 (4) ◽  
pp. 1594-1595
Author(s):  
Rie Takeuchi ◽  
Tatsuya Atsumi ◽  
Masahiro Ieko ◽  
Hiroyuki Takeya ◽  
Shinsuke Yasuda ◽  
...  
Keyword(s):  
Protein C ◽  
Thrombin Generation ◽  
Anticoagulant Activity ◽  
Activated Protein C ◽  
Healthy Woman ◽  
Contact Activation ◽  
Glycoprotein I ◽  
Normal Ranges

β2-Glycoprotein I (β2GPI) is a major antigen for antiphospholipid antibodies, and its multiple in vitro functions have been reported. This glycoprotein not only down-regulates thrombin formation by inhibiting contact activation or prothrombinase activity, but also up-regulates coagulation by reducing protein C anticoagulant activity. However, the in vivo roles of β2GPI remain obscure. Coagulation and fibrinolytic characteristics were investigated in individuals with β2GPI deficiency. An apparently healthy woman and her brother are homozygotes for β2GPI deficiency. In these patients, Russell viper venom time was shortened (40.4 seconds; normal range, 47.8 ± 4.95 seconds), but all markers of thrombin generation and fibrin turnover were within normal ranges. Exogenous activated protein C adequately prolonged the clotting time of the β2GPI-deficient plasma, and euglobulin lysis time was also normal. Thus, elevated thrombin generation, enhancement of activated protein C response, and an altered fibrinolytic system were not found in congenitally β2GPI-deficient plasma.

Paediatric thrombo-embolism: the influence of non-genetic factors and the role of activated protein C resistance and protein C deficiency

1997 ◽  
Vol 156 (4) ◽  
pp. 277-281 ◽  
Author(s):  
M. M. Uttenreuther-Fischer ◽  
B. Vetter ◽  
C. Hellmann ◽  
U. Otting ◽  
S. Ziemer ◽  
...  
Keyword(s):  
Protein C ◽  
Genetic Factors ◽  
Activated Protein C ◽  
Activated Protein C Resistance ◽  
Protein C Deficiency

Platelet-Endothelial Interactions: Sepsis, HIT, and Antiphospholipid Syndrome

Hematology ◽  
2003 ◽  
Vol 2003 (1) ◽  
pp. 497-519 ◽  
Author(s):  
Theodore E. Warkentin ◽  
William C. Aird ◽  
Jacob H. Rand
Keyword(s):  
Antiphospholipid Syndrome ◽  
Protein C ◽  
Clinical Laboratory ◽  
Activated Protein C ◽  
Platelet Factor ◽  
Glycoprotein I ◽  
Acquired Abnormalities ◽  
Risk For Thrombosis ◽  
Condition Diagnosis

Abstract Acquired abnormalities in platelets, endothelium, and their interaction occur in sepsis, immune heparin-induced thrombocytopenia (HIT), and the antiphospholipid syndrome. Although of distinct pathogeneses, these three disorders have several clinical features in common, including thrombocytopenia and the potential for life- and limb-threatening thrombotic events, ranging from microvascular (sepsis > antiphospholipid > HIT) to macrovascular (HIT > antiphospholipid > sepsis) thrombosis, both venous and arterial. In Section I, Dr. William Aird reviews basic aspects of endothelial-platelet interactions as a springboard to considering the common problem of thrombocytopenia (and its mechanism) in sepsis. The relationship between thrombocytopenia and other aspects of the host response in sepsis, including activation of coagulation/inflammation pathways and the development of organ dysfunction, is discussed. Practical issues of platelet count triggers and targeted use of activated protein C concentrates are reviewed. In Section II, Dr. Theodore Warkentin describes HIT as a clinicopathologic syndrome, i.e., the diagnosis should be based on the concurrence of an appropriate clinical picture together with detection of platelet-activating and/or platelet factor 4-dependent antibodies (usually in high levels). HIT is a profound prothrombotic state (odds ratio for thrombosis, 20–40), and the risk for thrombosis persists for a time even when heparin is stopped. Thus, pharmacologic control of thrombin (or its generation), and postponing oral anticoagulation pending substantial resolution of thrombocytopenia, is appropriate. Indeed, coumarin-associated protein C depletion during uncontrolled thrombin generation of HIT can explain limb loss (coumarin-associated venous limb gangrene) or skin necrosis syndromes in some patients. In Section III, Dr. Jacob Rand presents the most recent concepts on the mechanisms of thrombosis in the antiphospholipid syndrome, and focuses on the role of β2-glycoprotein I as a major antigenic target in this condition. Diagnosis of the syndrome is often complicated because the clinical laboratory tests to identify this condition have been empirically derived. Dr. Rand addresses the practical aspects of current testing for the syndrome and current recommendations for treating patients with thrombosis and with spontaneous pregnancy losses.

scholarly journals In Vivo hemostatic Significance of Activated Protein C in Factor VIIIa Regulation

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 93-93
Author(s):  
Amelia R. Wilhelm ◽  
Nicole A. Parsons ◽  
Charles T. Esmon ◽  
Rodney M. Camire ◽  
Lindsey A. George
Keyword(s):  
Blood Loss ◽  
Protein C ◽  
Activated Protein C ◽  
Enzyme Complex ◽  
Hemostatic Effect ◽  
Safety Considerations ◽  
A2 Domain ◽  
Tail Clip

Activated factor VIII (FVIIIa) is an essential cofactor in the intrinsic tenase (Xase) enzyme complex that generates factor Xa and propagates clot formation. The FVIIIa heterotrimer is comprised of a metal ion linked dimer (A1/A3-C1-C2 domains) that is associated with the A2 domain by weak non-covalent interactions. Regulation of FXa formation by the intrinsic Xase enzyme complex occurs by FIXa inhibition and mechanisms contributing to FVIIIa inactivation, including: 1) rapid A2 domain dissociation and 2) activated protein C (APC) cleavage of FVIIIa. While FVIIIa inactivation by APC is considered important, there are surprisingly no in vivo studies documenting the hemostatic role of APC in FVIIIa regulation. Further, published data demonstrate APC cleavage of FVIIIa at physiologic protein concentrations occurs over hours while A2 dissociation occurs rapidly over minutes. Thus, it is thought that the predominant mechanism of FVIIIa inactivation is A2 dissociation and APC likely plays a marginal role in FVIIIa regulation. Additionally, unlike described A2 mutations that enhance dissociation and cause hemophilia A (HA), there is no known disease state attributed to altered FVIIIa cleavage by APC. This is in contrast to FVIII's homologous protein, FVa, whereby resistance to APC cleavage is the most common inherited thrombophilia (FV-Leiden [FVL]). Understanding the physiologically relevant mechanisms of FVIIIa inactivation has immediate clinical applicability for understanding safety considerations in HA therapeutics that bypass FVIIIa regulation (FVIII mimetic antibodies, e.g. emicizumab). Further, as evidenced by successful hemophilia B gene therapy trials using a gain of function FIX variant (FIX-Padua), altering FVIIIa inactivation could be exploited for therapeutic benefit in the setting of gene transfer. We aimed to determine the in vivo hemostatic role of APC in FVIIIa regulation and pair these studies with purified system analysis. We introduced Arg to Gln mutations at FVIII APC cleavage sites (R336Q and R562Q, herein called FVIII-QQ) on a B-domain deleted FVIII (FVIII-WT) backbone and produced recombinant FVIII-QQ and FVIII-WT. Unlike FVIII-WT, western blot analysis of FVIII-QQ incubated with APC and phospholipids had no evidence of cleavage. Enzyme kinetic studies using purified components demonstrated no appreciable difference in the Km or Vmax for FX within the intrinsic Xase enzyme complex or A2 dissociation of FVIII-QQ relative to FVIII-WT. These data confirmed no unexpected differences in FVIII-QQ relative to FVIII-WT. To begin to evaluate the role of APC in FVIIIa regulation, we measured thrombin generation in murine and human HA plasma reconstituted with FVIII-QQ or FVIII-WT in the presence of increasing APC concentrations. The IC50 of APC was 2-3-fold higher for FVIII-QQ than FVIII-WT. To evaluate the in vivo hemostatic effect of APC in FVIIIa regulation, HA mice were infused with FVIII-QQ or FVIII-WT and evaluated by tail clip injury and 7.5% FeCl3 carotid artery occlusion models. Required doses of FVIII-QQ to normalize blood loss from a tail clip assay and time to vessel occlusion in a FeCl3 assay were 4-5 fold lower than necessary FVIII-WT doses; the superior hemostatic effect of FVIII-QQ supported the physiologic significance of APC in FVIIIa inactivation. To isolate the role of APC in FVIIIa regulation from APC inactivation of FVa, we backcrossed HA mice with FVL mice to create homozygous HA/FVL mice. HA/FVL mice were infused with FVIII-QQ or FVIII-WT and underwent tail clip assay analysis. Doses of FVIII-QQ required to normalize blood loss were again less than FVIII-WT. To further isolate the enhanced hemostatic effect of FVIII-QQ to APC resistance, we performed the tail clip assay in HA/FVL mice infused with FVIII-QQ or FVIII-WT in the presence or absence of MPC1609, an antibody that blocks murine APC function (Xu et al. J Thromb Haemost 2008). In the presence of MPC1609, the same dose of FVIII-WT and FVIII-QQ was required to normalize blood loss (Figure 1). Collectively, our in vitro and in vivo data support the physiologic significance of APC in FVIIIa regulation. To our knowledge these data are the first to demonstrate the in vivo hemostatic effect of APC in FVIIIa inactivation. Our data may be translated to rationally exploit APC regulation of FVIIIa to develop novel HA therapeutics or further delineate safety considerations in therapies that bypass FVIIIa regulation. Figure 1 Disclosures Camire: Pfizer: Research Funding. George:University of Pennyslvania: Employment; Pfizer: Consultancy; Avrobio: Membership on an entity's Board of Directors or advisory committees.

Non β2-Glycoprotein I Cofactors for Antiphospholipid Antibodies

Lupus ◽  
1996 ◽  
Vol 5 (5) ◽  
pp. 388-392 ◽  
Author(s):  
M Galli
Keyword(s):  
Antiphospholipid Syndrome ◽  
Antiphospholipid Antibodies ◽  
Protein C ◽  
Activated Protein C ◽  
Clinical Manifestations ◽  
Annexin V ◽  
Protein S ◽  
Thromboembolic Events ◽  
Glycoprotein I ◽  
Recurrent Abortions

The Antiphospholipid Syndrome is defined by the association between peculiar clinical manifestations, namely arterial and/or venous thrombosis, recurrent abortions and thrombocytopenia, and the antiphospholipid antibodies. These antibodies are directed to plasma proteins bound to anionic phospholipids or other anionic surfaces: so far, β2-glycoprotein I is the best known and characterized antiphospholipid ‘cofactor’ ( this issue is specifically treated in other parts of this journal). In recent years, such a role has been reported also for prothrombin, activated Protein C, Protein S, Annexin V, Thrombomodulin, high- and low-molecular weight kininogens. Anti-prothrombin antibodies are detected in approximately 50% of the antiphospholipid-positive patients; conversely, limited data are available regarding the prevalence the other antibodies. ‘Cofactors' are necessary for the expression of both the immunological and the functional properties of their respective antiphospholipid antibodies. In particular, the recognition of the calcium-mediated prothrombin/lipid complex by anti-prothrombin antibodies hampers prothrombin activation, thus causing the prolongation of the phospholipid-dependent coagulation reactions. The interaction between antiphospholipid antibodies and natural inhibitors of coagulation such as activated Protein C, its non-enzymatic accessory protein Protein S or Thrombomodulin might increase the risk to develop thromboembolic events. Similarly, the presence of antibodies to surface-bound Annexin V has been hypothesized to play a role in recurrent abortions and fetal deaths. However, to clearly establish whether and which antiphospholipid antibodies represent risk factors for the thromboembolic events of the antiphospholipid syndrome, further studies of their behaviour and properties as well as the identification and characterization of (possibly) other antibodies are required.

scholarly journals Coagulation and fibrinolytic activities in 2 siblings with β2-glycoprotein I deficiency

Blood ◽  
2000 ◽  
Vol 96 (4) ◽  
pp. 1594-1595 ◽  
Author(s):  
Rie Takeuchi ◽  
Tatsuya Atsumi ◽  
Masahiro Ieko ◽  
Hiroyuki Takeya ◽  
Shinsuke Yasuda ◽  
...  
Keyword(s):  
Protein C ◽  
Thrombin Generation ◽  
Anticoagulant Activity ◽  
Activated Protein C ◽  
Healthy Woman ◽  
Contact Activation ◽  
Glycoprotein I ◽  
Normal Ranges

Abstract β2-Glycoprotein I (β2GPI) is a major antigen for antiphospholipid antibodies, and its multiple in vitro functions have been reported. This glycoprotein not only down-regulates thrombin formation by inhibiting contact activation or prothrombinase activity, but also up-regulates coagulation by reducing protein C anticoagulant activity. However, the in vivo roles of β2GPI remain obscure. Coagulation and fibrinolytic characteristics were investigated in individuals with β2GPI deficiency. An apparently healthy woman and her brother are homozygotes for β2GPI deficiency. In these patients, Russell viper venom time was shortened (40.4 seconds; normal range, 47.8 ± 4.95 seconds), but all markers of thrombin generation and fibrin turnover were within normal ranges. Exogenous activated protein C adequately prolonged the clotting time of the β2GPI-deficient plasma, and euglobulin lysis time was also normal. Thus, elevated thrombin generation, enhancement of activated protein C response, and an altered fibrinolytic system were not found in congenitally β2GPI-deficient plasma.

scholarly journals Normalization of markers of coagulation activation with a purified protein C concentrate in adults with homozygous protein C deficiency

Blood ◽  
1993 ◽  
Vol 82 (4) ◽  
pp. 1159-1164 ◽  
Author(s):  
J Conard ◽  
KA Bauer ◽  
A Gruber ◽  
JH Griffin ◽  
HP Schwarz ◽  
...  
Keyword(s):  
Protein C ◽  
Activated Protein C ◽  
Purpura Fulminans ◽  
Coagulation Activation ◽  
Protein C Deficiency ◽  
Protein C Concentrate ◽  
System Activation ◽  
Heterozygous Protein C Deficiency ◽  
Sustained Increase

Homozygous or double heterozygous protein-C deficiency can present at birth with purpura fulminans or later in life with venous thrombosis. Two homozygous patients who had previously sustained thrombotic episodes were investigated at a time when they were asymptomatic and not receiving antithrombotic therapy. The plasma levels of protein-C antigen and activity in both individuals were approximately 20% of normal. We administered a highly purified plasma-derived protein C concentrate to these individuals and monitored levels of several markers of in vivo coagulation activation. Assays for protein-C activation (activated protein C and protein C activation peptide) showed a sustained increase from reduced baseline levels, whereas thrombin generation (as measured by prothrombin fragment F1 + 2) gradually decreased over about 24 hours into the normal range. These investigations provide direct evidence that protein C is converted to activated protein C in vivo, and that the protein-C anticoagulant pathway is a tonically active mechanism in the regulation of hemostatic system activation in humans.

Thrombomodulin mutant mice with a strongly reduced capacity to generate activated protein C have an unaltered pulmonary immune response to respiratory pathogens and lipopolysaccharide

Blood ◽  
2004 ◽  
Vol 103 (5) ◽  
pp. 1702-1709 ◽  
Author(s):  
Anita W. Rijneveld ◽  
Sebastiaan Weijer ◽  
Sandrine Florquin ◽  
Charles T. Esmon ◽  
Joost C. M. Meijers ◽  
...  
Keyword(s):  
Immune Response ◽  
Protein C ◽  
Activated Protein C ◽  
Protein S ◽  
Lavage Fluid ◽  
Respiratory Pathogens ◽  
Pulmonary Response ◽  
Inflammatory Infiltrates

AbstractThe thrombomodulin–protein C–protein S (TM-PC-PS) pathway exerts anticoagulant and anti-inflammatory effects. We investigated the role of TM in the pulmonary immune response in vivo by the use of mice with a mutation in the TM gene (TMpro/pro) that was earlier found to result in a minimal capacity for activated PC (APC) generation in the circulation. We here demonstrate that TMpro/pro mice also display a strongly reduced capacity to produce APC in the alveolar compartment upon intrapulmonary delivery of PC and thrombin. We monitored procoagulant and inflammatory changes in the lung during Gram-positive (Streptococcus pneumoniae) and Gram-negative (Klebsiella pneumoniae) pneumonia and after local administration of lipopolysaccharide (LPS). Bacterial pneumonia was associated with fibrin(ogen) depositions in the lung that colocalized with inflammatory infiltrates. LPS also induced a rise in thrombin-antithrombin complexes in bronchoalveolar lavage fluid. These pulmonary procoagulant responses were unaltered in TMpro/pro mice, except for enhanced fibrin(ogen) deposition during pneumococcal pneumonia. In addition, TMpro/pro mice displayed unchanged antibacterial defense, neutrophil recruitment, and cytokine/chemokine levels. These data suggest that the capacity of TM to generate APC does not play a role of importance in the pulmonary response to respiratory pathogens or LPS.

Sign in / Sign up

Export Citation Format

Share Document