PREKALLIKREIN DEFICIENCY IN MAN

Blood plasma obtained from an individual with abnormal thromboplastin formation, due to deficiency of Fletcher factor, was fully corrected by 2% of normal, Hageman factor- or PTA-deficient plasma. It was also reconstituted by addition of highly purified human or rabbit prekallikrein. The plasma failed to generate kinin upon exposure to kaolin, a defect which was also corrected by addition of prekallikrein. Prekallikrein antigen was not detectable in this plasma. Fletcher factor-deficient plasma did not support the normal generation of PF/dil when dilute plasma was incubated in glass vessels and injected intracutaneously. Small quantities of Fletcher factor-deficient or Hageman factor-deficient plasma corrected the ability of the other to generate PF/dil. The formation of plasmin in dilute, acidified plasma incubated with kaolin was also abnormal in Fletcher factor-deficient plasma. Plasmin generation was normalized by addition of prekallikrein or small quantities of Hageman factor-deficient plasma. The data support the identity of Fletcher factor and prekallikrein.     

Williams trait. Human kininogen deficiency with diminished levels of plasminogen proactivator and prekallikrein associated with abnormalities of the Hageman factor-dependent pathways.

An asymptomatic woman (Ms. Williams) was found to have a severe abnormality in the surface-activated intrinsic coagulation, fibrinolytic, and kinin-generating pathways. Assays for known coagulation factors were nromal while Fletcher factor (pre-kallikrein) was 45%, insufficient to account for the observed markedly prolonged partial thromboplastin time. Plasminogen proactivator was present at 20% of normal levels and addition of highly purified plasminogen proactivator containing 10% plasminogen activator partially corrected the coagulation and fibrinolytic abnormalities but not the kinin-generating defect. This effect was due to its plasminogen activator content. In addition, Williams trait plasma failed to convert prekallilrein to lakkilrein or release kinin upon incubation with kaolin. Kininogen antigen was undetectable. When normal plasma was fractionated to identify the factor that corrects all the abnormalities in Williams trait plasma, the Williams factor was identified as a form of kininogen by its behavior on ion exchange chromatography, gel filtration, disc gel electrophoresis, and elution from an anti-low molecular weight kininogen immunoadsorbent. High molecular weight kininogen as well as a subfraction of low molecular weight kininogen, possessed this corrective activity while the bulk of low molecular weight kininogen functioned only as a kallikrein substrate. Kininogen therefore is a critical factor required for the functioning of Hageman factor-dependent coagulation and fibrinolysis and for the activation of prekallikrein.     

Potentiation of the function of Hageman factor fragments by high molecular weight kininogen.

Patients lacking high molecular weight (HMW) kininogen have profound abnormalities of the Hageman factor-dependent pathways of coagulation, kinin formation, and fibrinolysis. The ability of HMW kininogen to potentiate the Hageman factor fragments (HFf) activation of prekallikrein and Factor XI in plasma was studied. HFf only partially converted Factor XI to XIa and prekallikrein to kallikrein in plasma deficient in HMW kininogen (Williams trait), while enhanced activation of Factor XI and prekallikrein by HFf resulted after reconstitution with HMW kininogen. In a system using highly purified components, HMW kininogen increased the initial rate of prekallikrein activation whether the kallikrein formed was assayed by arginine esterase activity or kininforming ability. The potentiation of prekallikrein activation occurred over a 12-fold range of enzyme (HFf) concentration and was nonhyperbolic with respect to substrate (prekallikrein). HMW kininogen exerted its effect even in the absence of prekallikrein since the hydrolysis of acetylglycyl-lysine methyl ester by HFf was increased by HMW kininogen. These results suggest that one of the functions of HMW kininogen is to augment the catalytic action of HFf.     

Activation of Hageman factor (factor XII) by bismuth subgallate, a hemostatic agent

Bismuth subgallate is an effective agent in preventing hemorrhage after adenotonsillectomy. The experiments described demonstrate that this may occur through the activation of Hageman factor by this agent. Bismuth subgallate shortened the clotting time of whole blood, an action localized to an effect on the early steps of the intrinsic pathway; bismuth subgallate did not accelerate the thrombin time or prothrombin time of normal plasma, but could be substituted for kaolin as an activator of coagulation in assays of the partial thromboplastin time. The action of bismuth subgallate was localized to an effect on Hageman factor. It did not induce coagulation of plasma samples deficient in any of the recognized factors participating in the intrinsic pathway of thrombin formation, but it shortened the clotting time of plasma deficient in factor VII, a component of the extrinsic pathway. Evidence was obtained that Hageman factor exposed to bismuth subgallate corrected the defect of Hageman factor-deficient plasma and acquired amidolytic properties in the absence of other clotting factors. These studies provide a rationale for the hemostatic properties of bismuth subgallate.     

Fitzgerald Trait: Deficiency of a Hitherto Unrecognized Agent, Fitzgerald Factor, Participating in Surface-Mediated Reactions of Clotting, Fibrinolysis, Generation of Kinins, and the Property of Diluted Plasma Enhancing Vascular Permeability (PF/Dil)

The prolonged partial thromboplastin time observed in the plasma of a 71-yr-old asymptomatic man was related to the deficiency of a hitherto unrecognized agent. The patient's plasma also exhibited impaired surface-mediated fibrinolysis and esterolytic activity and impaired generation of kinins and of the property enhancing vascular permeability designated PF/Dil. The patient's plasma contained normal amounts of all known clotting factors except Fletcher factor (a plasma prekallikrein) which was present at a concentration of 10-15% of pooled normal plasma. Fletcher trait plasma, however, contained normal amounts of the agent missing from the patient's plasma and corrected the defects in clotting, fibrinolysis, and vascular permeability. Fletcher trait plasma was less effective in correcting generation of kinins and esterolytic activity, presumably because of the patient's partial deficiency of prekallikrein. The site of action of the factor deficient in the patient's plasma appeared to be subsequent to the activation of Hageman factor and plasma prekallikrein. A fraction of normal plasma, devoid of other clotting factors, corrected the defect in clotting in the patient's plasma; a similar fraction of the patient's plasma did not correct this abnormality. No evidence yet exists pointing to the familial nature of the patient's defect. Tentatively, the patient's disorder may be referred to by his surname as Fitzgerald trait, and the agent apparently deficient in his plasma as Fitzgerald factor.     

The Fibrinolytic Pathway of Human Plasma II. THE GENERATION OF CHEMOTACTIC ACTIVITY BY ACTIVATION OF PLASMINOGEN PROACTIVATOR

The conversion of plasminogen proactivator to plasminogen activator by Hageman factor fragments results in the generation of chemotactic activity for human neutrophils. This chemotactic activity can be distinguished from that generated by Hageman factor activation of prekallikrein and is demonstrable in plasma that is genetically deficient in prekallikrein (Fletcher factor deficiency). Both the plasminogen-activating activity and chemotactic activity produced by the interaction of Hageman factor fragments and plasminogen proactivator to yield plasminogen activator were inhibited by diisopropyl fluorophosphate (DFP) indicating an essential role for the enzymatic site in both these activities. The finding that the plasminogen proactivator tolerated a dose of DFP, which completely inactivated the plasminogen activator, reveals that the active site is protected in the precursor protein.     

A PREALBUMIN ACTIVATOR OF PREKALLIKREIN : III. APPEARANCE OF CHEMOTACTIC ACTIVITY FOR HUMAN NEUTROPHILS BY THE CONVERSION OF HUMAN PREKALLIKREIN TO KALLIKREIN

Human plasma kallikrein has been shown to directly and selectively attract human neutrophils from a mixed leukocyte population. The capacity of plasma kallikrein to be chemotactic and to generate the nonapeptide bradykinin was maintained during progressive purification. While neither highly purified prekallikrein nor the prealbumin Hageman factor fragments were chemotactic alone, their interaction so as to convert prekallikrein to kallikrein yielded both chemotactic and kinin-generating activity. Both functions of kallikrein were inhibited by treatment with diisopropyl fluorophosphate, indicating an essential role for the active site of the enzyme in the expression of its chemotactic activity.     

Activation and function of human Hageman factor. The role of high molecular weight kininogen and prekallikrein.

The activation and function of surface-bound Hageman factor in human plasma are dependent upon both high molecular weight (HMW) kininogen and prekallikrein. HMW kininogen does not affect the binding of Hageman factor to surfaces, but it enhances the function of surface-bound Hageman factor as assessed by its ability to activate prekallikrein and Factor XI. The initial conversion of prekallikrein to kallikrein by the surface-bound Hageman factor in the presence of HMW kininogen is followed by a rapid enzymatic activation of Hageman factor by kallikrein. The latter interaction is also facilitated by HMW kininogen. Kallikrein therefore functions as an activator of Hageman factor by a positive feedback mechanism and generates most of the activated Hageman factor during brief exposure of plasma to activating surfaces. HMW kininogen is a cofactor in the enzymatic activation of Hageman factor by kallikrein and it also augments the function of the activated Hageman factor generated. The stoichiometry of the Hagman factor interaction with HMW kininogen suggests that it enhances the activity of the active site of Hageman factor. Since HMW kininogen and prekallikrein circulate as a complex, HMW kininogen may also place the prekallikrein in an optimal position for its reciprocal interaction with Hageman factor to proceed. The surface appears to play a passive role upon which bound Hageman factor and the prekallikrein-HMW kininogen complex can interact.     

Deficiency of factor XII-dependent plasminogen proactivator in prekallikrein-deficient plasma.

Normal human plasma contains a factor XII (Hageman factor)-dependent plasminogen proactivator in its gamma globulin fraction. On the basis of both fibrin plate and clot lysis assays, this plasminogen proactivator activity was shown to be absent from the gamma globulin fraction of prekallikrein (Fletcher factor)-deficient plasma of two unrelated patients. This observation suggests that factor XII-dependent plasminogen proactivator is identical to plasma prekallikrein.     

The Binding and Cleavage Characteristics of Human Hageman Factor during Contact Activation: A COMPARISON OF NORMAL PLASMA WITH PLASMAS DEFICIENT IN FACTOR XI, PREKALLIKREIN, OR HIGH MOLECULAR WEIGHT KININOGEN

The ability of human Hageman factor (coagulation factor XII) to bind to a glass surface and its susceptibility to limited proteolytic cleavage during the contact activation of plasma have been studied using normal human plasma and plasmas genetically deficient in factor XI, prekallikrein, or high molecular weight kininogen (HMWK). When diluted normal plasma containing ¹²⁵I-Hageman factor was exposed to a glass surface for varying times, the Hageman factor was found to bind to the surface, and within 5 min became maximally cleaved from its native 80,000 mol wt to yield fragments of 52,000 and 28,000 mol wt. Hageman factor in factor XI-deficient plasma behaved similarly. In prekallikrein-deficient plasma, the binding of Hageman factor to the glass surface occurred at the same rate as in normal plasma but the cleavage was significantly slower, and did not reach maximum until 60 min of incubation. Cleavage of Hageman factor in HMWK-deficient plasma occurred at an even slower rate, with greater than 110 min of incubation required for maximal cleavage, although the rate of binding to the glass was again the same as in normal plasma. Normal rates of cleavage of Hageman factor were observed for the deficient plasmas after reconstitution with purified human prekallikrein or HMWK, respectively. These observations suggest that normal contact activation in plasma is associated with proteolytic activation of surfacebound Hageman factor.     

Factor XII-induced fibrinolysis. Diminished proactivator activity and drastic reduction of activator activity in Fletcher factor-deficient plasma gamma globulin

Fibrinolytic studies in gamma G fractions of three Fletcher factor-deficient plasmas (functionally deficient in prekallikrein) revealed weak or no factor XII-independent activator activity. Two of the three Fletcher trait patients showed no plasminogen activator activity in clot lysis, fibrin plate, and amidolytic assays. The third patient showed no activator activity as determined by clot lysis and amidolytic assays but gave 10% of the activator activity detected in normal undiluted gamma G fraction in absence of HFf when determined by fibrin plate assay. Normal plasma gamma G fractions showed detectable and significant plasminogen activator activity. These fractions did not contain kallikrein or activated factor XI activities, thus indicating that the activator activity could not be attributed to the presence in these fractions or trace of these activated factors. Furthermore, factor XI-deficient plasma gamma G fraction, which was shown to contain no activated prekallikrein, showed normal plasminogen activator activity. Finally, specific antibodies to prekallikrein were shown not to quench the activity of plasminogen activator present in normal plasma gamma fraction. A double genetic deficiency to explain the absence in Fletcher factor-deficient plasma gamma G fractions of both prekallikrein proactivator and activator activities is not likely. Thus plasma prekallikrein, besides being a known plasminogen proactivator, appears to be required for the expression of a plasminogen activator activity.     

THE FIRST COMPONENT OF THE KININ-FORMING SYSTEM IN HUMAN AND RABBIT PLASMA : ITS RELATIONSHIP TO CLOTTING FACTOR XII (HAGEMAN FACTOR)

The isolation and characterization of the first component of the kinin-forming system in human and rabbit plasma are presented. Functionally, the molecule is the precursor of the activator of prekallikrein (Pre-PKA) and evidence is presented that it is identical with Hageman factor (clotting factor XII). The component from each plasma possessed similar characteristics. This molecule was found to have a mol wt of 110,000 and sedimentation rate of 4.6S. It migrated in electrophoresis as a β-globulin, having an isoelectric point of 6.1. Upon activation with glass, kaolin, diatomaceous earth, ellagic acid, or trypsin, the activated molecule converted purified prekallikrein (prokininogenase) to the active enzyme. Clot-promoting activity was associated with the capacity to activate prekallikrein through each procedure of isolation. The clot-promoting factor was in precursor form, requiring treatment with kaolin or trypsin to gain activity. Evidence indicated that the protein was Hageman factor (factor XII): it promoted clotting of factor XII-deficient, but not Factor XI- or IX-deficient plasma, and did not convert fibrinogen to fibrin it bound to and was activated by kaolin or other negatively charged particles in the presence of chelating agents; the activation by kaolin could be prevented by pretreating the kaolin with hexadimethrine bromide (H Br); prekallikrein-activating and clot-promoting activities were identical in their physical properties; and the prekallikrein activator could not be detected in Hageman factor-deficient plasma. Activation of Hageman factor was accompanied by cleavage of the molecule into several fragments, one of which possessed prekallikrein-activating (PKA) and clot-promoting properties. The PKA fragment sedimented at 2.6S and by gel filtration was found to have a molecular weight of 32,000. The PKA possessed only 1/50 the clot-promoting capacity of the freshly activated native molecule.     

Kininogen deficiency in Fitzgerald trait: role of high molecular weight kininogen in clotting and fibrinolysis.

Plasma from an asymptomatic person with defects in blood coagulation, release of kinin, and evolution of fibrinolytic activity upon contact with a foreign surface was deficient in kininogen. The coagulation defect was identified as "Fitzgerald trait." A preparation of high molecular weight kininogen repaired the defects in clotting, kinin release and fibrinolysis, but a preparation of low molecular weight kininogen did not. Therefore, Fitzgerald factor appears to be a high molecular weight kininogen. The site of action of the kininogen appears to be after that of activated Hageman factor and kallikrein in the generation of clot-promoting activity through activation of plasma thromboplastin antecedent (PTA).     

Flaujeac trait. Deficiency of human plasma kininogen.

Flaujeac trait plasma resembled Hageman trait or Fletcher trait, in that the intrinsic coagulation pathway, plasma fibinolytic pathway, kinin-forming system, permeability factor of dilution (PF/dil) phenomenon were abnormal. The defect in each assay was reconstituted by afactor separable from Hageman factor or Fletcher factor. This substance was an alpha-globulin with an approximate mol wt of 170,000. Flaujeac plasma did not release a kinin upon incubation with kallikrein and was deficient in total kininogen antigen. Antiserum to kininogen inhibited the activity of the factor in solution. Flaufeac factor was identified as a kininogen of high molecular weight (HMW-kininogen). The mean total kininogen antigen in four children of the proposita was 51% (range 34-62%) of normal. A functional coagulation assay of HMW-kininogen in the children was 34% (range 23-55%). The results were consistent with autosomal recessive inheritance. The plasma pathways of intrinsic coagulation, fibrinolysis, kinin formation, and PF/dil generation are dependent upon HMW-kininogen. We believe this is the first demonstration of biological function for a kininogen apart from its role as a substrate for kallikreins.     

Augmented Hageman factor and prolactin titers, enhanced cold activation of factor VII, and spontaneous shortening of prothrombin time in survivors of myocardial infarction

Hyperestrogenemia has been implicated in the pathophysiology of myocardial infarction. Because marked augmentation of the titer of Hageman factor is brought about by the administration of estrogens in humans and by prolactin or estrogen infusion in hypophysectomized rats, we measured the plasma concentrations of estradiol, prolactin, and clotting factors participating in surface-mediated reactions of coagulation in survivors of myocardial infarction. We observed higher titers of Hageman factor, prolactin, and high molecular weight kininogen but no significant change in estradiol or prekallikrein in survivors of myocardial infarction compared with controls. The titer of Hageman factor tended to be directly associated with the prolactin titer. We also report an increase in factor VII activity and spontaneous shortening of prothrombin time in the cold-stored plasma of survivors of myocardial infarction. In such individuals as well as in the control group, the titer of Hageman factor appeared to be responsible for half of the observed increase in factor VII activity and two thirds of the observed shortening of prothrombin time. These data indicate that although the titer of Hageman factor strongly influences the cold activation of factor VII, other factors may affect these phenomena.     

Studies on a complex mechanism for the activation of plasminogen by kaolin and by chloroform: the participation of Hageman factor and additional cofactors

As demonstrated by others, fibrinolytic activity was generated in diluted, acidified normal plasma exposed to kaolin, a process requiring Hageman factor (Factor XII). Generation was impaired by adsorbing plasma with glass or similar agents under conditions which did not deplete its content of Hageman factor or plasminogen. The defect could be repaired by addition of a noneuglobulin fraction of plasma or an agent or agents eluted from diatomaceous earth which had been exposed to normal plasma. The restorative agent, tentatively called Hageman factor-cofactor, was partially purified by chromatography and had an apparent molecular weight of approximately 165,000. It could be distinguished from plasma thromboplastin antecedent (Factor XI) and plasma kallikrein, other substrates of Hageman factor, and from the streptokinase-activated pro-activator of plasminogen. Evidence is presented that an additional component may be needed for the generation of fibrinolytic activity in mixtures containing Hageman factor, HF-cofactor, and plasminogen.The long-recognized generation of plasmin activity in chloroform-treated euglobulin fractions of plasma was found to be dependent upon the presence of Hageman factor. Whether chloroform activation of plasminogen requires Hageman factor-cofactor was not determined, but glass-adsorbed plasma, containing Hageman factor and plasminogen, did not generate appreciable fibrinolytic or caseinolytic activity.These studies emphasize the complex nature of the mechanisms which lead to the generation of plasmin in human plasma.     

Purification of High Molecular Weight Kininogen and the Role of This Agent in Blood Coagulation

Recent studies of individuals with high molecular weight (HMW) kininogen deficiency established the importance of this plasma protein for in vitro initiation of blood coagulation. In the present study, HMW-kininogen was highly purified from human plasma by monitoring its clot-promoting activity, using Fitzgerald trait plasma as a substrate. This preparation of HMW-kininogen revealed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (mol wt: 120,000) and released 1% of its weight as bradykinin upon incubation with plasma kallikrein. HMW-kininogen specifically repaired impaired surface-mediated plasma reactions of Fitzgerald trait plasma, but did not affect those of Hageman trait and Fletcher trait plasma. Kinin release from HMW-kininogen by trypsin, but not by plasma kallikrein, resulted in total loss of clot-promoting activity. No inhibitors of coagulation were found when all kinin activity was removed from HMW-kininogen by trypsin. The roles of HMW-kininogen, Hageman factor (HF, Factor XII), plasma prekallikrein (Fletcher factor), and plasma thromboplastin antecedent (PTA, Factor XI) in blood coagulation were studied in a purified system. HMW-kininogen was absolutely required for activation of PTA by HF and ellagic acid. The yield of activated PTA was proportional to the amount of HF, HMW-kininogen, and PTA in the mixtures, suggesting that, to activate PTA, these three proteins might form a complex in the presence of ellagic acid. No fragmentation of HF was found under these conditions. In contrast to HF, HF-fragments (mol wt: 30,000) activated PTA in the absence of HMW-kininogen and ellagic acid. Thus, it appears that in the present study PTA was activated in two distinct ways. Which pathway is the major one in whole plasma remains to be determined.     

A PREALBUMIN ACTIVATOR OF PREKALLIKREIN : II. DERIVATION OF ACTIVATORS OF PREKALLIKREIN FROM ACTIVE HAGEMAN FACTOR BY DIGESTION WITH PLASMIN

Activation of a plasma fraction containing unactivated Hageman factor and prekallikrein followed by chromatography of this fraction on DEAE-cellulose revealed four peaks having bradykinin-generating activity. Peak 1 contained kallikrein; peaks 2–3, 4, and 5 each contained prekallikrein-activating activity. Elution of peaks 2–3, 4, and 5 from disc gels after electrophoresis at pH 9.3 revealed peaks of prekallikrein-activating activity located at 5–8, 11–12, 15–16, and 20–26 mm, each of which was associated with a peak of clot-promoting activity which specifically corrected Hageman factor deficiency. Conversion of peak 2 to peaks 3, 4, and 5 was associated with a progressive decrease in size, increase in net negative charge, increased prekallikrein-activating activity, and decreased ability to correct Hageman factor deficiency. Plasminogen and plasmin were found on a DEAE-cellulose chromatogram of serum overlapping peaks 2 and 3. Incubation of active Hageman factor with streptokinase-activated plasminogen resulted in enhanced ability of the mixture to activate prekallikrein. Assessment of the products of this reaction by disc gel electrophoresis demonstrated the formation of the prealbumin prekallikrein activator corresponding to the major prekallikrein activator generated by contact activation of human plasma. The conversion of plasminogen to plasmin and the subsequent cleavage of Hageman factor by plasmin to form activators of prekallikrein represents one pathway in which coagulation, fibrinolysis, and inflammation are linked.     

Surface and fluid phase activities of two forms of activated Hageman factor produced during contact activation of plasma

The ability of the two forms of activated Hageman factor (HFa) produced during contact activation of plasma to activate prekallikrein and factor XI was studied. alpha-HFa, defined as an 80,000 mol wt two-chain enzyme which remains bound to the surface was capable of cleaving surface-bound prekallikrein and factor XI. beta-HFa, a 28,000 mol wt single chain molecule, released from the surface during contact activation was able to cleave prekallikrein but showed no activity on factor XI. Cleavage of prekallikrein by beta-HFa occurred irrespective of whether the substrate was surface-bound or in solution. Cleavage of factor XI occurred only when it was surface bound and only the alpha- form of HFa was capable of this proteolytic action. Factor XI was found to remain bound to the surface while prekallikrein and kallikrein rapidly dissociated from the surface into the supernate. These findings suggest that the initiation of intrinsic coagulation through the activation factor XI is a localized event occurring at the site of contact activation and is the result of the action of alpha-HFa. By contrast, kinin generation and fibrinolysis resulting from the formation of kallikrein can be initiated either at the site of contact activation, by alpha-HFa action, or throughout the plasma, by beta-HFa; further dissemination of these activities is assured by the rapid dissociation of kallikrein itself from the surface.     

Anaphylactic release of a prekallikrein activator from human lung in vitro.

We have demonstrated the in vitro IgE-mediated release of a prekallikrein activator from human lung. The lung prekallikrein activator was partially purified by sequential chromatography on sulfopropyl-Sephadex, DEAE-Sephacel, and Sepharose 6B. Purified human prekallikrein was converted to its active form (kallikrein) by the lung protease. The generated kallikrein was shown to be biologically active; that is, it generates bradykinin from purified human high-molecular weight kininogen and also cleaves benzoyl-propyl-phenyl-arginyl-p-nitroanilide, a known synthetic substrate of kallikrein. The lung prekallikrein activator differs from the known physiologic activators of prekallikrein (the activated forms of Hageman factor) with respect to: (a) size (it has a mol wt of approximately 175,000); (b) synthetic substrate specificity (D-propyl/phenyl/arginyl-p-nitroanilide is a substrate for the activated forms of Hageman factor, but not the lung protease); (c) antigenic specificity (an anti-Hageman factor immunoadsorbent column did not remove significant amounts of the lung protease, while it removed most of the activity of activated Hageman factor fragments); and (d) inhibition profile (the lung proteases was not inhibited by corn trypsin inhibitor). This prekallikrein activator provides a physiologic mechanism by which prekallikrein can be directly activated during IgE-mediated reactions of the lung. While the role of this lung prekallikrein activator in immediate hypersensitivity reactions and in other inflammatory processes is not clear, it does represent a first and important interface between IgE-mediated reactions and the Hageman factor-dependent pathways of the inflammatory response.