Blood coagulation initiation by a complement-mediated pathway

Complement and the prothrombotic state

In 2007 and 2009 the regulatory approval of the first-in-class complement inhibitor Eculizumab has revolutionized the clinical management of two rare, life-threatening clinical conditions: paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS). While being completely distinct diseases affecting blood cells and the glomerulus, PNH and aHUS remarkably share several features in their etiology and clinical presentation. An imbalance between complement activation and regulation at host surfaces underlies both diseases precipitating in severe thrombotic events that are largely resistant to anti-coagulant and/or anti-platelet therapies. Inhibition of the common terminal complement pathway by Eculizumab prevents the frequently occurring thrombotic events responsible for the high mortality and morbidity observed in patients not treated with anti-complement therapy. While many in vitro and ex vivo studies elaborate numerous different molecular interactions between complement activation products and hemostasis, this review focuses on the clinical evidence that links these two fields in humans. Several non-infectious conditions with known complement involvement are scrutinized for common patterns concerning a prothrombotic statues and the occurrence of certain complement activation levels. Next to PNH and aHUS, germline encoded CD59 or CD55 deficiency (the latter causing the disease Complement Hyperactivation, Angiopathic thrombosis, and Protein-Losing Enteropathy; CHAPLE), autoimmune hemolytic anemia (AIHA), (catastrophic) anti-phospholipid syndrome (APS, CAPS) and C3 glomerulopathy are considered. Parallels and distinct features among these conditions are discussed against the background of thrombosis, complement activation, and potential complement diagnostic and therapeutic avenues.

Abnormal platelet function in C3-deficient mice

SUMMARY BACKGROUND AND OBJECTIVES: The complement system is a biochemical cascade composed of several plasma proteins that can interact with endothelial cells and blood cells, including platelets. In order to investigate the effect of the complement system on platelets, we studied platelet function in C3-deficient mice that lack complement activity.

METHOD AND RESULTS

Tail-cut bleeding time was prolonged and platelet aggregation in response to protease-activated receptor-4 (PAR4) peptide was decreased in C3-deficient mice as compared with wild-type littermates. Platelet aggregation in response to other agonists (ADP and collagen) was similar between C3-deficient mice and their normal littermates. Isolated platelets from wild-type mice aggregate less in C3-deficient plasma than in normal plasma, and, conversely, addition of plasma from wild-type mice or plasma-purified C3 improved aggregation of C3-deficient platelets. We also monitored the formation of murine arteriole or venule thrombi in an intravital microscopy thrombosis model. We found that C3-deficient mice had a significantly delayed thrombotic response in arterioles as compared with their wild-type littermates. Furthermore, thrombi in C3-deficient mice were less stable and embolized more frequently than those in wild-type mice.

CONCLUSIONS

Platelets of C3-deficient mice have subnormal function, resulting in a prolonged tail-cut bleeding time and delayed thrombosis after vessel wall injury.

Fatal disseminated intravascular coagulation caused by Mycoplasma pneumoniae

We report fatal disseminated intravascular coagulation caused by Mycoplasma pneumoniae infection in a 7-year-old white boy. The diagnosis was based on relevant clinical material, absence of any other infections, a 4-fold rise in titer of complement fixation for M. pneumoniae and open lung biopsy findings. We discuss the association between M. pneumoniae and autoimmune mechanism.

Haematology in dengue and dengue haemorrhagic fever

Dengue fever (DF) and dengue haemorrhagic fever (DHF) are caused by the dengue virus. The major pathophysiological hallmark that distinguishes DHF from DF is plasma leakage as a result of increased vascular permeability. Following this leakage, hypovolaemic shock occurs as a consequence of a critical plasma volume loss. Constant haematological abnormalities occurring in DHF and frequently include bone marrow suppression, leucopenia and thrombocytopenia. An enhanced immune response of the host to a secondary DV infection is a feature of DHF and leads to many consequences. These are immune complex formation, complement activation, increased histamine release and a massive release of many cytokines into the circulation, leading to shock, vasculopathy, thrombopathy and disseminated intravascular coagulation (DIC). The mechanisms underlying the bleeding in DHF are multiple. These are vasculopathy, thrombopathy and DIC. Thrombopathy consists of thrombocytopenia and platelet dysfunction. DIC is prominent in patients with shock. The most severe DIC and massive bleeding are the result of prolonged shock and cause a fatal outcome. The mechanisms of thrombopathy and DIC and the proper management of DHF are reviewed and discussed.

Intraglomerular deposition of fibrin/fibrinogen-related antigen in children with various renal diseases

The localization of intraglomerular deposits of fibrin (Fb)/fibrinogen (Fg)-related antigen (FRA) in children with various glomerular diseases was determined by an immunohistopathologic method using an anti-Fg antibody capable of detecting FRA, an anti-D-dimer antibody capable of detecting crosslinked Fb (XLFb) and its derivatives (XLFbDP), and by a method using the effect of monochloroacetic acid (MCA) treatment on kidney sections. In proliferative glomerulonephritis (PGN), XLFbs were detected within the capillaries and extension beyond the mesangium was seen in severe PGN. The FRA within the mesangium of minimal or mild PGN was composed of the non-XLFb substance. The FRA within Bowman's space of most PGN had disappeared after MCA treatment, suggesting a non-XLFb substance. The presence of FRA within electron-dense deposits (EDD) suggested that FRA deposits are associated with immune-complex deposits in the glomeruli.

Role of terminal complement pathway in the heterologous phase of antiglomerular basement membrane nephritis

Terminal complement components, including the membrane attack complex, have been demonstrated in glomeruli of patients with immune complex and anti-GBM nephritis. We recently demonstrated the functional significance of C6 in the mediation of experimental membranous nephropathy in rabbits. In the present study, the role of C6 was examined in the heterologous phase of rabbit anti-GBM nephritis by studying normal and C6-deficient (C6D) rabbits. In C6D rabbits, C6 hemolytic activity was less than 0.01% of control. All control rabbits became heavily proteinuric in the first 24 hr following injection of a standard dose of sheep anti-rabbit GBM antibody (mean, 42.0 +/- 26.3; range, 18.4 to 83.5 mg protein/mg creatinine, N = 5). In contrast, C6D rabbits excreted a mean of only 5.1 +/- 5.5 mg/mg creatinine (range, 0.06 to 14.4, N = 6, P = 0.002). Protein excretion in normal rabbits was less than 0.06 mg/mg creatinine. Both control and C6D rabbits had similar deposits of sheep anti-rabbit GBM IgG in glomeruli when measured by radiolabeling techniques (control 15.8 +/- 2.71, N = 5; C6D 18.7 +/- 1.99 micrograms of sheep IgG/10(4) glomeruli, N = 6, P greater than 0.05). Control rabbits had a greater rise in serum creatinine in the first 24 hr (1.74 +/- 1.15 vs. 0.53 +/- 0.44 mg/dl, P less than 0.05). Both groups had similar deposits of sheep IgG and rabbit C3 by IF. By light microscopy at 4 and 24 hr, both groups had qualitatively similar proliferative changes and similar numbers of neutrophils infiltrating glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the terminal complement pathway in experimental membranous nephropathy in the rabbit

Our recent observations of a complement-mediated, cell-independent mechanism of altered glomerular permeability in rat membranous nephropathy suggested a possible role for the terminal complement pathway in the mediation of proteinuria in certain forms of glomerular disease. To directly determine whether the membranolytic terminal complement components (C5b-C9) are involved in glomerular injury, we studied the development of proteinuria in normal and C6-deficient (C6D) rabbits, in both of which a membranous nephropathy-like lesion develops early in the course of immunization with cationized bovine serum albumin (cBSA) (pI 8.9-9.2). C6 hemolytic activity of C6D was 0.01% that of control rabbits. After 1 wk of daily intravenous injections of cBSA, proteinuria developed in 71% of controls (median 154, range 1-3,010 mg/24 h, n = 24), whereas none of C6D were proteinuric (median 6, range 2-12 mg/24 h, n = 12, P less than 0.01). After 1 wk of cBSA, both groups had qualitatively identical glomerular deposits of BSA, rabbit IgG, and C3 on immunofluorescence microscopy, predominantly subepithelial electron-dense deposits on electron microscopy, and minimal glomerular inflammatory cell infiltration of glomeruli. Glomeruli were isolated from individual animals after 1 wk of cBSA and deposits of rabbit IgG antibody were quantitated by a standardized in vitro assay using anti-rabbit IgG-125I. Rabbit IgG deposits were found to be similar in control (29.8 +/- 13.2, range 12.7-48.6 micrograms anti-IgG/2,000 glomeruli, n = 6) and C6D rabbits (32.6 +/- 13.8, range 16.8-48.8 micrograms anti-IgG/2,000 glomeruli, n = 5, P greater than 0.05). After 2 wk, coincident with a prominent influx of mononuclear cells and neutrophils, proteinuria developed in C6D rabbits. These results document, for the first time, a requirement for a terminal complement component in the development of immunologic glomerular injury. Since the only known action of C6 is in the assembly of the membrane attack complex, these observations suggest that the membranolytic properties of complement may contribute to glomerular damage.

Evidence for complement-induced endothelial injury in vivo: a comparative ultrastructural tracer study in a controlled model of hyperacute rat cardiac allograft rejection

In order to delineate the potential role of platelet-derived factors and of the direct lytic action of complement in the pathogenesis of endothelial injury in hyperacute allograft rejection, a highly reproducible and rigidly controlled inbred rat cardiac model was studied, utilizing colloidal carbon as a vascular tracer for comparative ultrastructural analysis of the microcirculation. Unmodified allografts were characterized by widespread intramural carbon labeling of the microvasculature, which corresponded to sites of platelet sequestration and extensive endothelial cell disintegration. Under conditions of recipient platelet depletion without concomitant complement depression, carbon-labeled segments of the microcirculation showed widespread endothelial cell disintegration, the ultrastructural features of which were similar to those observed in the unmodified allograft group. The microvasculature of syngeneic heart grafts transplanted to platelet-depleted recipients as well as all platelet-depleted recipients' own hearts showed no similar ultrastructural changes. It is thus concluded that the loss of cellular integrity of the microcirculatory endothelium in hyperacute rat cardiac allograft rejection is not a platelet-dependent phenomenon. The current ultrastructural data combined with previous morphologic studies provide strong evidence that the severe form of endothelial injury observed in this model is mediated by the direct action of activated complement components.

Cryoglobulins, circulating immune complexes, and complement activation in cerebral malaria

A total of 32 patients with Plasmodium falciparum malaria were studied. Of these, 23 had benign infections, and 9 had typical cerebral malaria. Cryoglobulins, circulating immune complexes detected by a C1q-binding assay, and hypocomplementemia were found in eight of nine patients with cerebral malaria. Raised levels of complement component 3 breakdown products (C3d) were found in the seven patients tested. Peak levels of circulating immune complexes and C3d were associated with thrombocytopenia. In contrast, in patients with benign Plasmodium falciparum malaria, cryoglobulins and circulating immune complexes were found only in 3 of 23 patients. Similarly, hypocomplementemia was detected only in 5 of 23 patients. These observations suggest that the intensity of the immune response and of the associated complement activation may be important factors in the pathogenesis of cerebral malaria.

Effect of implant surface chemistry upon arterial thrombosis

A series of poly(alpha-amino acid)s with controlled chemical variations were investigated in order to assess the effect of different chemical moieties upon arterial thrombosis. The gross implant surface properties ranged from hydrophobic to hydrophilic ionic and nonionic. The materials were tested by implantation within canine femoral and carotid arteries. Results were compared with the response to the polyurethane Biomer. The changes in implant surface chemistry elicited a range of response that varied from intense thrombosis and rapid vessel occlusion to minimal thrombosis and endothelialization. The results showed that no simple relationship exists between a gross surface property, such as hydrophobicity, and the degree of thrombosis resistance. Some hydrophobic and hydrophilic materials were found to have good thrombosis resistance, while others were found to have poor thrombosis resistance. Leukocytes were shown to play an important role in both initial thrombosis and endothelialization. The major difference between materials that progressed to rapid vessel occlusion and materials that remained patent was the degree of direct leukocyte adherence and spreading on the implant surface prior to extensive platelet aggregation (less than 30 min). It was consistent for both hydrophobic and hydrophilic materials that the lack of direct leukocyte adherence to the implant surface was associated with intense thrombosis and rapid vessel occlusion. Conversely, the presence of numerous leukocytes directly adherent to either hydrophobic or hydrophilic surfaces appeared to have a moderating effect upon thrombosis and vessels with these implants remained patent. In instances when thrombosis was nonocclusive, the surfaces of the thrombi became endothelialized, primarily through the transformation of mononuclear leukocytes into endothelial cells. This article includes a hypothetical model representing the sequence of events and alternative pathways occurring at the blood-material interface, with special attention given to the involvement of leukocytes in arterial thrombosis.

The human complement system in thrombin-mediated platelet function

Thrombin-mediated platelet membrane-specific uptake of C3 and C5 was demonstrated by radiolabeled components and was visualized electron microscopically utilizing a ferritin marker conjugated to monospecific antibody to each component. The role of complement in thrombin-induced platelet function was determined. Though complement was not essential for thrombin-induced platelet aggregation and release of serotonin, these activities were significantly increased if complement was present. The release of serotonin was found to be a nonlytic process because under the conditions employed, no lactic dehydrogenase was released. The activation of complement was induced by a mechanism which has not been previously described. Thrombin associated with the platelet membrane presumably formed a C3 convertase that entered the known complement sequence at the C3 stage and proceeded to activate the terminal components through the known sequence to C9.

The "Hageman" connection: interrelationships of blood coagulation, fibrino(geno)lysis, kinin generation, and complement activation

The activation pathways for the generation of enzymes involved in blood clotting, clot lysis, complement activation, and kinin generation are briefly reviewed. The interrelationship of the four systems is illustrated by the multiple functions of four key enzymes: Factor XIIa, kallikrein, plasmin, and C1 esterase. The pivotal role of Factor XIIa in establishing this connection is elucidated.

Dermatitis gangrenosa infantum

A case of a 4-month-old girl with dermatitis gangrenosa infantum is reported. The lesions were seen on the cheeks and later at the site of blood examination on the earlobes. The patient was successfully treated with antibiotics and then by skin grafting.

The treatment of severe falciparum malaria

In severe falciparum malaria there is a pathophysiological cascade beginning with changes in the parasitized red blood cells which induce intermediate effects, in turn contributing to dysfunction of several organs. A low serum albumin is a common but often unrecognized finding which may contribute to oedema especially in the lung and brain. The only irreversible complication in falciparum malaria is the acute respiratory distress syndrome, manifested by cyanosis and rapid breathing, basically distinct from acute pulmonary oedema caused by therapeutic overhydration. The pathophysiology of falciparum malaria may be complex but the treatment is simple. Drugs, other than antimalarials, are rarely needed. Guidelines for cholorquine or quinine dosage in severe disease are proposed; each drug is given at a dose of 5 to 10 mg/kg in 10 ml/kg of fluid as an intravenous infusion in four hours at a frequency of dosing every 12 to 24 hours. When the disease has been brought under control the treatment should be changed from the intravenous to the oral route.

Formation of slow-reacting substance by guinea pig immunoglobulins

The capacity of guinea pig antibodies to mediate the antigen-induced release of slow-reacting substance (SRS) in the rat peritoneal cavity is restricted to IgG2 and, to a lesser extent, to IgG1 populations of immunoglobulin. IgM and homocytotropic antibody of the reaginic type lacked this activity. The process was partially blocked by previous decomplementation of the rats, was not affected by previous reduction of the circulating leukocytes, and was partially suppressed by previous depletion of circulating platelets with an antiserum to rat platelets.

Coagulation abnormalities in rheumatoid disease

Forty-one patients with rheumatoid arthritis, including 6 with acute vasculitis, 13 with chronic vasculitis, and 22 without vasculitis, were studied for evidence of intravascular coagulation and fibrinolysis (ICF). The mean plasma fibrinogen levels were elevated in all groups. The fibrinogen, platelet count, and fibrin split products were usually elevated in acute vasculitis. Fewer patients on corticosteroids had abnormal coagulation tests. Active plasmin was detected in 12 patients primarily with chronic vasculitis. Plasminogen activator activity was not diminished in vascular endothelium of normal appearing skin of those patients with or without vasculitis. None of the patients demonstrated decompensated intravascular coagulation and fibrinolysis. The results suggest overcompensated ICF occurring in rheumatoid arthritis, but rheumatoid patients with vasculitis cannot be clearly distinguished from those without vasculitis on the basis of the usual tests performed for coagulation and fibrinolysis abnormalities.

Complement and meningococcal infection

Serum C3 levels were measured in 211 patients with meningococcal disease. Low levels were found in 13 patients with acute meningococcaemia, and complement activation may have contributed to the peripheral circulatory collapse that was responsible for nine deaths. The complement profile of these patients suggested activation of both classical and alternative complement pathways. Patients with meningitis had a higher mean serum C3 level than controls. Serial studies in 13 serum antigen-positive patients with meningitis who subsequently developed arthritis or cutaneous vasculitis showed a transient fall in serum C3 in eight. This fall was probably due to the formation of immune complexes that were responsible for their allergic complications.

Effect of pneumococci on blood clotting, platelets, and polymorphonuclear leukocytes

Infections due to Streptococcus pneumoniae and products from the organism have been associated with alterations in blood clotting and function of platelets. Pneumococci and pneumococcal polysaccharide shortened the clotting times of whole blood, platelet-rich plasma (PRP), and platelet-poor plasma (PPP) in vitro. Clotting times of PPP and PRP from C6-deficient animals were likewise decreased. The bacteria had no effect on the one-stage prothrombin time or the partial thromboplastin time when the organisms were used as activating agents. Platelets aggregated in the presence of pneumococci, but aggregation was prevented by the addition of cyclic adenosine 3', 5'-monophosphate (cAMP). Furthermore, cAMP corrected the shortened clotting time of PRP in the presence of pneumococci. The clumping and release of polymorphonuclear coagulant that was induced by pneumococci was not prevented by cAMP. Thus, pneumococci exert several dose-dependent thromboplastic effects: (i) release of platelet thromboplastic substances; (ii) a direct thromboplastic effect; and (iii) release of polymorphonuclear coagulant.

Ultrastructural lesions on the surface of platelets associated with either blood coagulation or with antibody-mediated immune injury

During blood coagulation ultrastructural lesions were produced on the platelet membrane. They were dependent on the presence of both thrombin and complement (C) and were morphologically identical to the C-dependent ultrastructural lesions (type II) seen in red cells subsequent to activation of C by the alternate mechanismmthough similar in shape they differed in size from ultrastructural lesions (type I) PRODUCED BY ACTIVATION OF C via the classic mechanismmlesions of type I were seen on the platelet surface subsequent to antibody-dependent activation of the C system.

Origin of urinary fibrin/fibrinogen degradation products in glomerulonephritis

To elucidate the origin of the fibrin/fibrinogen degradation products (F.D.P.) occurring in the urine in glomerulonephritis 28 patients with glomerulonephritis were examined for renal fibrinolytic activity, F.D.P. in urine and serum, and blood fibrinolytic activators and blood fibrinolytic activators and inhibitors. Unlike the glomerful of healthy kidneys, which were fibrinolyticly inactive, those of kidneys with glomerulonephritis constantly showed fibrinolytic activity. The presence or absence of fibrin in the glomeruli was almost always accompanied by, respectively, the presence or absence of urinary F.D.P., which suggested a renal origin of urinary F.D.P. in glomerulonephritis. The low fibrinolytic activity of the blood and the absence of F.D.P. in the serum of these patients make it unlikely that the urinary F.D.P. in glomerulonephritis result from glomerular filtration.

Humoral immunostimulation. IV. Role of complement

When L cells were treated with anti-L-cell antibody in medium containing heat-inactivated fetal calf serum, nucleoside uptake and cell growth were stimulated. The response was markedly increased when fresh, unheated sera from calves, guinea pigs, humans, mice, or rabbits were also present. The factors in unheated serum responsible for the enhancement of immunostimulation were studied. Using low concentrations of sera deficient in various complement (C) components and low concentrations of antibody no augmentation of immunostimulation was seen with Clr-deficient human serum, C2-deficient human serum, C2,4-deficient human serum, C4-deficient guinea pig serum, C3-C9-depleted guinea pig serum (by administration of cobra venom factor to animals), but stimulation was observed with C5-deficient human serum, C5-deficient mouse serum, and C6-deficient rabbit serum. When the concentration of anti-serum was raised, however, augmentation was observed with C4-deficient guinea pig serum. Thus, at low concentrations of antiserum enhancement appeared to occur through the classical C pathway, whereas at high concentrations of antibody either the classical or alternate C pathways appeared to be involved. Stimulation was specifically restored by purified C2 in C2-deficient serum and by C3 in C3-C9-deficient serum. Under the usual reaction conditions consumption of guinea pig C component C4 could be demonstrated which provided direct evidence for activation of the classical C pathway under conditions leading to immunostimulation. By immunofluorescence, cells treated with antibody and normal human serum had human C3 deposited at the cell surface. Taken together these observations suggest that C activated through C3 by either the classical or alternate pathways has the potential to enhance nucleoside incorporation into DNA and cell growth of cells exposed to limiting amounts of antibody. Although the mechanism of stimulation is unknown, it is likely to involve a direct effect of C3 at the level of the cell membrane.

Effects of intravascular clotting on the activation of the complement system: The role of the platelet

Total hemolytic complement activity and the third component of complement were found to be significantly depressed in vivo in rabbits following the induction of disseminated intravascular coagulation by both thrombin and thromboplastin. Production of severe thrombocytopenia by the administration of platelet antiserum prior to the infusion of thrombin or thromboplastin partially prevented complement activation. The data show that, when clotting is triggered, complement activation takes place and that platelets are required to some extent for this reaction.

Potentiation of endotoxin-induced consumptive coagulopathy by lead acetate administration

Since chickens are naturally deficient in several clotting factors normally present in mammalian sera, the ability of lead acetate (PbAc(2)) to sensitize 11-day-old chicks to endotoxin was compared with its ability to sensitize rats. It was found that, although the chicks could tolerate only relatively low doses of PbAc(2), even those doses would produce a greater than 200-fold sensitization to the endotoxin in rats, as compared with little sensitization in the chicks. By using larger doses of PbAc(2), known to maximally sensitize rats to endotoxin, the effect of PbAc(2) sensitization on whole-blood clotting times, platelet counts, plasma factor V and VIII activities, and the appearance of fibrin degradation products was evaluated. It was found that animals treated with lethal doses of endotoxin but no PbAc(2) showed varying degrees of consumptive coagulopathy. On the other hand, the injection of minute quantities of endotoxin into PbAc(2)-sensitized rats invariably resulted in disseminated intravascular coagulation, apparently via a complete activation of the intrinsic pathway. It is concluded that the site of PbAc(2) sensitization to endotoxin is in the blood, and most probably at the level of Hageman factor activation.

Complement activation in children with acute malaria

Low C3 levels were found in the sera of most children with acute Plasmodium falciparum malaria. C4 and C1q levels were very low whilst glycine-rich β-glycoprotein (GBG) levels were only slightly depressed, suggesting that complement activation was occurring via the classical pathway. It is suggested that complement activation may play a part in initiating the complex series of changes that leads to the vascular damage seen in this infection.

Immunopathology of bullous pemphigoid. Basement membrane deposition of IgE, alternate pathway components and fibrin

Sixteen patients with bullous pemphigoid were examined using direct and indirect immunofluorescent techniques with antisera specific for C1q, C4, C3, C5, C3 proactivator, properdin, fibrinogen, IgA, IgM, IgG and IgE. The results of these studies are consistent with the activation of complement via the classical (antibody–C1q) sequence as well as via the alternate pathway. Fibrinogen and/or fibrin derivatives were demonstrated on the basement membrane of ten of fifteen patients tested and IgE basement membrane staining was found in four individuals.

Hereditary deficiency of the sixth component of complement in man. II. Studies of hemostasis

Prompted by previous observations of defective blood clotting in rabbits deficient in the sixth component of complement (C6), an evaluation was made of the hemostatic functions of the homozygous proband of a newly recognized human kindred with hereditary C6 deficiency. This human subject, who had no clinical evidence of a bleeding disorder, exhibited a total lack of C6 by functional and immunoprecipitin assays of serum or plasma. Standard tests of hemostatic function were normal; however, when the whole blood clotting time was measured at 25 degrees C in plastic tubes, it was at the upper range of our normal values. In confirmation of this observation, prothrombin consumption, when performed at 37 degrees C in plastic tubes, was at the lower range of normal. Inulin and endotoxin, in concentrations shown to cause activation of human complement, had little or no effect on clotting times or prothrombin consumption of normal or C6-deficient human blood. These observations indicate that absence of C6 does not have a significant effect on hemostatic function in man. In the light of other investigations, the observed differences in clotting function between C6-deficient human blood and C6-deficient rabbit blood could be due to species differences governing the susceptibility of platelets to complement activation.

Bacteroidaceae in thromboembolic disease: effects of cell wall components on blood coagulation in vivo and in vitro

The effects of Bacteroides sp., Fusobacterium mortiferum, Bacteroides fragilis, and Sphaerophorus necrophorus on various parameters of blood coagulation in vivo and in vitro were determined and compared to the coagulation effects of Escherichia coli and Salmonella minnesota, wild type and R595. Intravenous injection of washed cells, culture filtrate, lipopolysaccharide, or lipid A of the anaerobic gram-negative microorganisms into mice resulted in acceleration of coagulation. Lipopolysaccharide and lipid A of the anaerobic microorganisms had no apparent effect on circulating platelets in mice or rabbits and did not cause aggregation of human platelets in vitro. Washed cells, lipopolysaccharide, and lipid A of Bacteroides sp. and F. mortiferum also significantly accelerated the clotting time of recalcified platelet poor normal human plasma and C6-deficient rabbit plasma. Lipid A, but not lipopolysaccharide, of E. coli and washed cells of S. minnesota R595 accelerated coagulation by a similar mechanism. These results indicated that Bacteroides sp. and F. mortiferum can accelerate blood coagulation in vivo and in vitro by a mechanism which does not involve platelets or terminal components of complement.