Ancrod improves survival in murine systemic lupus erythematosus

Targeted deletion of fgl2 leads to impaired regulatory T cell activity and development of autoimmune glomerulonephritis

Mice with targeted deletion of fibrinogen-like protein 2 (fgl2) spontaneously developed autoimmune glomerulonephritis with increasing age, as did wild-type recipients reconstituted with fgl2-/- bone marrow. These data implicate FGL2 as an important immunoregulatory molecule and led us to identify the underlying mechanisms. Deficiency of FGL2, produced by CD4+CD25+ regulatory T cells (Treg), resulted in increased T cell proliferation to lectins and alloantigens, Th 1 polarization, and increased numbers of Ab-producing B cells following immunization with T-independent Ags. Dendritic cells were more abundant in fgl2-/- mice and had increased expression of CD80 and MHCII following LPS stimulation. Treg cells were also more abundant in fgl2-/- mice, but their suppressive activity was significantly impaired. Ab to FGL2 completely inhibited Treg cell activity in vitro. FGL2 inhibited dendritic cell maturation and induced apoptosis of B cells through binding to the low-affinity FcgammaRIIB receptor. Collectively, these data suggest that FGL2 contributes to Treg cell activity and inhibits the development of autoimmune disease.

Treatment of lupus nephritis

Renal involvement in systemic lupus erythematosus (SLE) is a serious complication of the disease. However, the prognosis of patients with lupus nephritis is continually improving with 10-year survival rates now greater than 75%. This improvement reflects earlier diagnosis due to more sensitive and specific diagnostic tests, better clinical appreciation of the natural history, and improved treatment of SLE and its manifestations. This review of the treatment of lupus nephritis has graded the level of evidence of specific treatment using the guidelines of the US Preventive Service Task Force. Although many new treatments have been advocated, the best evidence for treating proliferative lupus nephritis relies on a strategy combining specific treatment of the SLE as well as generalised treatment of the associated comorbidities. This strategy involves a combination of corticosteroids and cytotoxic agents plus or minus the adjunctive use of antimalarials, coordinated aggressive management of hypertension, proteinuria, infections, dyslipidaemia, thrombotic coagulopathy and potential renal replacement therapies.

Roles for thrombin and fibrin(ogen) in cytokine/chemokine production and macrophage adhesion in vivo

Extravascular coagulation leading to fibrin deposition accompanies many immune and inflammatory responses. Although recognized by pathologists for decades, and probably pathologic under certain conditions, the physiologic functions of extravascular coagulation remain to be fully defined. This study demonstrates that thrombin can activate macrophage adhesion and prompt interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1) production in vivo. Peritoneal macrophages were elicited with thioglycollate (TG) and then activated in situ, either by intraperitoneal injection of lipopolysaccharide (LPS) or by injection of antigen into mice bearing antigen-primed T cells. Others previously established that such treatments stimulate macrophage adhesion to the mesothelial lining of the peritoneal cavity. The present study demonstrates that thrombin functions in this process, as macrophage adhesion was suppressed by Refludan, a highly specific thrombin antagonist, and induced by direct peritoneal administration of purified thrombin. Although recent studies established that protease activated receptor 1 (PAR-1) mediates some of thrombin's proinflammatory activities macrophage adhesion occurred normally in PAR-1-deficient mice. However, adhesion was suppressed in fibrin(ogen)-deficient mice, suggesting that fibrin formation stimulates macrophage adhesion in vivo. This study also suggests that fibrin regulates chemokine/cytokine production in vivo, as direct injection of thrombin stimulated peritoneal accumulation of IL-6 and MCP-1 in a fibrin(ogen)-dependent manner. Given that prior studies have clearly established inflammatory roles for PAR-1, thrombin probably has pleiotropic functions during inflammation, stimulating vasodilation and mast cell degranulation via PAR-1, and activating cytokine/chemokine production and macrophage adhesion via fibrin(ogen).

Identification of a unique glomerular factor X activator in murine lupus nephritis

The role of glomerular procoagulant activity (PCA) was studied in mice (MRL/lpr, NZBxWF,, and BXSB) that are known to develop lupus nephritis. In young mice (6 to 8 wk) without renal disease, there was no increase in spontaneous glomerular PCA. In contrast, older (5 to 8 mo) autoimmune mice had significant augmentation in glomerular PCA, coinciding with the histologic appearance of severe glomerulonephritis and renal fibrin deposition. The PCA was characterized as a serine protease that directly activated factor X. This factor X activator is not tissue factor because (1) expression of PCA was not dependent on factor VII; (2) a monoclonal antibody against the factor X activator inhibited glomerular PCA, but not tissue factor; (3) the molecular weight (66 kD) of the activator was different from that of tissue factor; and (4) concanavalin A inhibited tissue factor but not glomerular PCA. Immunohistochemical studies localized the factor X activator to the glomerular mesangium and capillary wall of 4- to 6-mo-old diseased MRL/lpr mice. Immunogold-labeled antibody bound to the dense deposits, macrophages, and endothelial cells of diseased glomeruli. These studies define the role of a unique glomerular factor X activator in murine lupus nephritis.

Strategies to prevent thrombosis in xenotransplants

Coagulation remains a major barrier to successful xenotransplantation. Identification of the role of complement activation in HAR and prevention of complement activation by high expression of DAF and CD59 has largely overcome HAR. Understanding the molecular basis of DXR and identification of novel strategies to prevent activation of endothelial cells using monoclonal antibodies, soluble inhibitors of coagulation, vaccination, antisense constructs, and recombinant DNA technology offers the promise of overcoming the thrombosis associated with xenotransplantation.

The glomerular basement membrane in lupus nephritis

Systemic lupus erythematosus is a disease that is particularly suited for studies of glomerular basement membrane pathology. Classification of the renal pathology of lupus nephritis is usually based on light microscopic features, combined with immunofluorescence findings and electron microscopic alterations. Study of renal biopsy helps to distinguish potentially reversible and irreversible disease, and to estimate prognosis of patients with lupus nephritis. Moreover, studies of human disease, as well as the availability of animal models and in vitro cell culture systems employing biochemical and molecular biological studies of extracellular matrix, have led to a considerable increase in knowledge of the pathogenetic events underlying derangements of the glomerular basement membrane in lupus nephritis.

Fibrin(ogen) mediates acute inflammatory responses to biomaterials

Although "biocompatible" polymeric elastomers are generally nontoxic, nonimmunogenic, and chemically inert, implants made of these materials may trigger acute and chronic inflammatory responses. Early interactions between implants and inflammatory cells are probably mediated by a layer of host proteins on the material surface. To evaluate the importance of this protein layer, we studied acute inflammatory responses of mice to samples of polyester terephthalate film (PET) that were implanted intraperitoneally for short periods. Material preincubated with albumin is "passivated," accumulating very few adherent neutrophils or macrophages, whereas uncoated or plasma-coated PET attracts large numbers of phagocytes. Neither IgG adsorption nor surface complement activation is necessary for this acute inflammation; phagocyte accumulation on uncoated implants is normal in hypogammaglobulinemic mice and in severely hypocomplementemic mice. Rather, spontaneous adsorption of fibrinogen appears to be critical: (a) PET coated with serum or hypofibrinogenemic plasma attracts as few phagocytes as does albumin-coated material; (b) in contrast, PET preincubated with serum or hypofibrinogenemic plasma containing physiologic amounts of fibrinogen elicits "normal" phagocyte recruitment; (c) most importantly, hypofibrinogenemic mice do not mount an inflammatory response to implanted PET unless the material is coated with fibrinogen or the animals are injected with fibrinogen before implantation. Thus, spontaneous adsorption of fibrinogen appears to initiate the acute inflammatory response to an implanted polymer, suggesting an interesting nexus between two major iatrogenic effects of biomaterials: clotting and inflammation.

Platelet-activating factor modulates endotoxin-induced macrophage procoagulant activity by a protein kinase C-dependent mechanism

Macrophage procoagulant activity is an important mediator of extravascular fibrin deposition at sites of infection and appears to contribute to the pathogenesis of several infectious disease processes. Previous studies have shown that the inflammatory mediator platelet-activating factor was able to prime macrophages for induction of procoagulant activity by bacterial lipopolysaccharide. The present studies were designed to examine the mechanism of this priming effect. Platelet-activating factor (100 nM) primed macrophages for procoagulant activity generation in response to endotoxin at concentrations as low as 100 ng/ml and also following exposure to Escherichia coli, Bacteroides fragilis, and Staphylococcus aureus. The priming effect occurred following a pretreatment with platelet-activating factor for as short as 1 min, suggesting a rapid activation event. Two different doses of the calcium ionophore ionomycin were used to mimic the peak and sustained effects of platelet-activating factor on cytoplasmic calcium levels (1 microM and 100 nM, respectively). Neither dose was able to mimic the priming effect. However, extracellular calcium was necessary for induction of procoagulant activity and the priming effect. By contrast, the protein kinase C agonist phorbol myristate acetate reproduced the priming phenomenon observed for platelet-activating factor. In further support of the concept that protein kinase C activation mediated the effect of platelet-activating factor, the specific protein kinase C inhibitor staurosporine reversed the ability of platelet-activating factor to augment induction of macrophage procoagulant activity by endotoxin. These data suggest mechanisms by which inflammatory mediators within the microenvironment of infection might modulate the host response to bacterial pathogens.

Extravascular fibrin formation and dissolution in synovial tissue of patients with osteoarthritis and rheumatoid arthritis

Fibrin deposition is a prominent finding in the synovium of patients with rheumatoid arthritis (RA). Macrophages are found in increased numbers in RA synovium, and these cells are known to produce a variety of procoagulant and anticoagulant molecules. Using immunohistologic techniques, the content and distribution of several important components of the coagulation system in the synovium of patients with RA, osteoarthritis (OA), or traumatic joint abnormalities requiring surgery were investigated. Samples from 3 patients from each category were examined in detail. RA synovium (compared with that of patients with OA or joint trauma) had increased numbers of macrophages and increased expression/content of fibrinogen, tissue factor, factor XIII, tissue transglutaminase, cross-linked fibrin (fibrin D dimer), urokinase-type plasminogen activator, and alpha 2-plasmin inhibitor. Macrophage content in RA synovium was increased in both the lining cell areas and the interstitial cell areas. Fibrinogen was distributed throughout the tissue in all samples and was greater in RA synovium. In trauma and OA synovia, tissue factor was seen only in association with vessels (endothelial cells), but in RA synovium, it was markedly increased throughout the tissues. While fibrin D dimer was seen in small amounts in synovial lining cell areas of trauma and OA synovia, it was present in increased amounts in the lining cell and interstitial cell areas of RA synovium. Factor XIII and tissue transglutaminase were present in scant amounts in trauma and OA synovia, but there were increased amounts of both (especially tissue transglutaminase) in RA synovium in the vessel, lining cell, and interstitial cell areas. Urokinase and alpha 2-plasmin inhibitor were also markedly increased in RA synovium. These results suggest that in inflamed synovium, there is ongoing extravascular tissue fibrin formation and dissolution that correlates with the degree of inflammation and macrophage content. Extravascular coagulation/fibrinolysis in RA represents a potential target for therapeutic intervention in this disease.