Mice lacking serum amyloid P component do not necessarily develop severe autoimmune disease

Persistent lung inflammation and fibrosis in serum amyloid P component (APCs-/-) knockout mice

Fibrosing diseases, such as pulmonary fibrosis, cardiac fibrosis, myelofibrosis, liver fibrosis, and renal fibrosis are chronic and debilitating conditions and are an increasing burden for the healthcare system. Fibrosis involves the accumulation and differentiation of many immune cells, including macrophages and fibroblast-like cells called fibrocytes. The plasma protein serum amyloid P component (SAP; also known as pentraxin-2, PTX2) inhibits fibrocyte differentiation in vitro, and injections of SAP inhibit fibrosis in vivo. SAP also promotes the formation of immuno-regulatory Mreg macrophages. To elucidate the endogenous function of SAP, we used bleomycin aspiration to induce pulmonary inflammation and fibrosis in mice lacking SAP. Compared to wildtype C57BL/6 mice, we find that in Apcs^-/- “SAP knock-out” mice, bleomycin induces a more persistent inflammatory response and increased fibrosis. In both C57BL/6 and Apcs^-/- mice, injections of exogenous SAP reduce the accumulation of inflammatory macrophages and prevent fibrosis. The types of inflammatory cells present in the lungs following bleomycin-aspiration appear similar between C57BL/6 and Apcs^-/- mice, suggesting that the initial immune response is normal in the Apcs^-/- mice, and that a key endogenous function of SAP is to promote the resolution of inflammation and fibrosis.

Pentraxins: structure, function, and role in inflammation

The pentraxins are an ancient family of proteins with a unique architecture found as far back in evolution as the Horseshoe crab. In humans the two members of this family are C-reactive protein and serum amyloid P. Pentraxins are defined by their sequence homology, their pentameric structure and their calcium-dependent binding to their ligands. Pentraxins function as soluble pattern recognition molecules and one of the earliest and most important roles for these proteins is host defense primarily against pathogenic bacteria. They function as opsonins for pathogens through activation of the complement pathway and through binding to Fc gamma receptors. Pentraxins also recognize membrane phospholipids and nuclear components exposed on or released by damaged cells. CRP has a specific interaction with small nuclear ribonucleoproteins whereas SAP is a major recognition molecule for DNA, two nuclear autoantigens. Studies in autoimmune and inflammatory disease models suggest that pentraxins interact with macrophage Fc receptors to regulate the inflammatory response. Because CRP is a strong acute phase reactant it is widely used as a marker of inflammation and infection.

Inhibition of TTR aggregation-induced cell death--a new role for serum amyloid P component

Background

Serum amyloid P component (SAP) is a glycoprotein that is universally found associated with different types of amyloid deposits. It has been suggested that it stabilizes amyloid fibrils and therefore protects them from proteolytic degradation.

Methodology/Principal Findings

In this paper, we show that SAP binds not only to mature amyloid fibrils but also to early aggregates of amyloidogenic mutants of the plasma protein transthyretin (TTR). It does not inhibit fibril formation of TTR mutants, which spontaneously form amyloid in vitro at physiological pH. We found that SAP prevents cell death induced by mutant TTR, while several other molecules that are also known to decorate amyloid fibrils do not have such effect. Using a Drosophila model for TTR-associated amyloidosis, we found a new role for SAP as a protective factor in inhibition of TTR-induced toxicity. Overexpression of mutated TTR leads to a neurological phenotype with changes in wing posture. SAP-transgenic flies were crossed with mutated TTR-expressing flies and the results clearly confirmed a protective effect of SAP on TTR-induced phenotype, with an almost complete reduction in abnormal wing posture. Furthermore, we found in vivo that binding of SAP to mutated TTR counteracts the otherwise detrimental effects of aggregation of amyloidogenic TTR on retinal structure.

Conclusions/Significance

Together, these two approaches firmly establish the protective effect of SAP on TTR-induced cell death and degenerative phenotypes, and suggest a novel role for SAP through which the toxicity of early amyloidogenic aggregates is attenuated.

A locked nucleic acid clamp-mediated PCR assay for detection of a p53 codon 249 hotspot mutation in urine

Hepatocellular carcinoma (HCC) has a 5-year survival rate of <10% because it is difficult to diagnose early. Mutations in the TP53 gene are associated with approximately 50% of human cancers. A hotspot mutation, a G:C to T:A transversion at codon 249 (249T), may be a potential DNA marker for HCC screening because of its exclusive presence in HCC and its detection in the circulation of some patients with HCC. A locked nucleic acid clamp-mediated PCR assay, followed by melting curve analysis (using the SimpleProbe), was developed to detect the TP53 249T mutation. In this assay, the locked nucleic acid clamp suppressed 10(7) copies of wild-type templates and permitted detection of 249T-mutated template, with a sensitivity of 0.1% (1:1000) of the mutant/wild-type ratio, assessed by a reconstituted standard within 2 hours. With an amplicon size of 41 bp, it detects target DNA sequences in short fragmented DNA templates. The detected mutations were validated by DNA sequencing analysis. We then tested DNA isolated from urine samples of patients with HCC for p53 mutations and identified positive TP53 mutations in 9 of 17 samples. The possibility of using this novel TP53 249T assay to develop a urine or blood test for HCC screening is discussed.

Current and emerging strategies for the treatment and management of systemic lupus erythematosus based on molecular signatures of acute and chronic inflammation

Lupus is a chronic, systemic inflammatory condition in which eicosanoids, cytokines, nitric oxide (NO), a deranged immune system, and genetics play a significant role. Our studies revealed that an imbalance in the pro- and antioxidants and NO and an alteration in the metabolism of essential fatty acids exist in lupus. The current strategy of management includes administration of nonsteroidal anti-inflammatory drugs such as hydroxychloroquine and immunosuppressive drugs such as corticosteroids. Investigational drugs include the following: 1) belimumab, a fully human monoclonal antibody that specifically recognizes and inhibits the biological activity of B-lymphocyte stimulator, also known as B-cell-activation factor of the TNF family; 2) stem cell transplantation; 3) rituximab, a chimeric monoclonal antibody against CD20, which is primarily found on the surface of B-cells and can therefore destroy B-cells; and 4) IL-27, which has potent anti-inflammatory actions. Our studies showed that a regimen of corticosteroids and cyclophosphamide, and methods designed to enhance endothelial NO synthesis and augment antioxidant defenses, led to induction of long-lasting remission of the disease. These results suggest that methods designed to modulate molecular signatures of the disease process and suppress inflammation could be of significant benefit in lupus. Some of these strategies could be vagal nerve stimulation, glucose-insulin infusion, and administration of lipoxins, resolvins, protectins, and nitrolipids by themselves or their stable synthetic analogs that are known to suppress inflammation and help in the resolution and healing of the inflammation-induced damage. These strategies are likely to be useful not only in lupus but also in other conditions, such as rheumatoid arthritis, scleroderma, ischemia-reperfusion injury to the myocardium, ischemic heart disease, and sepsis.

Binding of human serum amyloid P componentto L-selectin

Serum concentrations of soluble L-selectin by far exceed those of other soluble adhesion molecules, and serum soluble L-selectin concentrations are remarkably stable upon prolonged storage. We present evidence for Ca(2+)-dependent binding interactions between human serum amyloid P (SAP), a proteolysis-resistant pentraxin glycoprotein, and L-selectin, as shown by surface plasmon resonance measurements, protein band shift assays in a native PAGE system, and after SDS-PAGE and membrane transfer. Monoclonal antibodies to L-selectin strongly reduced binding of biotinylated SAP to L-selectin-IgG chimeras immobilized on microtiter plates. As binding was reduced by prior glycopeptidase F treatment of L-selectin but not of SAP, it appears to be based on SAP lectin domain interactions with N-linked L-selectin carbohydrates. In freshly prepared human lymphocytes, SAP incubation induced expression of a beta2 integrin neoepitope associated with high-affinity binding. This was partially blocked by pre-incubation with Fab fragments of two anti-L-selectin antibodies. In flow chamber experiments, SAP inhibited the adherence of human neutrophils to activated endothelium under shear stress. Thus, SAP binds to human L-selectin and affects L-selectin-dependent leukocyte-endothelial interactions.

Anti-serum amyloid component P antibodies in patients with systemic lupus erythematosus correlate with disease activity

OBJECTIVE

To determine the presence of raised titres of anti-serum amyloid P component (SAP) antibodies in patients with systemic lupus erythematosus (SLE) and to evaluate their correlation with clinical disease by the SLEDAI and clinical manifestations.

METHODS

452 samples were screened for raised anti-SAP antibody titres by an ELISA. Clinical measures and SLEDAI scores were independently reviewed from medical records. 21 serial samples from 7 patients with SLE were assessed for a change in anti-SAP antibody titres after treatment.

RESULTS

Raised anti-SAP antibody titres were detected in 145/328 (44%) SLE samples. In 112 randomly selected samples, 69/112 (62%) patients had raised anti-SAP antibodies and anti-dsDNA antibody titres, whereas only 32/112 (28%) had raised anti-dsDNA antibody titres without raised anti-SAP antibody titres. The mean titre of anti-SAP antibodies in patients with active disease was higher than in patients with inactive disease and controls. SLEDAI scores, assessed in 54 patients, were raised in 26/31 (84%) patients with raised anti-SAP antibody titres. A SLEDAI score >or=8 was found in 16/31 (52%) patients with raised anti-SAP antibody titres but in only 5/23 (22%) patients without raised titres. No specific pattern of disease was detected in patients with or without raised titres of anti-SAP antibodies. Serial sampling from patients with active SLE and raised anti-SAP antibody titres showed that anti-SAP antibody titres decreased after treatment and correlated with clinical improvement.

CONCLUSION

Raised anti-SAP antibody titres detected in patients with SLE correlate with disease activity and decrease with improvement of clinical disease, and thus may serve as an additional prognostic marker.

Proteomic analysis of protein adsorption: Serum amyloid P adsorbs to materials and promotes leukocyte adhesion

Serum and plasma protein adsorption on materials was analyzed using gel electrophoresis and ion trap mass spectrometry. Following incubation of polypropylene, polyethylene terephthalate (PET), or polydimethylsiloxane (PDMS) with 5% serum for longer than 4 h, we found unexpectedly high amounts of the pentraxin serum amyloid P. It was previously shown that serum amyloid P is constitutively expressed in humans, functions as an opsonin, and interacts with the Fcgamma receptors on leukocytes. We demonstrate that serum amyloid P adsorbed to tissue culture polystyrene, PDMS, and PET promotes the adhesion of granulocytes and monocytes in the presence of calcium. The methods developed for these studies may be useful for the large-scale study of protein adsorption and do not rely on radiolabeling or the availability of antibodies.

Human serum amyloid P component attenuates the bacterial lipopolysaccharide-induced increase in blood-brain barrier permeability in mice

Endotoxin challenge leads to septic shock, multi-organ failure and death in mice. Permeability of the blood-brain barrier (BBB) is increased by endotoxemia. Serum amyloid P component (SAP) is a lipopolysaccharide (LPS)-binding protein that can modulate the host reactions during infections. It is controversial whether SAP can protect from LPS toxicity in vivo or not. We have tested the effect of human SAP on BBB permeability of Salmonella typhimurium LPS-injected mice. The animals showed signs of sickness behaviour including immobility, anorexia, and diarrhoea. Intraperitoneally administered LPS increased the BBB permeability for sodium fluorescein for about 4-fold, and for albumin for more than 2-fold in brain cortex. SAP, given intravenously, had no effect on basal BBB permeability for albumin, although it decreased sodium fluorescein extravasation to brain tissue. In LPS-treated mice, SAP administration alleviated the symptoms of septic shock, and significantly inhibited the enhanced BBB permeability for both tracers. Our data indicate that human SAP may counteract the toxic effects of LPS during septic shock.

Triggers for anti-chromatin autoantibody production in SLE

The formation of autoantibodies against chromatin is the main feature of systemic lupus erythematosis (SLE), an autoimmune disease, which is T-cell dependent and autoantigen-driven. Historically, antibodies against dsDNA, one of the components of chromatin, are considered as a hallmark of SLE. However, dsDNA is poorly immunogenic. Nucleosome-specific T helper cells have been identified. These T cells propagate not only nucleosome-specific antibodies, but also anti-dsDNA antibodies. Nucleosomes are formed during apoptosis by cleavage of chromatin, and evidence of disturbed apoptosis has been found especially in certain murine models of lupus. In addition to an increased rate of apoptosis, autoimmunity against chromatin might also result from an impaired phagocytosis of apoptotic material, for which strong evidence has been provided by studies in certain knock-out mice (C1q, SAP, Dnase I). The induction of an immune response to nucleosomes could be enhanced by modifications of histones or DNA during apoptosis, altered presentation by antigen presenting cells or a viral infection. The release of nucleosomes and the formation of anti-chromatin autoantibodies result in formation of complexes, which bind to the glomerular basement membrane via heparan sulfate. This deposition incites glomerulonephritis, the most serious manifestation of SLE.

Mannose binding lectin (MBL) polymorphisms associated with low MBL production in patients with dermatomyositis

One theory for the pathophysiology of photosensitive autoimmune skin diseases is that photoinduction of tumor necrosis factor alpha (TNFalpha) secretion leads to keratinocyte apoptosis and translocation of previously sequestered cellular antigens that then activate the immune system. We previously found an association of the overproducing TNFalpha-308 A variant with adult dermatomyositis and with subacute cutaneous lupus erythematosus. Here we focused on mannose binding lectin (MBL), which is one of several proteins involved in clearance of apoptotic cells and could thereby lessen photosensitive autoimmunity. We examined three variant MBL polymorphisms associated with decreased MBL protein (Asp54, Glu57, and the LX promoter polymorphism) in adult dermatomyositis, subacute cutaneous lupus erythematosus, and discoid lupus, and controls. The variant Asp54 allele was positively associated with adult dermatomyositis in a dose-responsive fashion (p=0.0004), as was the Glu57 allele (p=0.004). None of the three variant MBL alleles considered individually was significantly associated with either subacute cutaneous lupus erythematosus or discoid lupus. In adult dermatomyositis patients homozygous for the wild-type TNFalpha-308G allele (GG), i.e., presumably without elevated TNFalpha production, 69% had at least two of the MBL polymorphisms, versus 20% of healthy GG controls (p=0.0011). Combinations of low-producing MBL variants were over-represented in adult dermatomyositis in a dose-responsive fashion (p=0.0002). In adult dermatomyositis patients with one variant TNFalpha-308 A allele (GA), 46% had at least two MBL polymorphisms, versus 7% of GA controls (p=0.0077). Thus, low-producing MBL genes are very strongly associated with adult dermatomyositis. Our model is that genetic polymorphisms leading to overproduction of apoptotic keratinocytes and then impaired clearance of these cells contribute to the pathogenesis of adult dermatomyositis, a photoinduced autoimmune skin disease.

Serum amyloid P component and C-reactive protein opsonize apoptotic cells for phagocytosis through Fcgamma receptors

Serum amyloid P component (SAP) and C-reactive protein (CRP) are opsonins that react with nuclear autoantigens targeted in systemic autoimmunity. CRP and SAP bind to apoptotic and necrotic cells, which are potential sources of these autoantigens. We have recently determined that the receptors for CRP on phagocytic cells are Fcgamma receptors. The goal of this study was to determine whether CRP and SAP promote phagocytosis of apoptotic cells and to identify the receptors involved. Apoptosis was induced in human neutrophils (PMN) and the Jurkat T-cell line by UV-irradiation. SAP treatment of apoptotic human PMN increased ingestion by autologous macrophages. Both SAP and CRP increased ingestion of apoptotic, but not normal Jurkat cells by J-774 macrophages and mouse peritoneal macrophages. Neither SAP nor CRP increased ingestion of apoptotic Jurkat cells by macrophages from FcR gamma-chain deficient mice, which lack FcgammaRI and FcgammaRIII. Inhibition of FcgammaRIII-mediated uptake using mAb 2.4G2 eliminated opsonization by SAP, but not by CRP. These results indicate that pentraxins promote uptake of apoptotic cells through FcgammaRI and/or FcgammaRIII. Ingestion through these receptors is expected to alter the pattern of cytokine production and antigen presentation in response to apoptotic cells.