Surface blebs on apoptotic cells are sites of enhanced procoagulant activity: implications for coagulation events and antigenic spread in systemic lupus erythematosus

Circulating endothelial cells in malignant disease

Cancer is a disease largely dependent on neoangiogenesis. Cancer neoangiogenesis is often disordered and abnormal, with evidence of coexisting vascular endothelial dysfunction. A novel method of assessing vascular endothelial function in cancer is via the quantification of circulating endothelial cells (CEC). Unusual in healthy individuals, their presence in elevated numbers often indicates substantial vascular endothelial perturbation. Another interesting cell type is the endothelial progenitor cell (EPC), whose numbers increase in the presence of vascular damage. Recent research suggests that EPCs have an important role in tumor vasculogenesis. Another marker being investigated in the context of vascular dysfunction and coagulopathy is the endothelial microparticle (EMP). Thus, CECs, EPCs and EMPs may represent potentially novel methods for evaluating the vascular status of cancer patients. This review will summarize the current position of CECs, EPCs and EMPs in cell biology terms, with particular emphasis on their relationship to malignant disease.

Association between anti-nucleophosmin and anti-cardiolipin antibodies in (NZW x BXSB)F1 mice and human systemic lupus erythematosus

We showed previously that nucleophosmin (NPM), a nucleolar phosphoprotein, is recognized by sera from (NZW x BXSB)F1 (WB) mice, a model of systemic lupus erythematosus (SLE) and anti-phospholipid syndrome. In the present study we analysed the prevalence and kinetics of anti-NPM autoantibodies in WB mice by a solid-phase ELISA with recombinant human (rh) NPM as the antigen and showed that most male WB mouse sera had anti-NPM antibodies that were responsible for their indirect immunofluorescence staining pattern on Hep-2 cells. Anti-NPM antibodies were significantly associated with anti-cardiolipin (aCL) antibodies. This antibody profile mirrored that observed in certain human SLE sera because anti-NPM antibodies were detected in 28% of the sera from patients with SLE and were similarly associated with aCL antibodies. The demonstration that rhNPM bound to cardiolipin (CL) in vitro and increased the CL-binding activity of a WB-derived aCL monoclonal antibody indicates that NPM can interact with CL to form SLE-related immunogenic particles that might be responsible for the concomitant production of anti-NPM and aCL antibodies.

Proteome of endothelial cell-derived procoagulant microparticles

Microparticles (MP) are small membrane vesicles that are released from cells upon activation or during apoptosis. Cellular MP in body fluids constitute a heterogeneous population, differing in cellular origin, numbers, size, antigenic composition and functional properties. MP support coagulation by exposure of tissue factor (TF), the initiator of coagulation in vivo. Moreover, MP may transfer bioactive molecules to other cells, thereby stimulating them to produce cytokines, cell-adhesion molecules, growth factors and TF, and modulate endothelial functions. However, a comprehensive characterization of the antigenic composition of MP has been poorly defined. This study describes the protein composition of endothelial cell (EC)-derived MP (EMP) using a proteomic approach. MS analysis indicated the presence of newly described protein such as metabolic enzymes, proteins involved in adhesion and fusion processes, members of protein folding event, cytoskeleton associated proteins and nucleosome. In conclusion, circulating EMP behave as an actual storage pool, able to disseminate blood-borne TF activity and other bioactive effectors, as confirmed by our experiments showing an increased procoagulant activity of EC exposed to EMP.

Heritable factors shape natural human IgM reactivity to Ro60/SS-A and may predispose for SLE-associated IgG anti-Ro and anti-La autoantibody production

Systemic lupus erythematosus (SLE) is characterized by various IgG autoreactivities, among which anti-Ro/SS-A is particularly pathology-associated and early detectable. SLE also shows significant familial aggregation, but genetic factors are not well understood and remain controversial for disease-associated IgG. Here we report that IgM anti-Ro showed a uniquely high degree of heritability in a study of SLE-affected families. Unlike IgM anti-La or anti-dsDNA, IgM anti-Ro was also significantly correlated to IgG anti-Ro among SLE patients, as well as to IgG anti-La and anti-dsDNA. We conclude that largely genetically determined, thus natural IgM anti-Ro-bearing precursor B-cells, may be an important factor for class switching and determinant spreading in early phases of SLE pathogenesis. Furthermore, we found unexpected sex differences in isotype/specificity correlations among SLE-unaffected relatives and control subjects, which could help understand the strong gender bias associated with SLE. We propose that the study of such correlation structures may reveal characteristic spreading pathways relevant for human SLE.

Quantitative determination of the binding of beta2-glycoprotein I and prothrombin to phosphatidylserine-exposing blood platelets

The plasma protein beta2GPI (beta2-glycoprotein I) has been proposed to mediate phagocytosis of apoptotic cells and to play a role in the antiphospholipid syndrome. This suggestion is based mainly on the presumption that beta2GPI has an appreciable interaction with PS (phosphatidylserine)-exposing cell membranes. However, quantitative data on the binding of beta2GPI to PS-exposing cells under physiologically relevant conditions are scarce and conflicting. Therefore we evaluated the binding of beta2GPI to PS-expressing blood platelets. Flow cytometry showed that binding of beta2GPI is negligible at physiological ionic strength, in contrast with significant binding occurring at low ionic strength. Binding parameters of beta2GPI and (for comparison) prothrombin were quantified by ellipsometric measurement of protein depletion from the supernatant following incubation with platelets. At low ionic strength (20 mM NaCl, no CaCl2), a dissociation constant (K(d)) of 0.2 microM was found for beta2GPI, with 7.4x10(5) binding sites per platelet. Under physiologically relevant conditions (120 mM NaCl and 3 mM CaCl2), binding of beta2GPI was not detectable (extrapolated K(d)>80 microM). Prothrombin binding (at 3 mM CaCl2) was much less affected by ionic strength: K(d) values of 0.5 and 1.4 muM were observed at 20 and 120 mM NaCl respectively. The low affinity and the presence of many lipid-binding proteins in plasma that can compete with the binding of beta2GPI suggest that only a small fraction (<5%) of the binding sites on PS-exposing blood cells are likely to be occupied by beta2GPI. These findings are discussed in relation to the alleged (patho-)physiological functions of beta2GPI.

In vitro procoagulant activity induced in endothelial cells by chemotherapy and antiangiogenic drug combinations: modulation by lower-dose chemotherapy

One of the emerging problems concerning the use of antiangiogenic drugs, when used in combination with certain chemotherapy regimens, is enhanced rates and severity of adverse clotting events. For as yet unknown reasons, certain drugs and particular combinations can induce an elevated incidence of thromboembolic events in treated cancer patients [e.g., SU5416, a vascular endothelial cell growth factor receptor-2 (VEGFR-2) antagonist, when combined with gemcitabine and cisplatin (CDDP)]. Such results highlight the need to develop assays capturing the essence of enhanced clot formation under such combination treatment and which may have predictive potential as well. Here, we report the possibility of such an assay (i.e., the ratio of tissue factor over tissue factor pathway inhibitor expression or activity in cultured human endothelial cells calculated as a coagulation index). A marked increase in coagulation index was observed after exposure to SU5416 and the CDDP/gemcitabine chemotherapy combination in contrast to either of these treatments used alone. Substitution of SU5416 with any one of ZD6474, SU6668, IMC-1121, a monoclonal antibody to VEGFR-2, or an antibody to VEGF (bevacizumab) did not cause a marked increase in the coagulation index, nor did the combination of SU5416 with 5-fluorouracil and leucovorin. Finally, we noted that reducing the concentrations of gemcitabine and CDDP (i.e., use of "metronomic dosing" in vitro) significantly attenuated the coagulation index increase induced by these drugs, suggesting that use of low-dose chemotherapy regimens might be an approach to consider for reducing the incidence of adverse clotting events associated with chemotherapy alone or in conjunction with antiangiogenic drug combination therapies.

Ultrastructural changes in endothelium during apoptosis indicate low microembolic potential

BACKGROUND

Apoptotic endothelium has been suggested to have microthrombotic and microembolic potential. While some describe pro-coagulant activities and platelet binding, others demonstrate maintained fibrinolytic protein and anti-platelet aggregatory activity. Canalicular fragmentation is unique to apoptotic endothelium and is suggested to facilitate size reduction of apoptotic cells to reduce microembolic potential. Despite the potential importance of apoptotic microemboli, there are no reports characterizing changes in cell size and shape during endothelial apoptosis.

METHODS

Here, we describe transmission and scanning electron microscopic studies of apoptotic endothelium and compare changes seen with apoptotic HL-60 cells incapable of canalicular fragmentation.

RESULTS

We demonstrate reduced endothelial size (p<0.05) with progressive apoptosis relative to apoptotic HL-60 cells. Mechanical stress accelerated size reduction of apoptotic endothelium(P< 0.01) but did not affect the size of apoptotic HL-60 cells. Mechanical stress also increased circularity in apoptotic endothelium (p<0.01), suggested to facilitate passage through small vessels. Earlier work indicated that canaliculi form through plasma membrane invagination, but we report fusion of small vesicles contributing to canalicular growth, while canaliculi fuse to form large vacuoles and also dilate at late stages of apoptosis.

CONCLUSIONS

These observations are consistent with the suggestion that endothelium is adapted to minimize microembolic potential and that canalicular fragmentation contributes to this.

Effect of mifepristone on proliferation and apoptosis of Ishikawa endometrial adenocarcinoma cells

OBJECTIVE

To determine the mechanism by which mifepristone improves breakthrough bleeding, the effects of mifepristone on proliferation and apoptosis of Ishikawa endometrial carcinoma cells were evaluated in the presence and absence of progestin.

DESIGN

Prospective basic research study.

SETTING

Research laboratories for reproductive health at a university medical school.

PATIENT(S)

None.

INTERVENTION(S)

Ishikawa cells were cultured in vitro. Mifepristone and/or medroxyprogesterone acetate at various concentrations were added to the cells.

MAIN OUTCOME MEASURE(S)

Determination of cell proliferation and apoptosis.

RESULT(S)

Colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and bromodeoxyuridine (BrdU) labeling analysis demonstrated that mifepristone inhibited the growth of Ishikawa cells and percentage of BrdU-labeled cells in a time- and dose-dependent manner. Flow cytometry analysis demonstrated that mifepristone at 100 micromol/L, which completely inhibited cell proliferation, increased the proportion of cells in the S phase and diminished the cells in the G2/M phase. Apoptosis was identified by annexin-V-fluorescein isothiocyanate binding and caspase-3 activation. Immunofluorescent double labeling of Ishikawa cells in the absence or presence of mifepristone revealed that BAX protein expression increased and translocated from cytosol to mitochondria.

CONCLUSION(S)

Mifepristone inhibited cell growth by arresting cell cycle progression at S phase, induced apoptosis through caspase-3 activation, and modulated apoptosis regulatory genes BCL2/BAX and FAS/FASLG in Ishikawa cells. Together, these data imply that the improvement in breakthrough bleeding observed with mifepristone might be due to diminished volume of endometrial tissue similar to that seen with endometrial atrophy.

Direct cleavage of ROCK II by granzyme B induces target cell membrane blebbing in a caspase-independent manner

Caspase activation in target cells is a major function of granzyme B (grB) during cytotoxic lymphocyte granule-induced apoptosis. grB-mediated cell death can occur in the absence of active caspases, and the molecular targets responsible for this additional pathway remain poorly defined. Apoptotic plasma membrane blebbing is caspase independent during granule exocytosis–mediated cell death, whereas in other instances, this event is a consequence of the cleavage by caspases of the Rho effector, Rho-associated coiled coil–containing protein kinase (ROCK) I. We show here that grB directly cleaves ROCK II, a ROCK family member encoded by a separate gene and closely related to ROCK I, and this causes constitutive kinase activity and bleb formation. For the first time, two proteins of the same family are found to be specifically cleaved by either a caspase or grB, thus defining two independent pathways with similar phenotypic consequences in the cells. During granule-induced cell death, ROCK II cleavage by grB would overcome, for this apoptotic feature, the consequences of deficient caspase activation that may occur in virus-infected or malignant target cells.

Overexpression of MMP9 and Tissue Factor in Unstable Carotid Plaques Associated with Chlamydia pneumoniae, Inflammation, and Apoptosis

Tissue remodeling by matrix metalloproteinases (MMPs) and plasminogen activators such as tissue factor (TF) is postulated to be involved in the pathogenesis of atherosclerosis. The in situ expression of MMP9 and TF in unstable atherosclerotic plaques has not been examined in detail. Moreover, interference of tissue remodeling by vascular inflammation, apoptosis, and Chlamydia pneumoniae inside plaque subregions is unclear. A total of 40 autopsy carotid arteries (controls) and 20 atherosclerotic carotid endarterectomy specimens (with type VI lesions, according to the American Heart Association classification) from stroke patients were analyzed for expression of MMP9 and TF using in situ techniques. The data on tissue remodeling were correlated with the presence of inflammatory cells (T cells, B-cells, macrophages), apoptosis, and the presence of C. pneumoniae using immunohistochemistry and Western blot analyses. We found a significant overexpression of MMP9 and TF in progressive atherosclerotic carotid arteries, especially in the shoulder and cap subregions (both p < 0.05). Expression of MMP9 and TF correlated significantly with T-cell and macrophage infiltrates as well as with apoptosis (p < 0.05). C. pneumoniae infection was significantly associated with elevated TF expression (p < 0.01) but not with MMP9. MMP9 and TF are thus significantly overexpressed in progressive atherosclerotic plaques, and their relevant subregions (shoulder and cap) are involved in plaque instability. This process is associated with local inflammatory cell infiltrates and apoptosis, which might be influenced by infectious agents such as C. pneumoniae.

Anti-phospholipid antibodies (aPL) and apoptosis: prothrombin-dependent aPL as a paradigm for phospholipid-dependent interactions with apoptotic cells

The natural targets of anti-phospholipid antibodies (aPL) and the stimuli that induce them remain unknown. Apoptotic cells have been proposed as both potential targets and immunogens for anti-phospholipid antibodies. Demonstration of selective recognition by anti-phospholipid antibodies provides support for apoptotic cells as antigenic targets. Here, we summarize data showing that prothrombin (PT) binds to apoptotic, but not viable, cells, and that apoptotic-cell bound prothrombin provides a target for human polyclonal and murine monoclonal lupus anticoagulant (LA) antibodies. We discuss findings for two monoclonal lupus anticoagulant antibodies that have high (antibody 29J3-62) or low (antibody 29I4-24) affinity, respectively, for soluble prothrombin. Despite their very different affinities for soluble prothrombin, both monoclonal antibodies reacted similarly with prothrombin bound to phospholipid or apoptotic cells. Furthermore, both antibodies enhanced the binding of prothrombin to apoptotic cells. We propose that the recognition of apoptotic cells by these prothrombin-dependent monoclonal antibodies provides a paradigm for other anti-phospholipid autoantibodies. 29I4-24 is prototypical of phospholipid-dependent anti-phospholipid antibodies, while 29J3-62 represents a prototype for phospholipid-independent anti-phospholipid antibodies. Proteins such as prothrombin and beta2-glycoprotein I (beta2GPI) bind to apoptotic cells, thereby enhancing the recognition of apoptotic cells by anti-phospholipid antibodies. Furthermore, anti-phospholipid antibodies potentiate the interaction of these proteins with apoptotic cells. While it is unclear whether apoptotic cells are the inducing stimuli in patients with anti-phospholipid antibodies or even whether anti-phospholipid antibodies interact with apoptotic cells in vivo, it is nonetheless clear that anti-phospholipid antibodies have the potential to affect both the procoagulant activity and the uptake and clearance of apoptotic cells.

Generation of novel covalent RNA-protein complexes in cells by ultraviolet B irradiation: implications for autoimmunity

OBJECTIVE

To determine whether ultraviolet B (UVB) irradiation induces novel modifications in autoantigens targeted during experimental photoinduced epidermal damage.

METHODS

To search for novel UVB-induced autoantigen modifications, lysates made from UVB-irradiated human keratinocytes or HeLa cells were immunoblotted using human autoantibodies that recognize ribonucleoprotein autoantigens. Novel autoantigen structures identified were further characterized using nucleases and RNA hybridization.

RESULTS

Human sera that recognize U1-70 kd (U1-70K) and La by immunoblotting also recognized multiple novel species when they were used to immunoblot lysates of UVB-irradiated keratinocytes or HeLa cells. These species were not present in control cells and were not observed when apoptosis was induced by Fas ligation or cytotoxic lymphocyte granule contents. Biochemical analysis using multiple assays revealed that these novel UVB-induced molecular species result from the covalent crosslinking between the U1 RNA and the hYRNA molecules with their associated proteins, including U1-70K, La, and likely components of the Sm particle.

CONCLUSION

These data demonstrate that UVB irradiation of live cells can directly induce covalent RNA-protein complexes, which are recognized by human autoantibodies. As previously described for other autoantigens, these covalent complexes of RNA and proteins may have important consequences in terms of antigen capture and processing.

Budding, vesiculation and permeabilization of phospholipid membranes—evidence for a feasible physiologic role of β2-glycoprotein I and pathogenic actions of anti-β2-glycoprotein I antibodies

The in vivo physiologic role of beta2-glycoprotein I (beta2GPI) is presumed to be related to its interactions with negatively charged phospholipid membranes. Increased quantities of procoagulant microparticles derived by the vesiculation of blood cells have been detected in patients with antiphospholipid syndrome (APS) frequently associated with antibodies against beta2GPI (anti-beta2GPI). We investigated the influence of beta2GPI and anti-beta2GPI on giant phospholipid vesicles (GPVs). GPVs composed of phosphatidylserine and phosphatidylcholine were formed in an aqueous medium and individually transferred to a compartment containing either beta2GPI, anti-beta2GPI, or beta2GPI along with anti-beta2GPI. Shape changes of a single GPV were observed by a phase contrast microscope. Most GPVs transferred to the solution containing only beta2GPI budded moderately. Upon the transfer of GPVs to the solution containing beta2GPI and anti-beta2GPI either from patient with APS or mouse monoclonal anti-beta2GPI Cof-22, the budding was much more pronounced, generating also daughter vesicles. No such effects were seen when GPV was transferred to the solution containing anti-beta2GPI without beta2GPI. Our results suggest a significant physiologic role of beta2GPI in the budding of phospholipid membranes, which may be explained by the insertion of the C-terminal loop of beta2GPI into membranes, thus increasing the surface of the outer layer of a phospholipid bilayer. Anti-beta2GPI, recognizing domains I to IV of beta2GPI, enhanced the budding and vesiculation of GPVs in the presence of beta2GPI. This might be a novel pathogenic mechanism of anti-beta2GPI, promoting in vivo the expression of proadhesive and procoagulant phospholipid surfaces in APS.

Antibodies against granulosa luteinized cells and their targets in women attending IVF program

PROBLEM

The study was conducted to investigate the presence and the possible role of anti-granulosa luteinized cells (GLCs) antibodies in infertile patients, attending in vitro fertilization (IVF) cycles, as well as to attempt the identification of putative target antigens.

METHOD OF STUDY

A total of 101 sera from infertile women (patient group) and 33 sera from fertile women (control group) were investigated. The patients were divided in subgroups according to: ovarian response to controlled ovarian hyperstimulation (COHS)--poor responders and good responders; fertilization rate--low fertilization rate and high fertilization rate. The relation between embryo transfer (ET) outcome and prevalence of anti-GLC antibodies was investigated too. NONIDET P-40 (NP-40) and whole-GLC lysates, as antigenic materials, were used in enzyme-linked immunosorbent assay (ELISA) and immunoblotting, respectively.

RESULTS

Based on the cut-off value of 2 S.D. above the control mean value, the prevalence of patients positive for anti-GLC antibodies was found to be 28.7% (29/101) compared with 9.1% (3/33) in control fertile women (P < 0.05). Anti-GLC antibodies were detected in 54.8% (17/31) of women with low fertilization rate compared with 15.7% (11/70) of women with high fertilization rate (P = 0.003) and it was established that women positive for anti-GLC antibodies had lower fertilization rate, than those negative for anti-GLC antibodies. Immunoblotting has demonstrated a number of GLC proteins with molecular masses (MM) of 110, 70-80, 47 and 37 kDa, frequently reacting with anti-GLC antibodies in patient's sera, as possible targets.

CONCLUSION

The presented results on the prevalence and role of anti-GLC antibodies, as well as the data on the target antigens confirmed our hypothesis about the potential involvement of GLC antigens in some cases of immunological infertility in IVF patients.

Vessel wall apoptosis and atherosclerotic plaque instability

Atherosclerotic cardiovascular disease remains the leading cause of death in the industrialized world. Most cardiovascular deaths result from acute coronary syndromes, including unstable angina pectoris and acute myocardial infarction. Coronary syndromes often arise from acute coronary thrombosis, itself commonly a result of disruption or rupture of the fibrous cap of a lipid-laden atherosclerotic plaque. Despite this huge clinical burden of atherosclerotic plaque instability, our understanding of the molecular mechanisms mediating atherosclerotic plaque disruption and rupture, at a cellular level, remains limited. Placed in a clinical context, this review discusses our current understanding of the molecular basis for atherosclerotic plaque instability, with particular emphasis on the process of apoptosis-or programmed cell death-seen increasingly as playing a key role in a number of cell types within the vessel wall.

Na+ influx triggers bleb formation on inner hair cells

Large blebs form rapidly on apical membranes of sensory inner hair cells (IHCs) when the organ of Corti is freshly isolated from adult guinea pigs. Bleb formation had two distinguishable phases. Initially, we identified small particles labeled with fluorescent annexin V; these rapidly coalesced into larger aggregates. After particle aggregation, a single membrane bleb emerged from cuticular plate at the vestigial kinocilium location, eventually reaching approximately 10 microm maximum spherical diameter; blebs this size often detached from IHCs. Development of blebs was associated with elevated concentration of intracellular Na(+); blocking Na(+) influx through mechanotransduction and ATP channels in the apical pole of IHCs or by replacement of Na(+) with N-methyl-D-glucamine prevented Na(+) loading and bleb formation. Depletion of intracellular ATP, blocking cAMP synthesis, inhibition of vesicular transport with brefeldin A, or inhibition of phosphatidylinositol 3-kinase with 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one (LY-294002) significantly reduced bleb formation in the presence of a Na(+) load. Neither the mechanism of blebbing nor the size growth of the IHC blebs was associated with cellular apoptosis or necrosis. Bleb formation was not significantly reduced by disassembling microtubules or decreasing intracellular hydrostatic pressure. Moreover, no polymerized actin was observed in the lumen of blebs. We conclude that IHC bleb formation differs from classic blebbing mechanisms and that IHC blebs arise from imbalance of endocytosis and exocytosis in the apical plasma membrane, linked to Na(+) loading that occurs in vitro.

Annexin A5 down-regulates surface expression of tissue factor: a novel mechanism of regulating the membrane receptor repertoir

Phosphatidylserine (PtdSer) is exposed on the external leaflet of the plasma membrane during apoptosis. The protein annexin A5 (anxA5) shows high affinity for PtdSer. When anxA5 binds to the PtdSer-expressing membranes during apoptosis, it crystallizes as an extended two-dimensional network and activates thereby a novel portal of cell entry that results in the internalization of the PtdSer-expressing membrane patches. This novel pathway of cell entry is potentially involved in the regulation of the surface expression of membrane receptors. In this study we report the regulation of surface expression of the initiator of blood coagulation tissue factor (TF) by this novel pathway of cell entry. AnxA5 induces the internalization of tissue factor expressed on the surface of apoptotic THP-1 macrophages. This down-regulation depends on the abilities of anxA5 to bind to PtdSer and to form a two-dimensional crystal at the membrane. We furthermore show that THP-1 cells produce and externalize anxA5 that cause the internalization of TF in an autocrine type of mechanism. We extended our in vitro work to the in vivo situation and show in a mouse model that anxA5 causes the down-regulation of TF expression by smooth muscle cells of the media of the carotid artery that was mechanically injured. In conclusion, anxA5 down-regulates surface-expressed TF by activating the novel portal of cell entry. This mechanism may be part of a more general autocrine function of anxA5 to regulate the plasma membrane receptor repertoir under stress conditions associated with the surface expression of PtdSer.

Apoptosis and estrogen deficiency in primary Sjögren syndrome

PURPOSE OF REVIEW

Primary Sjögren syndrome is an autoimmune disorder characterized by lymphocytic infiltrates and destruction of the salivary and lacrimal glands, and systemic production of autoantibodies to the ribonucleoprotein particles SS-A/Ro and SS-B/La. The purpose of this review is to discuss recent advances in the pathogenesis of primary Sjögren syndrome.

RECENT FINDINGS

Although several candidate autoantigens including alpha-fodrin have been reported in Sjögren syndrome, the pathogenic roles of the autoantigens in initiation and progression of SS are still unclear. It is possible that individual T cells activated by an appropriate self antigen can proliferate and form a restricted clone. Recent evidence suggests that the apoptotic pathway plays a central role in tolerizing T cells to tissue-specific self antigen, and may drive the autoimmune phenomenon. Cleavage of certain autoantigens during apoptosis may reveal immunocryptic epitopes that could potentially induce autoimmune response. The studies reviewed imply that Fas-mediated cytotoxicity and caspase-mediated alpha-fodrin proteolysis are involved in the progression of tissue destruction in Sjögren syndrome. Fas ligand (FasL), and its receptor Fas are essential in the homeostasis of the peripheral immune system. It can be considered that a defect in activation-induced cell death of effector T cells may result in the development of autoimmune exocrinopathy in Sjögren syndrome.

SUMMARY

Although the mechanisms by which estrogen deficiency influences autoimmune lesions remain unclear, it is possible that antiestrogenic actions might be a potent factor in the formation of pathogenic autoantigens.

The role of FcgammaRIIA and IIIA polymorphisms in autoimmune diseases

Our knowledge about the role of human Fc receptors for IgG (FcgammaR) has increased considerably within the last several years. These receptors vary in their affinity for IgG, their preferences for IgG subclasses, the cell type-specific expression patterns, and the intracellular signals that they elicit. Additional FcgammaR heterogeneity is introduced by the presence of well characterized genetic polymorphisms. Allelic variants of FcgammaR genes may influence phagocyte biologic activity, providing a basis for inherited predisposition to disease. Recent evidence suggests that certain FcgammaR alleles are genetic risk factors for systemic autoimmune diseases and the development of major manifestations of these diseases. The FcgammaRIIA-R/H131 polymorphism is an important determinant of predisposition to systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). FcgammaRIIA-R131, the low-binding IgG2 allele, seems to confer risk for APS under a recessive model, whereas its effect on SLE susceptibility probably has a dose-response character. The population-attributable fraction of lupus cases due to the R131 allele is 13% and for APS cases is at least 10%, in subjects of European descent. The FcgammaRIIIA-V/F158 polymorphism has a significant impact on renal involvement in lupus patients. The proportion of nephritis cases that could be attributed to the low-binding IgG1 and IgG3 F158 allele is approximately 10-14%. These genetic associations have been well documented in meta-analyses including a large number of studies. Besides the epidemiologic and pathophysiologic interest, this knowledge may be of use in the future in designing novel therapeutic interventions.

Anti-beta 2 glycoprotein I antibodies in centenarians

BACKGROUND

Non-organ-specific autoantibodies are present in centenarians without evidence of autoimmune diseases but conflicting or no data on anti-phospholipid and anti-phospholipid binding proteins were reported.

OBJECTIVE

To investigate the presence and antigen specificity of anti-phospholipid and anti-phospholipid binding proteins in centenarians.

METHODS

Seventy-seven centenarians, 70 adult controls, 65 unselected elderly subjects, and 38 old SENIEUR volunteers were investigated. Anti-cardiolipin, anti-human beta 2 glycoprotein I, and lupus anticoagulant were detected. Antigen specificity was assayed against plates coated with anionic, neutral and cationic phospholipids and beta 2 glycoprotein I-dependence was also evaluated.

RESULTS

54.3% of the centenarians were positive for IgG and 8.6% for IgM anti-beta 2 glycoprotein I antibodies, while only 20.7% centenarians were positive for anti-cardiolipin IgG and 2.59% for IgM; none resulted positive for lupus anticoagulant. Anti-cardiolipin positive sera cross-reacted with negatively charged phospholipids and displayed decreased binding to serum-free cardiolipin-coated plates that was restored by human beta 2 glycoprotein I or fetal calf serum.

CONCLUSIONS

Centenarians display high reactivity against human beta 2 glycoprotein I but low binding to the bovine molecule in the anti-cardiolipin assay. In spite of the presence of antibodies comparable to those found in patients with the anti-phospholipid syndrome, no vascular events were reported suggesting the presence of unknown protective factors and/or the lack of triggering factors.

ING4 induces G2/M cell cycle arrest and enhances the chemosensitivity to DNA-damage agents in HepG2 cells

The known members of inhibitor of growth (ING) gene family are considered as candidate tumor suppressor genes. ING4, a novel member of ING family, is recently reported to interact with tumor suppressor p53, p300 (a major component of histone acetyl transferase complexes), and p65(RelA) subunit of NF-kappaB. In this study, we investigated the cellular behaviors of HepG2 cells with exogenous ING4. Interestingly, the overexpression of ING4 negatively regulated the cell growth with significant G2/M arrest of cell cycle, and moreover, enhanced the cell apoptosis triggered by serum starvation in HepG2 cells. Furthermore, the exogenous ING4 could upregulate endogenous p21 and Bax in HepG2 cells, not in p53-deficient Saos-2 cells, suggesting that G2/M arrest induced by ING4 could be mediated by the increased p21 expression in a p53-dependent manner, although there is no significant increase of p53 expression in HepG2 cells. Moreover, HepG2 cells with exogenous ING4 could significantly increase cell death, as exposed to some DNA-damage agents, such as etoposide and doxorubicin, implying that ING4 could enhance chemosensitivity to certain DNA-damage agents in HepG2 cells.

Validation of a novel tissue factor assay in experimental human endotoxemia

BACKGROUND

Nuclear factor kappa B (NF-kappa B) activation and tissue factor (TF) expression may contribute to lethality in sepsis. Inappropriate in vivo expression of TF is likely responsible for fibrin deposition in sepsis-associated disseminated intravascular coagulation (DIC). Clinical assessment of TF expression has remained a major challenge. No point-of-care assays are currently available to measure the level of TF activity in whole blood. The current study examined the suitability of the TiFaCT assay as a point-of-care assay to detect TF expression.

METHODS

30 healthy male volunteers received 2 ng/kg of LPS. Tissue factor-dependent coagulation was quantified with a novel assay called tissue factor clotting time (TiFaCT), and by measurement of activation markers of downstream coagulation.

RESULTS

Ex vivo addition of anti-TF antibodies to blood slightly increased clotting times at 0-24 h (p<0.01) indicating that some tissue factor activity was present in whole blood at any time. LPS bolus infusion decreased TiFaCT clotting time by -23% compared to baseline (p<0.01), when in vivo clotting increased, as demonstrated by a 10-fold increase in prothrombin fragment levels (F1+2). Ex vivo incubation with LPS considerably shortened TiFaCT (from 1000s to 400s as compared to control incubation; p<0.01). This effect was blunted at 2-4 h after LPS infusion (i.e. the time of monocytopenia), but twofold enhanced 24 h after LPS challenge (p<0.01).

CONCLUSIONS

In summary, the TiFaCT assay was validated in our in vivo model of LPS-induced coagulation. It detected minute quantities of circulating TF even at baseline. TiFaCT is shortened at times of in vivo thrombin generation.

Nucleosomes in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by the development of a large array of autoantibodies that primarily are directed against the whole chromatin (antinucleosome) and its individual components, dsDNA and histones. Apoptotic defects and impaired removal of apoptotic cells could contribute to an overload of autoantigens (and in particular of nucleosomes) in circulation or in target tissues that could become available to initiate an autoimmune response. In susceptible individuals, this can lead to autoantibody-mediated tissue damage. In addition to intrinsic or secondary apoptosis/apoptotic cell removal defects, certain apoptotic stimuli (eg, UV, viruses) could lead to posttranscriptional modifications that generate autoantigen cryptic fragments for which cells of the immune system have not been tolerized. Besides their role as a major immunogen in lupus, nucleosomes participate in antibody-mediated renal pathogenicity and act as a bridging molecule that recognizes heparin sulfate/collagen V components of the glomerular basement membrane. New tools that were developed to detect antinucleosome antibodies in the serum of patients (by ELISA) have shown the specificity and the high sensitivity of antinucleosome antibody reactivity in SLE. In particular, antinucleosome could be a useful marker of patients who have SLE and lack anti-dsDNA antibodies, a prognosis marker for imminent relapse, and a diagnosis marker of lupus nephritis.

Distinct maturation of, but not migration between, human monocyte-derived dendritic cells upon ingestion of apoptotic cells of early or late phases

Cell death via apoptosis is a normal physiological process. Rapid, but silent, removal of apoptotic cells (ACs) plays an essential role in maintaining homeostasis in the immune system. Defective clearance of ACs allows ACs to accumulate and undergo late phase apoptosis, also known as secondary necrosis, which may generate danger signals, leading to inflammation or autoimmunity. In this study we investigate the outcome of dendritic cells (DCs), which are potent APCs, on the interaction with ACs of early or late phase. Immature DCs internalized ACs of both early and late phases with similar efficiency. However, DCs that had taken up ACs of early phase acquired a non-fully mature DC phenotype, expressing low MHC class II complex, costimulatory molecule CD40, and mature DC-restricted marker CD83, and had a low capacity to stimulate allogeneic CD4+ T cell proliferation, whereas DCs that had taken up ACs of late phase acquired a mature DC phenotype with enhanced T cell stimulatory capacity. Ingestion of either early or late ACs induced minimal production of IL-12 and modulated CC chemokine and CCR expression in DCs. In particular, there was down-regulation of CCR5 and up-regulation of CCR7, resulting in switches in responsiveness from inflammatory to lymphoid chemokines. We conclude from these data that after taking up ACs of either early or late phases, DCs acquire the capability of homing to draining lymph nodes, and the distinct maturation between DCs taking up early or late ACs may contribute to DC function in the induction of T cell tolerance or Ag-specific T cell response, respectively.

Requirement of dying cells and environmental adjuvants for the induction of autoimmunity

OBJECTIVE

Cells commonly die without eliciting autoimmunity. However, dying cells are a potential initiating stimulus for systemic lupus erythematosus (SLE). Our goal was to verify whether immune adjuvants influence the autoimmunity induction that ensues following in vivo injection of dying cells.

METHODS

Mice were immunized with apoptotic thymocytes in the presence of artificial moieties, such as Freund's incomplete adjuvant (IFA), or natural adjuvants, such as dendritic cells (DCs). Renal involvement and the development of autoantibodies were monitored.

RESULTS

Apoptotic cells failed to induce clinical disease or to sustain production of autoantibodies in (NZB x NZW)F(1) mice. In contrast, autoimmunity developed in the presence of IFA or DCs. The characteristics of the adjuvant influenced the array of autoantibodies, the kinetics of their development, and the severity of the disease. DCs were required for induction of anti-beta(2)-glycoprotein I IgG. Adjuvants alone did not elicit disease.

CONCLUSION

A "two-hit" signal composed of autoantigens and adjuvants initiates systemic autoimmunity. Moreover, environmental signals at the site of clearance of dead cells shape the features and the severity of the autoimmune disease. Strategies aimed at preventing the accumulation of dying cells and at modulating endogenous adjuvants may be beneficial for the treatment of SLE.

Caspase-3 and Tissue Factor Expression in Lipid-Rich Plaque Macrophages

BACKGROUND

Macrophages associated with arterial wall lipid deposition contribute to inflammatory processes. Tissue factor (TF) has been implicated in the thrombogenicity of atherosclerotic plaques. Intimal cells undergoing apoptosis have been postulated as a source for TF. However, there is only limited knowledge of cell type, plaque component, and conditions associated with TF expression and apoptosis. We examined the hypothesis that macrophages exposed to conditions of lipid-rich plaque undergo apoptosis and express TF.

METHODS AND RESULTS

In human carotid (n=15) and coronary (n=6) atherosclerotic plaques, TF and caspase-3 mRNA and protein expression (evaluated by in situ hybridization and immunohistochemistry) were increased significantly in lipid-rich compared with fibrous plaque components (P<0.01) and correlated with high macrophage content (P<0.05). Double-labeling studies demonstrated colocalization of TF and active caspase-3. In hyperlipidemic mice, expression of TF and active caspase-3 was observed simultaneously and colocalized in neointimal macrophages after arterial injury. In neointima of normolipidemic animals, TF and active caspase-3 were absent after arterial injury. In monocytes cultured in the presence of oxidized LDL, strong induction and colocalization of TF and active caspase-3 were found compared with baseline (P<0.05). Both antigens were significantly decreased after cotreatment with a caspase inhibitor (P<0.05) and were absent in untreated control cells.

CONCLUSIONS

The expression of TF as the primary cell-associated activator of the coagulation pathway proves to be closely related to macrophages undergoing apoptosis in conditions of lipid-rich plaque, pointing to a key role of lipid content and inflammatory cell viability in determining plaque thrombogenicity.

Plasma membrane alterations during apoptosis: role in corpse clearance

Apoptosis is a program of cellular self-destruction culminating in the clearance of cell corpses by neighboring macrophages. Studies in recent years have served to characterize a number of structural and molecular plasma membrane alterations that act in concert to mediate efficient engulfment of cell corpses. Hence, "eat me" signals, including the anionic phospholipid phosphatidylserine (PS) and its oxidized counterpart, PS-OX, as well as the PS-binding protein, annexin I, are exposed on the surface of effete cells and function to mediate engulfment by neighboring phagocytic cells. Plasma membrane blebbing (zeiosis), a common feature of the apoptotic program, provides a structural context for the exposition of recognition signals insofar as PS molecules aggregate on the surface of these membrane protrusions. Apoptotic cells also secrete chemotactic factors ("seek me" signals), such as the phospholipid lysophosphatidylcholine, that recruit phagocytes to the site of the apoptotic lesion. Taken together, these events serve to mediate the disposal of effete cells prior to their necrotic disintegration, thus preventing the inflammation and tissue scarring that would otherwise ensue.

Studies of murine systemic autoimmunity

Systemic autoimmunity is an important clinical problem, offering a window into fundamental questions of self-nonself tolerance. We have used cellular immunology, serology, and immunopathology to approach several spontaneous mouse models. Although much remains to be done, a picture is emerging of pathological antigen-driven immune responses to self nuclear antigens, highly dependent on multiple genes, and susceptible to abnormalities of apoptosis.

Calcium and Its Role in the Nuclear Translocation and Activation of Cytosolic Phospholipase A2in Cells Rendered Sensitive to TNF-Induced Apoptosis by Cycloheximide

In these experiments, we investigated the role of calcium as a second messenger in the apoptotic activation of cytosolic phospholipase A(2) (cPLA(2)). As our model, we used a murine fibroblast cell line (C3HA) that was induced to undergo apoptosis by a combination of TNF and cycloheximide. Using fura 2 Ca(2+) imaging, we found strong evidence for an intracellular calcium response after 1 h of treatment, which correlated with the onset of phosphatidylserine externalization, but preceded effector procaspase processing by several hours. The response was strongest in the perinuclear region, where mean levels rose 83% (144 +/- 14 nM in untreated cells vs 264 +/- 39 nM in treated), while cells displaying morphological evidence of apoptosis had the highest levels of calcium (250-1000 nM). Verapamil blocked this response, indicating an extracellular source for the calcium. Fluorescence microscopy revealed a pattern of nuclear translocation of cPLA(2) during apoptosis, which was also blocked by verapamil, indicating an important role for calcium in this process. In addition, we found that verapamil prevented the release of [(3)H]arachidonic acid from C3HA cells induced to undergo apoptosis by the chemotherapeutic agents vinblastine, melphalan, and cis-platinum. Together, these data suggest that calcium is important for cPLA(2) activation by diverse apoptotic stimuli.

Apoptosis and immune responses to self

The mystery that surrounds autoimmunity revolves around how the immune system of patients who have systemic autoimmune diseases becomes primed to recognize intracellular antigens, how the autoantibodies thus produced contribute to the pathogenesis of the disease, and how those autoantibodies access their target proteins. By examining the mechanisms that are involved in the normal cellular process of apoptosis, we are beginning to unravel this mystery. The intracellular autoantigen targets of many systemic autoimmune diseases become altered during apoptosis in ways that may change how they are perceived by the immune system. High concentrations of self-antigens, or in the case of viral infection, complexes of foreign and self-antigens, are packaged during generation of apoptotic cells. The packages also may contain altered fragments of self-antigens that have not been encountered previously by the immune system. Under normal circumstances, apoptotic cells are cleared rapidly by macrophages and DCs. The normal consequence of that clearance is that the apoptosis-altered self-antigens are either ignored by the immune system or tolerance to those antigens is maintained. Clearance is achieved through complex mechanisms that enable macrophages and DCs to recognize apoptotic cells as nonthreatening "self" particles. Defects in this process that cause a delay in clearance could change the appearance of apoptotic cells and cause them to be recognized as "foreign invaders," thereby stimulating an inflammatory response that, in turn, activates an immune response to self-antigens. By studying the mechanisms that are involved in recognition and clearance of apoptotic cells, we are uncovering clues to the defects that may underlie the development of systemic autoimmunity.

Complement and immunity

Our body is in constant interaction with the environment. Some of the interactions involve the recognition and disposal of foreign substances that may harm the delicate balance between health and disease. The foreign elements, or antigens, include infectious organisms and lifeless macromolecules. The ability of the body to recognize what is dangerous and what is inconsequential, and to refrain from damaging what is perceived as self, are the main functions of the immune system. One important component of the innate immune response is the complement system. This article describes the different mechanisms of how complement is activated and the consequence of this activation, followed by a characterization of the complement's role in inflammation and autoimmunity, and the therapeutic considerations emanating from these studies.

Phagocytosis of apoptotic cells and the resolution of inflammation

Clearance of apoptotic cells by phagocytic cells plays a significant role in the resolution of inflammation, protecting tissue from harmful exposure to the inflammatory and immunogenic contents of dying cells. Apoptosis induces cell surface changes that are important for recognition and engulfment of cells by phagocytes. These changes include alterations in surface sugars, externalization of phosphatidylserine and qualitative changes in the adhesion molecule ICAM-3. Several studies have contributed to clarify the role of the receptors on the surface of phagocytes that are involved in apoptotic cell clearance. The phagocytic removal of apoptotic cells does not elicit pro-inflammatory responses; in contrast, apoptotic cell engulfment appears to activate signals that suppress release of pro-inflammatory cytokines. Therefore, clearance of apoptotic leucocytes is implicated in the resolution of inflammation and mounting evidence suggests that defective clearance of apoptotic cells contributes to inflammatory and autoimmune diseases. Defining the ligands on apoptotic cells and the corresponding receptors on phagocytes with which they engage, is likely to lead to the development of novel anti-inflammatory pro-resolution drugs. In this article, we will review the recognition and signaling mechanisms involved in the phagocytosis of apoptotic cells as well as the role of endogenous compounds that play a relevant role in the modulation of inflammation. We will also discuss what is currently known about diseases that may reflect impaired phagocytosis and the consequences on inflammation and immune responses.

Somatic mutations to arginine residues affect the binding of human monoclonal antibodies to DNA, histones, SmD and Ro antigen

Autoantibodies to a wide variety of antigens are associated with systemic lupus erythematosus (SLE). Antibodies to double-stranded DNA (anti-dsDNA) are thought to be particularly closely related to tissue damage and disease activity in SLE. Autoantibodies to histones, Sm and Ro are found in patients with SLE, but their role in pathogenesis is unclear. Using a transient expression system, we previously showed that particular sequence motifs in CDRs of light chains derived from the human Vlambda gene 2a2 are very important in determining their ability to form a DNA-binding site, when paired with the heavy chain of the human monoclonal anti-dsDNA antibody B3. These motifs are often sites of somatic mutation and/or contain arginine residues. In the experiments reported in this paper, the same expression system was used to show that these CDR motifs also affect binding to histones, Ro antigen and Sm antigen, but that binding to different antigens is affected in diverse ways by particular changes in the sequence of the CDRs. The heavy chain also plays a role in binding to these antigens. Pairing of the same range of 11 2a2 derived light chains with the heavy chain of a different anti-DNA antibody, 33.H11, gave reduced ability to bind DNA in comparison with the results obtained using the B3 heavy chain. Computer-generated models of the three-dimensional structures of these heavy/light chain combinations were used to define the positions occupied by the important sequence motifs at the binding sites of these antibodies, and to explain the different effects exerted by arginine residues at different positions in the light chains.

Impaired Clearance of Apoptotic Cells Induces the Activation of Autoreactive Anti-Sm Marginal Zone and B-1 B Cells

Since apoptotic cell Ags are thought to be a source of self-Ag in systemic lupus erythematosus, we have examined the role of apoptotic cells in the regulation and activation of B cells specific for Sm, a ribonucleoprotein targeted in human and murine lupus. Using Ig-transgenic mice that have a high frequency of anti-Sm B cells, we find that apoptotic cell injection induces a transient splenic B cell response, while simultaneously causing extensive splenic and peritoneal anti-Sm B cell death. In contrast, mice deficient in the clearance of apoptotic cells develop a chronic anti-Sm response beginning at 1-2 mo of age. These mice have expanded marginal zone and B-1 B cell populations and anti-Sm B cells of both types are activated to form Ab-secreting cells. This activation appears to be Ag-specific, suggesting that activation is due to increased availability of apoptotic cell Ags. Since marginal zone and B-1 cells are positively selected, these data suggest a loss of ignorance rather than a loss of tolerance.

Dendritic cells under investigation in autoimmune disease

Autoimmune disorders play an increasing role in public health, especially in light of the fact of the growing aged population, which primarily develop such diseases. A clear understanding of the mechanisms leading to the development of autoimmune responses and finally to autoimmune disease does not exist. Autoimmunity is characterized by the presence of autoantibodies and/or autoreactive T cells and the corresponding organ manifestation. Following the discovery of autoreactive T cells found in the periphery of mice and humans, the old immunological concept that autoreactive T cells are completely deleted in the thymus during evolution has been revised in recent years. Although antigen-presenting cells and particularly dendritic cells are known to play an important role in the regulation of immune responses and the activation of T cells, recent evidence suggests that the role of dendritic cells in the development of autoimmunity has been underestimated previously. This article aims to give a general overview on the basic immunological principles involved and gives a short review of the current literature on the functional relevance of dendritic cells in various human and murine autoimmune disorders.

Endothelium as a target for antiphospholipid antibodies

Several, and not necessarily alternative, pathogenic mechanisms have been suggested to sustain the thrombophilic diathesis of the anti-phospholipid syndrome. Among them, interference of anti-phospholipid antibodies with cell acting in the coagulation cascade likely plays a major role. Anti-phospholipid antibodies have been shown to react with endothelial cells mainly by reacting with beta 2 glycoprotein I expressed on the cell membrane surface. Beta 2 glycoprotein I can adhere to endothelial cell surface through the Annexin II receptor and through negatively charged structures (heparin-like molecules) that are bound by the phospholipid-binding site of the molecule. The autoantibody binding involves a yet unknown receptor that activates a signalling pathway able to translocate NFkappaB from the cytoplasm to the nucleus and to activate genes for adhesion molecule, pro-inflammatory cytokine and Tissue Factor up-regulation. The ultimate effect is the induction of a pro-inflammatory and a pro-coagulant endothelial phenotype that has been reproduced both in vitro and in vivo experimental models. Additional effects of anti-phospholipid-mediated endothelial cell activation are the interference with the protein C/S system, with the Annexin V binding, the up-regulation of endothelin I synthesis and the induction of apoptosis. Altogether these effects cooperate in switching endothelium from an anti-coagulant to a pro-coagulant surface.

Exposure of anionic phospholipids serves as anti-inflammatory and immunosuppressive signal--implications for antiphospholipid syndrome and systemic lupus erythematosus

In contrast to necrotic cells, the clearance of apoptotic ones usually is an anti-inflammatory process which elicits only a marginal immune response. During apoptosis phosphatidylserine (PS) is exposed on the outer leaflet of the cytoplasmic membrane and serves as target for the PS receptor of phagocytes. The latter is responsible for anti-inflammatory signalling and the induction of TGFbeta. We were interested whether the immunogenicity of apoptotic cells can be increased by masking PS. We observed that treatment of xenogeneic apoptotic cells with annexin V (AxV) significantly increased the humoral immune response against surface epitopes of these cells. Furthermore, AxV-coated irradiated tumour cells were able to elicit a long lasting tumour specific cytotoxic T lymphocyte response. AxV efficiently blocked the uptake of irradiated cells by macrophages but not by dendritic cells. Furthermore, AxV skewed the phagocytosis of irradiated cells towards inflammation. Investigation of patients with autoimmune diseases further supported the role of anionic surface phospholipids for anti-inflammatory clearance of apoptotic cells. Impaired clearance and opsonisation with anti-phospholipid-antibodies are discussed to be responsible for the development of systemic lupus erythematosus and anti-phospholipid-syndrome, respectively. Presentation of cryptic epitopes from late apoptotic cells in a proinflammatory context may challenge T cell tolerance. In addition, accumulation of uncleared apoptotic debris in the germinal centres of lymph nodes may result in the survival of autoreactive B cells.

Apoptosis in systemic lupus erythematosus

Systemic lupus erythematosus is a complex, multisystem autoimmune disease characterized by production of high-titer autoantibodies directed against ubiquitously expressed self-antigens. Autoantigens in systemic lupus erythematosus are highly diverse in terms of structure and location in control cells, but become clustered in and on the surface blebs of apoptotic cells. The past several years have provided significant evidence that the apoptotic cell plays a central role in tolerizing B cells and T cells to both tissue-specific and ubiquitously expressed self-antigens, and may drive the autoimmune response in systemic autoimmune disease. The authors review the significant recent advances in this area. Recent studies suggest that predisposing factors to subsequent development of systemic autoimmunity may be the incomplete induction of tolerance to apoptotic antigens, potentially through abnormal apoptotic signaling and effector pathways, decreased apoptotic cell clearance, or abnormal signaling thresholds on responding lymphocytes. In such genetically susceptible hosts, proinflammatory events at the host-environment-immune system interface that lead to the binary change in the response to apoptotic material from tolerance to immunity may be responsible for initiation of autoimmunity and subsequent disease amplification. Such pathways may be amenable to therapeutic and preventive interventions.

Role of the Fcgamma receptor IIA polymorphism in the antiphospholipid syndrome: an international meta-analysis

OBJECTIVE

To assess the impact of the FcgammaRIIA-R/H131 polymorphism on the risk for antiphospholipid syndrome (APS), both primary and secondary to systemic lupus erythematosus (SLE).

METHODS

This international meta-analysis combined data from 9 research teams. FcgammaRIIA-R/H131 genotypes were determined in 481 APS cases (206 with primary APS), 1,420 SLE controls, and 1,655 disease-free controls. Data were combined using fixed-effects and random-effects models.

RESULTS

Compared with disease-free controls, the RR genotype was enriched in the entire group of APS cases (odds ratio [OR] 1.65, 95% confidence interval [95% CI] 1.28-2.14); this was driven mostly by patients with secondary APS (OR 1.95, 95% CI 1.45-2.63). The excess of RR homozygotes but not heterozygotes among APS patients suggested a recessive mode of inheritance, rather than the additive model seen for SLE susceptibility, where RR conferred greatest risk, and RH intermediate risk, for SLE. This probably reflected the additional influence of another opposing genetic effect of HH homozygosity on APS predisposition (OR 0.72 for RH versus HH, 95% CI 0.55-0.96). Among SLE patients, those with APS were more frequently HH homozygotes than heterozygotes (OR 0.56 for RH versus HH, 95% CI 0.39-0.81). HH homozygosity also tended to predominate in primary APS compared with secondary APS (OR 0.50 for RR versus HH, 95% CI 0.25-0.99 by fixed-effects model). There was no significant between-study heterogeneity for any of these effects.

CONCLUSION

The FcgammaRIIA-R/H131 polymorphism is an important determinant of predisposition to APS, with different influences on SLE and APS susceptibility per se.

Cellular microparticles: what are they bad or good for?

Microparticles are fragments released from the plasma membrane of most stimulated or apoptotic cells. After having long been considered inert cell debris, of possible value for the diagnosis of cell activation or death, there is increasing documented evidence that they can interact with neighboring or remote cells, in which case they acquire a pathophysiologic potential. On the one hand, deleterious microparticles stemming from activated cells can elicit an adverse response from other cells, themselves undergoing membrane vesiculation, leading to pathogenic amplification. On the other hand, since they are thought to reflect a balance between cell stimulation, proliferation, and death, it is conceivable that they are discerned as sensors for the maintenance of homeostasis in multicellular organisms. Because vesiculation is an integral part of the plasma-membrane remodeling process, with the transverse migration of procoagulant phosphatidylserine from the cytoplasmic to the exoplasmic leaflet as the central event, the majority of released microparticles are thought to fulfill a hemostatic function under physiologic conditions. This is particularly true when they originate from platelets, with possible deviation towards thrombosis when produced in excess. Owing to these procoagulant properties, the hemostasis laboratory offers the most appropriate tools for the assessment of the in vivo significance of microparticles.

Aminophospholipid asymmetry: A matter of life and death

Maintenance of membrane lipid asymmetry is a dynamic process that influences many events over the lifespan of the cell. With few exceptions, most cells restrict the bulk of the aminophospholipids to the inner membrane leaflet by means of specific transporters. Working in concert with each other, these proteins correct for sporadic incursions of the aminophospholipids to the outer membrane leaflet as a result of bilayer imbalances created by various cellular events. A shift in the relative contribution in each of these activities can result in sustained exposure of the aminophospholipids at the cell surface, which allows capture of the cells by phagocytes before the integrity of the plasma membrane is compromised. The absence of an efficient recognition and elimination mechanism can result in uncontrolled and persistent presentation of self-antigens to the immune system, with development of autoimmune syndromes. To prevent this, phagocytes have developed a diverse array of distinct and redundant receptor systems that drive the postphagocytic events along pathways that facilitate cross-talk between the homeostatic and the immune systems. In this work, we review the basis for the proposed mechanism(s) by which apoptotic ligands appear on the target cell surface and the phagocyte receptors that recognize these moieties.

High levels of circulating endothelial microparticles in patients with acute coronary syndromes

BACKGROUND

Endothelial injury plays a critical role in coronary artery disease (CAD), but the assessment of this injury has been problematical. Recently, it has been shown in vitro that endothelial cells (ECs) release endothelial microparticles (EMPs) on activation or apoptosis and that an assay of EMPs can provide useful information on EC status in patients with thrombotic disorders. This study is aimed at assessing possible correlations between EMPs, which are markers of endothelial injury, and clinical subgroups of patients with CAD.

METHODS

A prospective, case-controlled study was conducted on 84 patients with CAD and 42 control subjects to investigate EMP profiles. Included were 64 patients with acute coronary syndromes ([ACS], 38 with myocardial infarction [MI] and 26 with unstable angina [UA]) and 20 patients with stable angina (SA). EMPs in platelet-poor plasma were measured flow cytometrically with combinations of fluorescent antibodies (anti-CD31, -51, -42), allowing distinction of EMPs from platelet microparticles (PMPs). Clinical subgroups of patients were correlated with EMP and PMP levels in blood.

RESULTS

Two species of EMPs (CD31+ and CD51+) were evaluated. Both were significantly higher in patients with CAD than in control subjects. CD31+ EMP was higher in ACS than SA. Among patients with first MI, CD31+ EMP was higher in patients with MI than in patients with UA and was significantly higher than in patients with recurring MI. CD51+ EMP did not discriminate ACS from SA. A simultaneous assay of PMP showed correlation between EMPs and PMPs. However, PMPs did not discriminate patients with SA from control subjects.

CONCLUSIONS

EMP assay appears promising for assessing EC injury in CAD.

Apoptotic and necrotic blebs in epithelial cells display similar neck diameters but different kinase dependency

Apoptotic and necrotic blebs elicited by H(2)O(2) were compared in terms of dynamics, structure and underlying biochemistry in HeLa cells and Clone 9 cells. Apoptotic blebs appeared in a few minutes and required micromolar peroxide concentrations. Necrotic blebs appeared much later, prior to cell permeabilization, and required millimolar peroxide concentrations. Strikingly, necrotic blebs grew at a constant rate, which was unaffected throughout successive cycles of budding and detachment. At 1 microm diameter, the necks of necrotic and apoptotic blebs were almost identical. ATP depletion was discarded as a major factor for both types of bleb. Inhibition of ROCK-I, MLCK and p38MAPK strongly decreased apoptotic blebbing but had no effect on necrotic blebbing. Taken together, these data suggest the existence of a novel structure of fixed dimensions at the neck of both types of plasma membrane blebs in epithelial cells. However, necrotic blebs can be distinguished from apoptotic blebs in their susceptibility to actomyosin kinase inhibition.

Interactions between the recipient immune system and the left ventricular assist device surface: immunological and clinical implications

The unquestionable clinical success of left ventricular assist device (LVAD) implantation has, nevertheless, been accompanied by complications arising from interactions between the implanted biomaterial and the host immune system. The aberrant state of monocyte and T-cell activation resulting from these host/device interactions is accompanied by two parallel processes: (1) selective loss of Th1 cytokine producing CD4 T-cells through activation-induced cell death; and (2) unopposed activation of Th2 cytokine producing CD4 T-cells resulting in B-cell hyperreactivity and dysregulated immunoglobulin synthesis through Th2 cytokines and heightened CD40 ligand-CD40 interactions. The net results of these events is that, on the one hand, the LVAD recipient develops progressive defects in cellular immunity and is at increased risk of serious infection, and, on the other hand, is more likely to develop allosensitization, posing a significant risk to successful transplant outcome. Intravenous immunoglobulin therapy is an effective and safe modality for sensitized LVAD recipients awaiting cardiac transplantation, reducing serum anti-human lymphoicyte antigen (HLA) alloreactivity and shortening the duration to transplantation. The therapeutic and safety profile of intravenous immunoglobulin would appear to be superior to plasmapheresis. Immunosuppression incorporating intravenous cyclophosphamide before and after transplantation is safe and highly effective in sensitized LVAD recipients of cardiac transplantation. When used after transplantation as part of triple immunosuppressive regimens, cyclophosphamide is superior to mycophenolate mofetil in reducing episodes of allograft rejection in these patients. Because these immune dysfunctions appear to be related to the effects of excessive biomaterial-associated T-cell activation, future efforts will need to be directed at either altering the physical properties of the materials interacting with the host circulation or pharmacological intervention aimed more selectively at inhibiting T-cell activation.

Pre-eclampsia and thrombophilia

Pre-eclampsia is a major cause of perinatal and maternal morbidity and mortality worldwide. Although knowledge of the precise aetiology remains uncertain a number of risk factors have been described. Thrombophilias have been associated with pre-eclampsia in a number of studies and it is biologically plausible that they may contribute to the uteroplacental thrombosis that is frequently seen in pre-eclampsia. If this association is confirmed, there is the potential to investigate preventive treatments, including low-molecular-weight heparins, aspirin and folate.

Aspects of hydrodynamic shear regulating shear-induced platelet activation and self-association of von Willebrand factor in suspension

The binding of plasma von Willebrand factor (VWF) to platelet receptor GpIb under high hydrodynamic shear leads to platelet activation and subsequent shear-induced platelet aggregation (SIPA). We quantitatively examined the aspects of fluid flow that regulate platelet activation by subjecting human blood and isolated platelets to well-defined shear conditions in a cone-plate viscometer. We made the following observations. First, Annexin V binding to phosphatidyl serine expressed on activated cells was detectable within 10 seconds of shear application. Second, fluid shear stress rather than shear rate controls platelet activation, and a threshold shear stress of approximately 80 dyn/cm(2) is necessary to induce significant activation. Under these conditions, individual domains of soluble VWF and platelet GpIb are subjected to similar magnitudes of fluid forces on the order of 0.1 pN, whereas GpIb with bound VWF is subjected to 1 pN. Third, cell-cell collisions and time-varying stresses are not essential for platelet activation. Fourth, the mechanism of platelet activation can be resolved in 2 steps based on the contribution of VWF and fluid forces. Fluid shear and VWF are required during the first step, when GpIb-VWF binding likely occurs. Subsequently, high shear forces alone in the absence of VWF in suspension can induce platelet activation. In other experiments, purified VWF was subjected to shear in the viscometer, and VWF morphology was assessed using light scattering. These studies demonstrate, for the first time, the ability of hydrodynamic forces to induce VWF aggregation in suspension. This VWF self-association may be an additional feature involved in controlling cell adhesion rates in circulation.