Biomedical subjects

Fabio Fischetti

Publications and source records attributed to Fabio Fischetti.

6 recordsLinked to original sources

PubMed2006

Cross-talk between the complement system and endothelial cells in physiologic conditions and in vascular diseases.

The endothelial layer represents a continuous physical barrier that controls coagulation and allows selective passage of soluble molecules and circulating cells across the vessel wall into the tissue. The functional activity of the endothelial cells may be influenced by their interaction with components of the complement system. In this review we shall discuss the complex interplay that can be established between the endothelium and complement proteins or activation products. Endothelial cells may also secrete several complement components which contribute to the circulating pool. This process can be regulated by cytokines and other pro-inflammatory stimuli. In addition, complement activation products stimulate endothelial cells to acquire a pro-inflammatory and pro-coagulant status. Expression of regulatory molecules on the cell surface provides protection against an undesired attack by complement activation products. Unrestricted complement activation under pathological conditions may lead to structural and functional changes of the endothelium resulting in vascular disease.

Atherosclerosis↗

PubMed2005

Thrombus formation induced by antibodies to beta2-glycoprotein I is complement dependent and requires a priming factor.

We monitored the number of intravascular platelet-leukocyte aggregates (PLAs) and thrombotic occlusions (TOs) by intravascular microscopy in the mesentery of rats receiving antiphospholipid (aPL) immunoglobulin G (IgG) purified from the sera of patients with antiphospholipid syndrome. aPL IgG had no procoagulant effect, but it caused rapid endothelial deposition of fibrinogen, followed by PLA and TO in rats receiving an intraperitoneal injection of bacterial lipopolysaccharide 3 hours before IgG infusion. Anti-beta2-glycoprotein I-depleted aPL IgG failed to induce PLAs and TOs. C3 and C9 colocalized with aPL IgG on the mesenteric vessels. The number of PLAs and TOs was markedly reduced in C6-deficient rats and in animals treated with anti-C5 miniantibody, suggesting the contribution of the terminal complement (C) complex to the aPL antibody-mediated intravascular thrombosis. In conclusion, our data indicate that antibodies to beta2-glycoprotein I trigger coagulation subsequent to a priming proinflammatory factor and that the terminal C complex is the main mediator of the coagulation process.

Animals↗

PubMed2005

The complement system at the fetomaternal interface.

The placenta has a unique structural organization that allows fetal cells expressing paternal alloantigens to establish a peaceful cohabitation with the maternal immune system. The fetal cells are continuously exposed to the humoral and cellular components of the maternal immune system present in the maternal blood that circulates in the intervillous space and in the decidual vessels. This review deals with the role played by the complement system at the placental level both in physiological and pathological conditions of pregnancies. Complement components found in the placental tissue derive to a large extent from blood circulating in placental vessels. However, some complement components may also be produced locally by macrophages and other cell types. Deposition of complement components at tissue level is usually found in association with inflammatory diseases. This is not the case in placentae in which deposits of complement components can also be documented in physiological conditions not resulting in fetal damage. Protection of the semiallogenic human conceptus against maternal complement activation products is achieved by surface expression of complement regulators that act at different steps of the complement sequence. These complement regulators are localized in a strategic position on the surface of villous trophoblast protecting the fetus from the damage that may derive from uncontrolled complement activation. However, pathological conditions of pregnancies may lead to deposition of a higher amount of complement activation products that may exceed the protection of local complement regulators.

Animals↗

PubMed2004

Platelet-activating factor and kinin-dependent vascular leakage as a novel functional activity of the soluble terminal complement complex.

The infrequent occurrence of septic shock in patients with inherited deficiencies of the terminal complement components experiencing meningococcal disease led us to suspect that the terminal complement complex is involved in vascular leakage. To this end, the permeabilizing effect of the cytolytically inactive soluble terminal complement complex (SC5b-9) was tested in a Transwell system measuring the amount of fluorescein-labeled BSA (FITC-BSA) leaked through a monolayer of endothelial cells. The complex caused increased permeability to FITC-BSA after 15 min as opposed to the prompt response to bradykinin (BK). The effect of SC5b-9 was partially reduced by HOE-140 or CV-3988, two selective antagonists of BK B2 and platelet-activating factor receptors, respectively, and was completely neutralized by the mixture of the two antagonists. Also, DX-88, a specific inhibitor of kallikrein, partially inhibited the activity of SC5b-9. The permeabilizing factor(s) released after 30 min of incubation of endothelial cells with SC5b-9 caused a prompt leakage of albumin like BK. Intravital microscopy confirmed both the extravasation of circulating FITC-BSA across mesenteric microvessels 15 min after topical application of SC5b-9 and the complete neutralization by the mixture of HOE-140 and CV-3988. SC5b-9 induced opening of interendothelial junctions in mesenteric endothelium documented by transmission electron microscopy.

Animals↗

PubMed2002

Cytolytically inactive terminal complement complex causes transendothelial migration of polymorphonuclear leukocytes in vitro and in vivo.

Intravital microscopy was used to monitor leukocyte traffic across rat mesenteric postcapillary venules induced by the inactive terminal complement (C) complex (iTCC) topically applied to ileal mesentery. Leukocytes started rolling within 15 minutes from the administration of iTCC, and by 1 hour they adhered almost completely to the endothelium emigrating from the vessels in the next 3 hours. C5a caused a similar, though less marked, effect, whereas boiled iTCC was inactive, excluding the contribution of contaminating lipopolysaccharide. The complex stimulated the migration of polymorphonuclear neutrophils (PMNs) across endothelial cells (ECs) in a transwell system after a 4-hour incubation of ECs with iTCC added to the lower chamber of the transwell, whereas a 30-minute incubation was sufficient for C5a and interleukin (IL)-8 to induce the passage of PMNs. C5a was not responsible for the effect of iTCC because this complex had no chemotactic activity and contained too small an amount of C5a to account for the transendothelial migration of PMNs. Similarly, the effect of iTCC was not mediated by IL-8 released by stimulated ECs because anti-IL-8 failed to inhibit the migration of PMNs induced by the complex. Unlike tumor necrosis factor-alpha, iTCC did not cause the redistribution of platelet-endothelial cell adhesion molecule-1 (PECAM-1), and PMN mobilization was partially blocked by anti-PECAM-1 antibodies.

Animals↗

PubMed2002

The cleavage site of C5 from man and animals as a common target for neutralizing human monoclonal antibodies: in vitro and in vivo studies.

The isolation of an anti-C5 single-chain fragment variable (scFv) antibody, TS-A12/22, from a human phage display library, is described. This antibody inhibits the activation of C5 and the assembly of the terminal complement complex implicated in cell and tissue damage. Using antibody-sensitized sheep erythrocytes and rabbit red cells as target cells in hemolytic assays, we found that TS-A12/22 inhibited the activation of C5 by the convertases of both classical and alternative pathways. Western blot analysis and competition experiments with synthetic peptides showed that TS-A12/22 reacted with the alpha chain of C5 and recognized the cleavage site of this complement component by the C5 convertase. As a result, the antibody prevented splitting of C5 and inhibited the generation of C5a and of the terminal complement complex. The identification of the TS-A12/22 recognition site as a conserved sequence in man, mouse, rat and rabbit enabled the demonstration of in vitro inhibition of complement activity in these species. The scFv TS-A12/22 was tested in a rat model of antigen-induced arthritis and proved to be effective in preventing influx of polymorphonuclear cells into the knee joint and C9 deposition on synovial tissue.

Animals↗