No abstract

Pentraxins are acute-phase proteins produced in vivo during inflammatory reactions. Classical short pentraxins, C-reactive protein, and serum amyloid P component are generated in the liver in response to interleukin (IL)–6. The long pentraxin PTX3 is produced in tissues under the control of primary proinflammatory signals, such as lipopolysaccharide, IL-1β, and tumor necrosis factor-α, which also promote maturation of dendritic cells (DCs). Cell death commonly occurs during inflammatory reactions. In this study, it is shown that PTX3 specifically binds to dying cells. The binding was dose dependent and saturable. Recognition was restricted to extranuclear membrane domains and to a chronological window after UV irradiation or after CD95 cross-linking–induced or spontaneous cell death in vitro. PTX3 bound to necrotic cells to a lesser extent. Human DCs failed to internalize dying cells in the presence of PTX3, while they took up normally soluble or inert particulate substrates. These results suggest that PTX3 sequesters cell remnants from antigen-presenting cells, possibly contributing to preventing the onset of autoimmune reactions in inflamed tissues.

Objective. Phagocytosis of apoptotic cells can be facilitated by complement components and short pentraxins, such as serum amyloid P (SAP). In contrast, the long pentraxin PTX3 was shown to inhibit phagocytosis of apoptotic Jurkat cells by dendritic cells and to bind late apoptotic polymorphonuclear leukocytes (PMNs). Recently, levels of the pentraxin PTX3 were shown to parallel disease activity in small-vessel vasculitis, which is often characterized by leukocytoclasia, a persistence of leukocyte remnants in the vessel wall. We undertook this study to test our hypothesis that PTX3 inhibits phagocytosis of late apoptotic PMNs by macrophages, thereby leading to their accumulation in the vessel wall.Methods. Macrophages were allowed to phagocytose late apoptotic or secondary necrotic PMNs that were incubated with or without PTX3 for 30 minutes prior to phagocytosis. Phagocytosis was allowed to occur in the presence of 30% normal human serum with or without SAP and with or without depletion of complement. To discriminate between an inhibitory effect of PTX3 on binding and the internalization of apoptotic PMNs into macrophages, internalization was blocked by cytochalasin B.Results. SAP and complement were both necessary for effective in vitro phagocytosis. In contrast, PTX3 inhibited phagocytosis in a dose-dependent manner, from 11% inhibition at 6.25 g/ml to almost complete inhibition at 100 g/ml. Furthermore, PTX3 partly affected binding of apoptotic PMNs to macrophages.Conclusion. PTX3, in contrast to SAP and complement, inhibits phagocytosis of late apoptotic PMNs by monocyte-derived macrophages in a dose-dependent manner. Therefore, PTX3 can play a role in the development of leukocytoclasia by affecting the clearance of apoptotic PMNs, thereby inducing their accumulation in the vessel wall.

No abstract

Objective. The prototypical tissue pentraxin PTX3 inhibits phagocytosis of late apoptotic polymorphonuclear leukocytes (PMNs) by macrophages. Levels of PTX3 parallel disease activity in small-vessel vasculitis. Small-vessel vasculitis is often characterized by leukocytoclasia, a phenomenon of accumulation of nuclear remnants from unscavenged PMNs in or near the vessel wall. We therefore hypothesized that PTX3 accumulates at sites of leukocytoclastic vasculitis and, as such, is a key factor for the induction of leukocytoclasis.Methods. We examined skin biopsy samples from 13 patients with small-vessel vasculitis and from 4 healthy and 3 inflammatory skin disease controls. Biopsy tissues, characterized histopathologically as leukocytoclastic vasculitis, were studied for the presence of PTX3 using rabbit anti-PTX3 polyclonal antibodies. Sections were scored morphometrically for leukocytoclastic infiltrates in conjunction with PTX3 staining. Morphometric scores were expressed as percentages of staining of the total tissue area.Results. Biopsy specimens from patients with leukocytoclastic vasculitis revealed an abundant upregulation of PTX3 at sites of leukocytoclastic infiltrates. Significantly more PTX3 was found in tissues from the 13 patients with vasculitis (mean ؎ SEM 48.9 ؎ 6.1%) than in tissues from the 7 controls (4.5 ؎ 2.7%) (P ‫؍‬ 0.0003). PTX3 was localized around vessels, as well as spread diffusely throughout the tissue.Conclusion. PTX3 is abundantly present at sites of leukocytoclastic infiltrates in patients with smallvessel vasculitis, but not in controls. Since PTX3 inhibits phagocytosis of late apoptotic PMNs by macrophages and is strongly up-regulated at sites of leukocytoclastic infiltration, PTX3 is a candidate factor in the phenomenon of leukocytoclasia in small-vessel vasculitis.

Pentraxins are acute-phase proteins produced in vivo during inflammatory reactions. Classical short pentraxins, C-reactive protein, and serum amyloid P component are generated in the liver in response to interleukin (IL)–6. The long pentraxin PTX3 is produced in tissues under the control of primary proinflammatory signals, such as lipopolysaccharide, IL-1β, and tumor necrosis factor-α, which also promote maturation of dendritic cells (DCs). Cell death commonly occurs during inflammatory reactions. In this study, it is shown that PTX3 specifically binds to dying cells. The binding was dose dependent and saturable. Recognition was restricted to extranuclear membrane domains and to a chronological window after UV irradiation or after CD95 cross-linking–induced or spontaneous cell death in vitro. PTX3 bound to necrotic cells to a lesser extent. Human DCs failed to internalize dying cells in the presence of PTX3, while they took up normally soluble or inert particulate substrates. These results suggest that PTX3 sequesters cell remnants from antigen-presenting cells, possibly contributing to preventing the onset of autoimmune reactions in inflamed tissues.