Proinflammatory stimuli enhance phagocytosis of apoptotic cells by neutrophil granulocytes.
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ABSTRACT:
SUBMITTER: Hellberg L
PROVIDER: S-EPMC3217599 | biostudies-other | 2011
REPOSITORIES: biostudies-other
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Project description:Neutrophil granulocytes are the first leukocytes that encounter and phagocytose Leishmania major (L. major) parasites in the infected skin. The parasites can nonetheless survive within neutrophils. However, the mechanisms enabling the survival of Leishmania within neutrophils are still elusive. Previous findings indicated that human neutrophils can engulf apoptotic cells. Since apoptotic neutrophils are abundant in infected tissues, we hypothesized that the uptake of apoptotic cells results in diminished anti-leishmanial activity and, consequently, contributes to enhanced survival of the parasites at the site of infection. In the present study, we demonstrated that L. major-infected primary human neutrophils acquire enhanced capacity to engulf apoptotic cells. This was associated with increased expression of the complement receptors 1 and 3 involved in phagocytosis of apoptotic cells. Next, we showed that ingestion of apoptotic cells affects neutrophil antimicrobial functions. We observed that phagocytosis of apoptotic cells by neutrophils downregulates the phosphorylation of p38 MAPK and PKC?, the kinases involved in activation of NADPH oxidase and hence reactive oxygen species (ROS) production. In line, uptake of apoptotic cells inhibits TNF- and L. major-induced ROS production by neutrophils. Importantly, we found that the survival of Leishmania in neutrophils is strongly enhanced in neutrophils exposed to apoptotic cells. Together, our findings reveal that apoptotic cells promote L. major survival within neutrophils by downregulating critical antimicrobial functions. This suggests that the induction of enhanced uptake of apoptotic cells represents a novel evasion mechanism of the parasites that facilitates their survival in neutrophil granulocytes.
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Project description:Impaired efferocytosis has been shown to be associated with, and even to contribute to progression of, chronic inflammatory diseases such as atherosclerosis. Enhancing efferocytosis has been proposed as strategy to treat diseases involving inflammation. Here we present the strategy to increase 'eat me' signals on the surface of apoptotic cells by targeting cell surface-expressed phosphatidylserine (PS) with a variant of annexin A5 (Arg-Gly-Asp-annexin A5, RGD-anxA5) that has gained the function to interact with ?(v)?(3) receptors of the phagocyte. We describe design and characterization of RGD-anxA5 and show that introduction of RGD transforms anxA5 from an inhibitor into a stimulator of efferocytosis. RGD-anxA5 enhances engulfment of apoptotic cells by phorbol-12-myristate-13-acetate-stimulated THP-1 (human acute monocytic leukemia cell line) cells in vitro and resident peritoneal mouse macrophages in vivo. In addition, RGD-anxA5 augments secretion of interleukin-10 during efferocytosis in vivo, thereby possibly adding to an anti-inflammatory environment. We conclude that targeting cell surface-expressed PS is an attractive strategy for treatment of inflammatory diseases and that the rationally designed RGD-anxA5 is a promising therapeutic agent.
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Project description:Natural antibodies, which arise without known immune exposure, have been described that specifically recognize cells dying from apoptosis but their role in innate immunity remains poorly understood. Herein, we show that the immune response to neo-antigenic determinants on apoptotic thymocytes is dominated by antibodies to oxidation-associated antigens, phosphorylcholine (PC), a head group that becomes exposed during programmed-cell death, and malondialdehyde (MDA), a reactive aldehyde degradation product of polyunsaturated lipids produced following exposure to reactive-oxidation species. While natural antibodies to apoptotic cells in naM-CM-/ve adult mice were dominated by PC and MDA specificities, the amounts of these antibodies were substantially boosted by treatment of mice with apoptotic cells. Moreover, the relative amounts of PC and MDA antibodies was affected by VH gene inheritance. Antibody interactions with apoptotic-cells also mediated the recruitment of C1q, which alone can promote apoptotic-cell phagocytosis by immature dendritic cells. Significantly, IgM-antibodies to both PC and MDA were primary factors in determining the efficiency of serum-dependent apoptotic-cell phagocytosis. Hence, we demonstrate a mechanism by which certain natural antibodies that recognize neo-antigens on apoptotic cells, in naM-CM-/ve mice and those induced by immune exposure to apoptotic-cells, can enhance the functional capabilities of immature dendritic cells for phagocytic engulfment of apoptotic cells. Keywords: Natural antibodies, Inflammation, Complement, Apoptosis In the study presented here, a total of 11 custom-spotted protein slides were hybridized with a T15 IgM monoclonal antibody at three different concentrations, an isotype control IgM, 2 slides were hybridized with serum from naM-QM-^Wve mice, 2 slides incubated with serum from mice immunized with apoptotic cells, 2 slides were incubated with serum from mice immunized with saline, and a negative control slide with no antibody hybridized
2009-02-23 | E-GEOD-14958 | biostudies-arrayexpress
Project description:Natural Abs, which arise without known immune exposure, have been described that specifically recognize cells dying from apoptosis, but their role in innate immunity remains poorly understood. Herein, we show that the immune response to neoantigenic determinants on apoptotic thymocytes is dominated by Abs to oxidation-associated Ags, phosphorylcholine (PC), a head group that becomes exposed during programmed cell death, and malondialdehyde (MDA), a reactive aldehyde degradation product of polyunsaturated lipids produced following exposure to reactive oxidation species. While natural Abs to apoptotic cells in naive adult mice were dominated by PC and MDA specificities, the amounts of these Abs were substantially boosted by treatment of mice with apoptotic cells. Moreover, the relative amounts of PC and MDA Abs was affected by V(H) gene inheritance. Ab interactions with apoptotic cells also mediated the recruitment of C1q, which enhanced apoptotic cell phagocytosis by immature dendritic cells. Significantly, IgM Abs to both PC and MDA were primary factors in determining the efficiency of serum-dependent apoptotic cell phagocytosis. Hence, we demonstrate a mechanism by which certain natural Abs that recognize neoantigens on apoptotic cells, in naive mice and those induced by immune exposure to apoptotic cells, can enhance the functional capabilities of immature dendritic cells for phagocytic engulfment of apoptotic cells.
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Project description:Polyreactive antibodies are a major component of the natural antibody repertoire and are capable of binding a variety of structurally unrelated antigens. Many of the properties attributed to natural antibodies, in fact, are turning out to be due to polyreactive antibodies. In humans, each day, billions of cells undergo apoptosis. In the present experiments, we show by ImageStream technology that although polyreactive antibodies do not bind to live T cells they bind to both the plasma membrane and cytoplasm of late apoptotic cells, fix complement, generate the anaphylatoxin C5a and increase by as much as 5 fold complement-mediated phagocytosis by macrophages. Of particular importance, T cells undergoing apoptosis following infection with HIV also bind polyreactive antibodies and are phagocytosed. We conclude that the polyreactive antibodies in the natural antibody repertoire contribute in a major way to the clearance of cells made apoptotic by a variety of natural and infectious processes.
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Project description:Apoptosis is a noninflammatory, programmed form of cell death. One mechanism underlying the non-phlogistic nature of the apoptosis program is the swift phagocytosis of the dying cells. How apoptotic cells attract mononuclear phagocytes and not granulocytes, the professional phagocytes that accumulate at sites of inflammation, has not been determined. Here, we show that apoptotic human cell lines of diverse lineages synthesize and secrete lactoferrin, a pleiotropic glycoprotein with known antiinflammatory properties. We further demonstrated that lactoferrin selectively inhibited migration of granulocytes but not mononuclear phagocytes, both in vitro and in vivo. Finally, we were able to attribute this antiinflammatory function of lactoferrin to its effects on granulocyte signaling pathways that regulate cell adhesion and motility. Together, our results identify lactoferrin as an antiinflammatory component of the apoptosis milieu and define what we believe to be a novel antiinflammatory property of lactoferrin: the ability to function as a negative regulator of granulocyte migration.
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Project description:Natural antibodies, which arise without known immune exposure, have been described that specifically recognize cells dying from apoptosis but their role in innate immunity remains poorly understood. Herein, we show that the immune response to neo-antigenic determinants on apoptotic thymocytes is dominated by antibodies to oxidation-associated antigens, phosphorylcholine (PC), a head group that becomes exposed during programmed-cell death, and malondialdehyde (MDA), a reactive aldehyde degradation product of polyunsaturated lipids produced following exposure to reactive-oxidation species. While natural antibodies to apoptotic cells in naïve adult mice were dominated by PC and MDA specificities, the amounts of these antibodies were substantially boosted by treatment of mice with apoptotic cells. Moreover, the relative amounts of PC and MDA antibodies was affected by VH gene inheritance. Antibody interactions with apoptotic-cells also mediated the recruitment of C1q, which alone can promote apoptotic-cell phagocytosis by immature dendritic cells. Significantly, IgM-antibodies to both PC and MDA were primary factors in determining the efficiency of serum-dependent apoptotic-cell phagocytosis. Hence, we demonstrate a mechanism by which certain natural antibodies that recognize neo-antigens on apoptotic cells, in naïve mice and those induced by immune exposure to apoptotic-cells, can enhance the functional capabilities of immature dendritic cells for phagocytic engulfment of apoptotic cells. Keywords: Natural antibodies, Inflammation, Complement, Apoptosis
2009-02-23 | GSE14958 | GEO
Project description:To identify molecules that play roles in the clearance of apoptotic cells by Drosophila phagocytes, we examined a series of monoclonal antibodies raised against larval hemocytes for effects on phagocytosis in vitro. One antibody that inhibited phagocytosis recognized terribly reduced optic lobes (Trol), a core protein of the perlecan-type proteoglycan, and the level of phagocytosis in embryos of a Trol-lacking fly line was lower than in a control line. The treatment of a hemocyte cell line with a recombinant Trol protein containing the amino acid sequence RGD augmented the phosphorylation of focal adhesion kinase, a hallmark of integrin activation. A loss of integrin ??, one of the two ? subunits of Drosophila integrin, brought about a reduction in the level of apoptotic cell clearance in embryos. The presence of integrin ?? at the surface of embryonic hemocytes was confirmed, and forced expression of integrin ?? in hemocytes of an integrin ??-lacking fly line recovered the defective phenotype of phagocytosis. Finally, the level of phagocytosis in a fly line that lacks both integrin ?? and Draper, another receptor required for the phagocytosis of apoptotic cells, was lower than that in a fly line lacking either protein. We suggest that integrin ?? serves as a phagocytosis receptor responsible for the clearance of apoptotic cells in Drosophila, independent of Draper.
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