Biomedical subjects
J Savill
Publications and source records attributed to J Savill.
Mesangial cell apoptosis: the major mechanism for resolution of glomerular hypercellularity in experimental mesangial proliferative nephritis.
Increases in mesangial cell number may herald glomerular scarring, but they are not irreversible. This study sought mechanisms by which surplus glomerular mesangial cells can be cleared. A small proportion of cultured mesangial cells exhibited typical morphological features of apoptosis (programmed cell death), which was increased by growth factor deprivation or exposure to cycloheximide, stimuli known to increase apoptosis in other cell types. Apoptosis was confirmed by typical internucleosomal chromatin cleavage. In vivo, clear morphological evidence of mesangial apoptosis leading to phagocytosis by neighboring mesangial cells was obtained in self-limited mesangial proliferation induced in rats by Thy1.1 antibody, apoptosis occurring approximately 10-fold more frequently than in the healthy rat glomerulus. Indeed, changes in glomerular cell number in Thy1.1 nephritis strongly suggested that apoptosis is the major cell clearance mechanism counterbalancing cell division, thereby mediating resolution of glomerular hypercellularity in experimental mesangial proliferation.
Apoptosis and the kidney.
Apoptosis is a programmed form of cell death mediating the precisely controlled deletion of "unwanted" cells. This review discusses the key features of this cell death program, emphasizing that apoptosis is regulated by factors extrinsic and intrinsic to the dying cell. Furthermore, because apoptosis leads to the swift phagocytic clearance of intact cells, tissues are protected against the noxious effect of cell contents. Apoptosis occurs in the developing and adult kidney, and nephrologists now need to consider whether abnormalities of this program may contribute to renal disease. Evidence suggests that such defects could contribute to developmental abnormalities including polycystic disease, induce autoimmunity to renal tissue, and exacerbate renal inflammation and scarring. Finally, apoptosis may offer new avenues for therapy.
A possible role for bcl-2 in regulating T-cell memory--a 'balancing act' between cell death and survival.
One of the central questions in T-cell immunity is how the generation of T-cell memory may proceed simultaneously with the maintenance of T-cell homeostasis. In this article, we present a hypothesis that the regulation of bcl-2 gene expression within the activated CD45RO+ T-cell population may be one of the key factors in the balance between death and survival of these activated mature T cells, both in vitro and in vivo.
Phagocyte recognition of cells undergoing apoptosis.
A key feature of apoptosis is that cells undergoing this programmed form of death are recognized by phagocytes and ingested while still intact, protecting tissues from the potentially harmful consequences of exposure to the contents of the dying cells. This article reviews recent data which indicate that phagocyte recognition of apoptotic cells as 'senescent-self' involves at least three classes of receptors on the phagocyte surface, while apoptotic cells may display their 'edible' status in a number of different ways.
The fate of the neutrophil in vasculitis.
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Apoptosis in human eosinophils. Programmed cell death in the eosinophil leads to phagocytosis by macrophages and is modulated by IL-5.
Eosinophils are believed to injure tissues in a variety of allergic disease by virtue of their highly histotoxic contents and metabolites. They are readily observed in tissues during the allergic response yet the mechanisms governing the duration of tissue residence and route of removal remain obscure. We have previously reported in vitro and in vivo evidence that neutrophils undergo apoptosis (programmed cell death) and are recognized and ingested as intact cells by macrophages. We report that eosinophils, purified from the peripheral blood of asymptomatic healthy atopics, undergo apoptosis in vitro. After 72 to 96 h in culture, 57.0 +/- 6.2% (mean +/- SE) of the eosinophil population showed characteristic morphologic changes of apoptosis. Electrophoresis of the DNA from these cells demonstrated the typical "ladder" pattern of internucleosomal DNA cleavage, the hallmark of apoptosis-associated endonuclease activation. The rate of eosinophil apoptosis, slower than that reported for neutrophils, was delayed (by 80 +/- 6 h) in the presence of recombinant human IL-5, a cytokine previously reported to prolong eosinophil life in vitro but not known to modulate apoptosis. Aged, apoptotic eosinophils, but not fresh or aged preapoptotic eosinophils, were recognized and ingested as intact cells by macrophages. Apoptosis and ingestion by macrophages may represent a mechanism whereby the tissue longevity and removal of eosinophils is controlled.
Glomerular mesangial cells and inflammatory macrophages ingest neutrophils undergoing apoptosis.
Apoptosis or programmed cell death of senescent neutrophils leading to their uptake by phagocytes is a general mechanism by which neutrophils may be removed from inflamed sites in vivo, promoting resolution rather than persistence of inflammation. We now report morphological evidence of neutrophil apoptosis leading to uptake by glomerular cells in rats with experimental glomerulonephritis. In addition to confirming that inflammatory macrophages take up apoptotic neutrophils, these studies indicated that glomerular mesangial cells can also participate in this mode of neutrophil clearance. Furthermore, human neutrophils which had been "aged" in vitro so as to undergo apoptosis were ingested by 31.5 +/- 1.3% (mean +/- SE) of cultured human mesangial cells, but there was minimal recognition of freshly isolated neutrophils (2.2 +/- 0.1%). Centrifugal elutriation of aged neutrophil populations yielded fractions with varying degrees of apoptosis (from 11.1 to 79.4%). Uptake of these fractions (by 8.2% to 59.8% of mesangial cells) was closely correlated with apoptosis (r = 0.96, P less than 0.0001). This demonstrated that recognition was dependent upon apoptosis, as in previous reports of macrophage recognition of aged neutrophils. However, by contrast, a partial requirement for serum was observed. These data indicate a hitherto unexpected function for the mesangial cell in clearance of senescent neutrophils from the glomerulus which may supplement inflammatory macrophage uptake of leucocytes undergoing apoptosis.
Apoptosis: a mechanism for regulation of the cell complement of inflamed glomeruli.
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Macrophage recognition of senescent neutrophils.
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Thrombospondin cooperates with CD36 and the vitronectin receptor in macrophage recognition of neutrophils undergoing apoptosis.
We have investigated the cell surface recognition mechanisms used by human monocyte-derived macrophages (M phi) in phagocytosis of intact aging human neutrophils (PMNs) undergoing apoptosis. This study shows that the adhesive protein thrombospondin (TSP) was present in the interaction, both associated with the M phi surface and in solution at a mean concentration of 0.59 micrograms/ml. The interaction was inhibited by treatment of M phi (but not aged PMN) with cycloheximide, but could be "rescued" by replenishment with exogenous TSP. Under control conditions, M phi recognition of aged PMNs was specifically potentiated by purified platelet TSP at 5 micrograms/ml, present either in the interaction or if preincubated with either cell type, suggesting that TSP might act as a "molecular bridge" between the two cell types. In support, both aged PMN and M phi were found to adhere to TSP, and phagocytosis of aged PMN was specifically inhibited by (a) excess soluble TSP; (b) antibodies to TSP that also inhibit TSP-mediated adhesion to aged PMN; and (c) down-regulation of M phi receptors for TSP by plating M phi on TSP-coated surfaces. Furthermore, inhibition with mAbs/Arg-Gly-Asp-Ser peptide of the candidate M phi receptors for TSP, CD36, and alpha v beta 3 exerted synergistic effects on both M phi recognition of aged PMN and M phi adhesion to TSP, indicating that "two point" adhesion of TSP to these M phi structures is involved in phagocytosis of aged PMN. Our findings indicate newly defined roles for TSP and CD36 in phagocytic clearance of senescent neutrophils, which may limit inflammatory tissue injury and promote resolution.
Apolipoprotein E polymorphism and plasma lipid, lipoprotein, and apolipoprotein levels in Italian children.
We have investigated the effect of apolipoprotein (apo) E polymorphism on serum lipid, lipoprotein, and apolipoprotein levels in a sample of 195 children, aged 8-11 years, from Sezze, Central Italy. The relative frequencies of e2, e3, and e4 alleles were 0.062, 0.867, and 0.072, respectively. Variation at the apo E gene locus explained 5.1% of the sample variance in serum total cholesterol levels, 7.6% in low-density lipoprotein (LDL) cholesterol levels, 7.3% in apo B levels, and 14.1% in high-density lipoprotein-apo E (HDL-E) levels. The effect of the e2 allele was to lower levels of total cholesterol, LDL-cholesterol, and apo B and to raise levels of HDL-E, while the effect of the e4 allele was the opposite. Variation at the apo E gene locus was not associated with differences in serum triglyceride, HDL-cholesterol, or apo AI levels. The effects of common apo E polymorphisms and genetic variation associated with the PvuII RFLP of the apo B gene on serum apo B levels were additive, explaining 11.3% of the phenotypic variance in this sample. When the effect of apo E polymorphism on serum lipid traits was estimated in boys and girls separately, variation at the apo E gene locus explained 10.4, 13.3, 13.3, and 13.5% of the phenotypic variance in serum total cholesterol, LDL-cholesterol, apo B, and HDL-E levels, respectively, in boys, while in girls only the effect on HDL-E levels (19.3%) reached statistical significance. This study has demonstrated that genetic variations at the apo E locus contribute to the determination of serum lipid, lipoprotein, and apolipoprotein levels in youths and that the effects are gender specific.
A 19-year-old man with leucocyte adhesion deficiency. In vitro and in vivo studies of leucocyte function.
We describe a male patient with leucocyte adhesion molecule deficiency (LAD) of moderate phenotype. Although diagnosis was made only 2 years before his death, the patient survived until 19 years of age. This enabled us to perform a number of novel investigation, both in vivo and in vitro, relating to his leucocyte biology. Monocytes cultured in vitro matured into morphologically normal, phagocytically capable macrophages, which were able to recognize aged 'apoptotic' neutrophils. By injection of radiolabelled autologous neutrophils we demonstrated a prolonged neutrophil half-life, but normal margination, de-margination on exercise, and splenic pooling. Neutrophil adherence in vitro to vascular endothelium was normal. Histological examination of the patient's lungs at post-mortem showed intravascular aggregation of polymorphonuclear leucocytes but a paucity of cells in the interstitium and alveolar spaces. These findings indicate that the peripheral blood leucocytosis commonly observed in these patients may be due to prolonged intravascular neutrophil survival, and suggest that CD11/18 molecules have an important role in facilitating neutrophil emigration from blood vessels at sites of inflammation.
Macrophage vitronectin receptor, CD36, and thrombospondin cooperate in recognition of neutrophils undergoing programmed cell death.
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Towards a more rapid diagnosis of rapidly progressive glomerulonephritis.
An attempt was made to provide simple practical guidelines to alert general practitioners to the diagnosis of rapidly progressive glomerulonephritis and lead to early referral to hospital. The duration of illness before referral to this hospital and its effect on outcome in patients with crescentic nephritis were assessed retrospectively from the case notes of 24 patients referred over two years. Four patients had Goodpasture's syndrome, 11 Wegener's granulomatosis, seven microscopic polyarteritis, and two idiopathic progressive glomerulonephritis. The duration of symptoms before referral to the local hospital was similar in the four groups of patients and varied from one week to 28 months (mean 10 months). The duration of stay in the local hospital was two, nine, 11, and 180 days in the patients with Goodpasture's syndrome and a mean of four days (range one to eight) in those with Wegener's granulomatosis and 10 days (one to 18 days) in those with microscopic polyarteritis. In the local hospital the diagnosis was based on the results of renal biopsy and detection of antibodies to glomerular basement membrane in two patients with Goodpasture's syndrome and on the results of renal biopsy in seven of the other patients aided by the detection of antibodies to the cytoplasm of neutrophils (ANCA) in 10. Three of the 24 patients died and four required maintenance haemodialysis. Patients who present to their general practitioners with persistent non-specific symptoms should have a urine dipstick test and then blood tests and emergency referral to hospital if necessary. Hospital physicians should be aware of the speed and accuracy with which current assays can confirm a diagnosis of rapidly progressive glomerulonephritis.
Vitronectin receptor-mediated phagocytosis of cells undergoing apoptosis.
Phagocyte recognition of cells that have undergone apoptosis (programmed cell death) is an event of broad biological significance. Characterized by endogenous endonuclease activation, which results in chromatin fragmentation and nuclear condensation, apoptosis leads to swift ingestion of intact but 'senescent' or 'unwanted' cells by phagocytes in processes as diverse as the physiological involution of organs, the remodelling of embryonic tissues, and metamorphosis. The cell-surface mechanisms by which macrophages recognize apoptotic cells as 'senescent-self' have remained obscure. Here we report that macrophage recognition of apoptotic cells (both neutrophils and lymphocytes) is mediated by the vitronectin receptor, a heterodimer belonging to the beta 3 or cytoadhesin family of the integrins. Previously, the functions of the vitronectin receptor were believed to be limited to cell anchorage, but our findings indicate that the receptor has a novel and direct role in self-senescent-self intercellular recognition leading to macrophage phagocytosis of cells undergoing apoptosis.
Macrophage recognition of senescent granulocytes.
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Variation at the apolipoprotein (apo) AI-CIII-AIV gene cluster and apo B gene loci is associated with lipoprotein and apolipoprotein levels in Italian children.
We have used RFLPs of the apolipoprotein (apo) B gene and apo AI-CIII-AIV gene cluster to estimate the genetic contribution of variation at these loci to the variability of plasmid lipid, lipoprotein, and apolipoprotein levels in 209 children from Sezze in central Italy. The sample was randomly divided into group I (107 children) and group II (102 children). Four site polymorphisms (PvuII, XbaI, MspI, and EcoRI) of the apo B gene and five site polymorphisms (XmnI, PstI, SstI, PvuII-CIII, and PvuII-AIV) of the apo AI-CIII-AIV gene cluster were examined in group I children. After adjustment for gender, age, and body-mass index, polymorphisms at both gene loci (PvuII-B, PvuII-CIII, and PvuII-AIV) were associated with significant effects on the levels of plasma apo AI, apo B, or high-density lipoprotein-cholesterol. RFLPs that showed significant effects in group I were genotyped in group II. All three polymorphisms were associated with similar effects on apolipoprotein levels, though for all RFLPs the magnitude of the effects was smaller in the group II children and only statistically significant for the effect of the PvuII-B genotype on apo AI levels. In the total sample of 209 children 7.4% of the sample variance in apo AI levels was explained by variation associated with the apo B PvuII-B RFLP. In addition, the PvuII-B RFLP was associated with significant effects on plasma apo B levels and explained 5.7% of the sample variance. The PvuII-CIII and PvuII-AIV polymorphisms were both associated with differences in apo AI levels, explaining 3.7%-5.7% of the sample variance. Taken together, the three PvuII polymorphisms explained 17.7% of the phenotypic variance in apo AI levels. There was significant evidence for an effect of nonlinearity of the PvuII-CIII genotypes on apo AI levels, with the individuals heterozygous for the polymorphism having the highest apo AI levels. No evidence of interaction between genotype and gender, age, and body-mass index was shown by covariance analysis. The molecular explanation of this effect is unclear. Our data show that variation at both the apo AI-CIII-AIV and apo B loci are associated with lipoprotein and apolipoprotein levels in this sample of Italian children.