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Biomedical subjects

A Devitt

Publications and source records attributed to A Devitt.

17 recordsLinked to original sources
PubMed2003

CD14-dependent clearance of apoptotic cells by human macrophages: the role of phosphatidylserine.

Apoptotic-cell clearance is dependent on several macrophage surface molecules, including CD14. Phosphatidylserine (PS) becomes externalised during apoptosis and participates in the clearance process through its ability to bind to a novel receptor, PS-R. CD14 has the proven ability to bind phospholipids and may function as an alternative receptor for the externalised PS of apoptotic cells. Here we demonstrate that CD14 does not function preferentially as a PS receptor in apoptotic-cell clearance. Compared with phosphatidylcholine and phosphatidylethanolamine, PS was the least active phospholipid binding to human monocyte-derived macrophages and showed no specificity for soluble or membrane-anchored CD14. Significantly, PS-containing liposomes failed to inhibit CD14-dependent uptake of apoptotic cells by macrophages. PS exposure was, however, found to be insufficient for either CD14-dependent or CD14-independent apoptotic-cell uptake by phagocytes. The additional features that enable apoptotic-cell clearance are derived from mechanisms that can be divorced temporally from those responsible for the morphological features of apoptosis.

Annexin A5↗
PubMed2003

Macrophage-mediated clearance of cells undergoing caspase-3-independent death.

Little is known of the functions of caspases in mediating the surface changes required for phagocytosis of dying cells. Here we investigate the role played by the effector caspase, caspase-3 in this process using the caspase-3-defective MCF-7 breast carcinoma line and derived caspase-3-expressing transfectants. Our results indicate that, while certain typical features of apoptosis induced by etoposide--namely classical morphological changes and the ability to degrade DNA into oligonucleosomal fragments - are caspase-3-dependent, loss of cell adhesion to plastic and the capacity to interact with, and to be phagocytosed by, human monocyte-derived macrophages - both by CD14-dependent and CD14-independent mechanisms--do not require caspase-3. Furthermore, both etoposide-induced caspase-3-positive and -negative MCF-7 cells suppressed proinflammatory cytokine release by macrophages. These results demonstrate directly that cell surface changes that are sufficient for anti-inflammatory clearance by human macrophages can be regulated independently of stereotypical features of the apoptosis programme that require caspase-3.

Annexin A5↗
PubMed2001

Serum response factor cleavage by caspases 3 and 7 linked to apoptosis in human BJAB cells.

Apoptosis involves the cessation of cellular processes, the breakdown of intracellular organelles, and, finally, the nonphlogistic clearance of apoptotic cells from the body. Important for these events is a family of proteases, caspases, which are activated by a proteolytic cleavage cascade and drive apoptosis by targeting key proteins within the cell. Here, we demonstrate that serum response factor (SRF), a transcription factor essential for proliferative gene expression, is cleaved by caspases and that this cleavage occurs in proliferating murine fibroblasts and can be induced in the human B-cell line BJAB. We identify the two major sites at which SRF cleavage occurs as Asp(245) and Asp(254), the caspases responsible for the cleavage and generate a mutant of SRF resistant to cleavage in BJAB cells. Investigation of the physiological and functional significance of SRF cleavage reveals that it correlates with the loss of c-fos expression, whereby neither SRF cleavage fragment retains transcriptional activity. Moreover, the expression of a noncleavable SRF in BJAB cells suppresses apoptosis induced by Fas cross-linking. These results suggest that for apoptosis to proceed, the transcriptional events promoting cell survival and proliferation, in which SRF is involved, must first be inactivated.

3T3 Cells↗
PubMed2000

The effect of the position of the limb on venous impulse foot pumps.

Compression foot pumps are widely used for the prevention of postoperative venous thrombosis. We tested the efficiency of the pump in ten healthy subjects; the velocity of venous blood flow in the common femoral vein was measured in the horizontal, Trendelenberg (foot-up) and reverse-Trendelenberg (foot-down) positions. Application of the foot pump produced an increase in the venous velocity in all subjects. The mean increase in the horizontal position was 27.2% and in the Trendelenberg position 15.4%. In the reverse-Trendelenberg position, the foot pump produced a mean increase of 102.8%. The efficiency of the compression foot pump in increasing venous return is improved by adopting the reverse-Trendelenberg position. This may increase its thromboprophylactic effect.

Adult↗
PubMed1999

Macrophage recognition of ICAM-3 on apoptotic leukocytes.

Cells undergoing apoptosis are cleared rapidly by phagocytes, thus preventing tissue damage caused by loss of plasma membrane integrity. In this study, we show that the surface of leukocytes is altered during apoptosis such that the first Ig-like domain of ICAM-3 (CD50) can participate in the recognition and phagocytosis of the apoptotic cells by macrophages. Macrophage recognition of apoptotic cell-associated ICAM-3 was demonstrated both on leukocytes and, following transfection of exogenous ICAM-3, on nonleukocytes. The change in ICAM-3 was a consistent consequence of apoptosis triggered by various stimuli, suggesting that it occurs as part of a final common pathway of apoptosis. Alteration of ICAM-3 on apoptotic cells permitting recognition by macrophages resulted in a switch in ICAM-3-binding preference from the prototypic ICAM-3 counterreceptor, LFA-1, to an alternative macrophage receptor. Using mAbs to block macrophage/apoptotic cell interactions, we were unable to obtain evidence that either the alternative ICAM-3 counterreceptor alpha d beta 2 or the apoptotic cell receptor alpha v beta 3 was involved in the recognition of ICAM-3. By contrast, mAb blockade of macrophage CD14 inhibited ICAM-3-dependent recognition of apoptotic cells. These results show that ICAM-3 can function as a phagocytic marker of apoptotic leukocytes on which it acquires altered macrophage receptor-binding activity.

Antibodies, Monoclonal↗
PubMed1999

CD14 and apoptosis.

In addition to its role as a mediator of innate pro-inflammatory responses following bacterial lipopolysaccharide (LPS) binding, the 55kDa glycosyl-phosphatidylinositol-linked macrophage plasma membrane glycoprotein CD14 is now also known to play a role in phagocytic clearance of apoptotic cells. Although apoptotic cell-associated ligand(s) for CD14 await definition, initial findings suggest that ligand binding occurs close to, or at the same site as, LPS binding. Significantly, in contrast to LPS clearance and in keeping with the non-phlogistic nature of apoptosis, CD14-dependent engulfment of apoptotic cells fails to elicit pro-inflammatory cytokine release from macrophages. Therefore CD14 may be regarded as an innate immune receptor both for microbial products--after binding which activates inflammatory responses--and for self components, which either fail to induce, or alternatively actively suppress, inflammatory responses. Here we review current knowledge of the structure and functions of CD14, its ligands, its possible modes of signal transduction and its place in the panoply of macrophage molecules implicated in apoptotic-cell clearance.

Journal Article↗
PubMed1999

The Internet and an orthopaedic discussion group.

Since its inception, the Internet has created many new opportunities for the dissemination of knowledge. We have developed an Internet-based orthopaedic discussion group. There are 93 members from Ireland and elsewhere in the world. Precautions are taken to ensure the confidentiality of all cases submitted to the group. All patient identifiers are removed from images, radiographs and reports before submission. In the first 18 months more than 100 cases were discussed by the group. The use of an Internet-based discussion group in orthopaedics has expanded the educational and communication opportunities for the Irish orthopaedic profession both nationally and internationally.

Education, Medical, Continuing↗
PubMed1998

Human CD14 mediates recognition and phagocytosis of apoptotic cells.

Cells undergoing programmed cell death (apoptosis) are cleared rapidly in vivo by phagocytes without inducing inflammation. Here we show that the glycosylphosphatidylinositol-linked plasma-membrane glycoprotein CD14 on the surface of human macrophages is important for the recognition and clearance of apoptotic cells. CD14 can also act as a receptor that binds bacterial lipopolysaccharide (LPS), triggering inflammatory responses. Overstimulation of CD14 by LPS can cause the often fatal toxic-shock syndrome. Here we show that apoptotic cells interact with CD14, triggering phagocytosis of the apoptotic cells. This interaction depends on a region of CD14 that is identical to, or at least closely associated with, a region known to bind LPS. However, apoptotic cells, unlike LPS, do not provoke the release of pro-inflammatory cytokines from macrophages. These results indicate that clearance of apoptotic cells is mediated by a receptor whose interactions with 'non-self' components (LPS) and 'self' components (apoptotic cells) produce distinct macrophage responses.

Animals↗
PubMed1997

16- to 25-year follow-up study of cemented arthroplasty of the hip in patients aged 50 years or younger.

The clinical outcome of the cemented Charnley hip arthroplasty at follow-up periods of 16-25 years was evaluated retrospectively in patients aged 50 years or younger. One hundred thirty-two of a total of 167 hip arthroplasties were studied. The overall probability of survival of the implant at 20 years was 75% Survival of those with rheumatoid disease was 80% compared with 64% for those with osteoarthritis. Female sex was associated with a better prognosis. Accelerated wear was associated with decreased survival of the prosthesis. Varus orientation of the femoral component significantly influenced failure (P < .01). Radiographic loosening of the acetabular component was well tolerated, but loosening of the femoral component was significantly associated with pain (P = .01).

Adolescent↗
PubMed1996

Bcl-2 delays macrophage engulfment of human B cells induced to undergo apoptosis.

The capacity to be recognized and engulfed by phagocytes is an important characteristic of cells dying by apoptosis. Phagocytosis of apoptotic cells occurs rapidly in vivo, probably prior to plasma membrane breakdown. While the molecular mechanisms mediating phagocytosis of apoptotic cells are beginning to be defined, little is yet known of the relationship between the cell-death program itself and the surface changes on the dying cells that signal for engulfment. Here, we investigate to what extent the apoptosis repressor Bcl-2 can modulate the recognition and phagocytosis of human B cells exposed to triggers of apoptosis. Burkitt lymphoma (BL)-derived, Bcl-2- B cells were induced into apoptosis either by the Ca(2+)-ionophore ionomycin or by the inhibitor of protein synthesis cycloheximide. Apoptotic BL cells, but not viable BL cells, were recognized and phagocytosed by monocyte-derived macrophages. bcl-2-transfected BL populations showed a reduced capacity both to undergo apoptosis in response to these inducing agents and to interact with macrophages. Like their Bcl-2- counterparts, Bcl-2+ BL cells interacted with macrophages only after activation of their apoptotic program as assessed by changes in nuclear morphology. These results demonstrate not only that continued protein synthesis in B cells undergoing apoptosis is not essential for their recognition by macrophages, but also that macrophage recognition of apoptotic B cells cannot be uncoupled from the cell-death program that is controlled by Bcl-2. In this respect, the behavior of B cells contrasts markedly with that of neutrophils in which Bcl-2 has been reported to inhibit apoptosis without affecting phagocytic clearance.

Apoptosis↗
PubMed1996

Induction of alpha/beta interferon and dependent nitric oxide synthesis during Chlamydia trachomatis infection of McCoy cells in the absence of exogenous cytokine.

The propensity of two Chlamydia trachomatis strains (L2/434/Bu [biovar LGV] and E/DK20/ON [biovar trachoma]) to induce putative host defense responses upon infection of McCoy (mouse) cell cultures was examined. Both strains induced production of alpha/beta interferon and nitric oxide (NO) by McCoy cells. NO synthesis was mediated by the inducible isoform of NO synthase as indicated by the ability of cycloheximide or the arginine analog NG-monomethyl-L-arginine to abolish NO production; the extent of the response was dependent upon the dose of chlamydiae applied. Incubation of McCoy cells with chloramphenicol prior to infection reduced NO production by strain 434 but not by DK20, suggesting that initial chlamydial metabolism was essential to induction by the LGV strain. Antibody inhibition studies indicated that NO synthesis was dependent upon production of alpha/beta interferon and induction via lipopolysaccharide. Overall, our findings show that chlamydiae are capable of the induction of interferon and NO in murine fibroblasts in the absence of exogenous cytokines. However, the role of NO as an antichlamydial effector could not be clearly demonstrated since treatment with an arginine analog, while suppressing NO production, gave no consistent enhancement of infected cell numbers.

Animals↗
PubMed1993

Low-nutrient induction of abnormal chlamydial development: a novel component of chlamydial pathogenesis?

The intracellular development of chlamydiae in McCoy cells incubated in Eagle's minimal essential medium lacking all 13 amino acids was examined both by fluorescence and electron microscopy and by infectivity titration. Aberrant development occurred in almost all inclusions of strains of Chlamydia trachomatis and C. psittaci with the production of abnormal forms which differed in size, shape and internal structure from normal reticulate and elementary body forms. Detailed analysis of the response of C. trachomatis L2 strain 434 to graded reductions in amino acid level showed that infectivity was reduced and morphological abnormality increased as amino acid concentrations were lowered from 33 to 0% of amino acids present in minimal essential medium. Reversion of inclusions to normal and reappearance of infectious forms occurred on restoration of amino acids and further incubation. It is suggested that aberrant development may account for the presence in vivo of non-cultivable chlamydiae and that such development can arise via tryptophan deprivation mediated by local release of interferon gamma.

Amino Acids↗
PubMedDate not supplied

Surgery for locally aggressive bone tumours.

Treatment of 16 patients with aggressive benign bone tumours and one patient with a low grade malignancy with a combined regimen of cryosurgery, phenolization and acrylic cementation is reported. Patients were aged between 9 and 51 years and were treated by this method between the years 1986 and 1993. Minimal follow up was 13 months. The commonest histological diagnosis was giant cell tumour (7), followed by aneurysmal bone cyst (6), chondromyxoidfibroma (3) and low grade chondrosarcoma (1). Patients were assessed for functional outcome and local recurrence. On average 86 per cent of premorbid function was restored at follow up and there was one local recurrence (6.29 per cent). We conclude that this is a satisfactory method of gaining local control of these tumours.

Adolescent↗