Biomedical subjects

F Mackay

Publications and source records attributed to F Mackay.

30 records · Page 2Linked to original sources

PubMed1996

Signaling through the lymphotoxin beta receptor induces the death of some adenocarcinoma tumor lines.

Surface lymphotoxin (LT) is a heteromeric complex of LT-alpha and LT-beta chains that binds to the LT-beta receptor (LT-beta-R), a member of the tumor necrosis factor (TNF) family of receptors. The biological function of this receptor-ligand system is poorly characterized. Since signaling through other members of this receptor family can induce cell death, e.g., the TNF and Fas receptors, it is important to determine if similar signaling events can be communicated via the LT-beta-R. A soluble form of the surface complex was produced by coexpression of LT-alpha and a converted form of LT-beta wherein the normally type II LT-beta membrane protein was changed to a type I secreted form. Recombinant LT-alpha 1/beta 2 was cytotoxic to the human adenocarcinoma cell lines HT-29, WiDr, MDA-MB-468, and HT-3 when added with the synergizing agent interferon (IFN) gamma. When immobilized on a plastic surface, anti-LT-beta-R monoclonal antibodies (mAbs) induced the death of these cells, demonstrating direct signaling via the LT-beta-R. Anti-LT-beta-R mAbs were also identified that inhibited ligand-induced cell death, whereas others were found to potentiate the activity of the ligand when added in solution. The human WiDr adenocarcinoma line forms solid tumors in immunocompromised mice, and treatment with an anti-LT-beta-R antibody combined with human IFN-gamma arrested tumor growth. The delineation of a biological signaling event mediated by the LT-beta-R opens a window for further studies on its immunological role, and furthermore, activation of the LT-beta-R may have an application in tumor therapy.

Adenocarcinoma↗

PubMed1994

Differential responses of fibroblasts from wild-type and TNF-R55-deficient mice to mouse and human TNF-alpha activation.

The role of the two TNF receptor types, TNF-R55 and TNF-R75, was studied on mouse fibroblasts, taking advantage of TNF-R55-deficient mice generated by gene targeting (Tnfr1 degree-mice), and selectivity of human TNF-alpha for mouse TNF-R55. Radioligand binding assays showed that both TNF receptors were expressed on wild-type mouse fibroblasts, whereas normal levels of TNF-R75 were expressed on mouse fibroblasts isolated from Tnfr1 degree-mice. It was found that TNF-R55 controlled four major TNF-induced fibroblast functions: (1) adhesion to leukocyte cell lines as well as ICAM-1, VCAM-1, CD44, and MHC class I up-regulation; (2) secretion of other cytokines as demonstrated by stimulated IL-6 and granulocyte-macrophage-CSF releases; (3) cell proliferation; and (4) NF-kappa B activation. Stimulation through TNF-R75, in TNF-R55-deficient fibroblasts, did not have any effect in these functions. In general, mouse TNF-alpha (recognizing both mouse TNF receptors) had a higher sp. act. than human TNF-alpha (recognizing only mouse TNF-R55) in wild-type fibroblasts, whereas both mouse and human TNF-alpha had similar cytotoxic activities in WEHI 164 cells.

Animals↗

PubMed1994

Dentofacial form in the five-year-old child with unilateral cleft lip and palate.

It is generally believed that studies of outcome for children with clefts of the lip and palate should be based on patients who are in their teens. This means that health care workers who look after these children would have to wait many years until the quality of treatment could be evaluated. In this study, significant differences between two centers, Oslo and Manchester, in facial form at the age of 5 years were detected. Based on cephalometric analysis, children from Manchester were more likely to have a retrognathic maxilla with the upper lip significantly behind the esthetic plane. An important future step may be the setting up of "reference centers" with a large archive of database information for each racial group. This would assist smaller centers in comparing their outcomes.

Age Factors↗

PubMed1994

Phenotypic analysis of TNFR1-deficient mice and characterization of TNFR1-deficient fibroblasts in vitro.

In order to analyse the physiological relevance of the 55 kDa tumor necrosis factor receptor 1 (TNFR1) and its role in various TNF related pathological conditions, such as septic shock, we have generated mice by gene targeting deficient for TNFR1 expression. The TNFR1-deficient mice are unable to cope with Listeria monocytogenes infections but mount an apparently normal immune response when challenged with Vaccinia or LCMV viruses. They are resistant to the lethal effects of lipopolysaccharide (LPS) after sensitization with D-galactosamine (D-GalN) but remain sensitive to very high doses of LPS given alone. We have analyzed functions relevant to inflammatory processes, such as adhesion, secondary factor release, and proliferation in fibroblasts derived from these mice. We show that the TNFR1 virtually monopolises TNF-mediated signaling in all these situations and that the 75 kDa TNFR2 seems to be largely restricted to an accessory role, which is compatible with the previously established "ligand passing" hypothesis.

Alleles↗

PubMed1993

Human tumor necrosis factor alpha (TNF alpha) mutants with exclusive specificity for the 55-kDa or 75-kDa TNF receptors.

To probe the ligand receptor interface, a number of point mutations were introduced in selected regions of human tumor necrosis factor (TNF) alpha by site-directed mutagenesis. The mutated proteins were expressed in Escherichia coli and analyzed for selective binding to recombinant 55- and 75-kDa TNF receptors in competition with radiolabeled wild-type TNF alpha. Generally, mutations in the loop from position 29 to 34 and at positions 86 and 146 preferentially impaired binding to the 75-kDa TNF receptor, whereas mutations in the region from 143 to 145 mainly affected binding to the 55-kDa TNF receptor. Mutation of the conserved Tyr87 resulted in a dramatic loss of binding activity to both receptors. The selectivity for one or the other receptor type was found to be enhanced by combining two or three point mutations, the effects of the single mutations with respect to receptor selectivity being at least additive. A combination of the mutations Arg32-->Trp and Ser86-->Thr yielded a double mutant (R32W-S86T) with wild-type binding to the 55 kDa, but no measurable binding to the 75-kDa TNF receptor. In contrast, combining the Asp143-->Asn and Ala145-->Arg mutations (D143N-A145R) resulted in a complete loss of binding to the 55-kDa TNF receptor, whereas binding to the 75-kDa TNF receptor was impaired by only 5-10-fold. In functional assays, selective activation of the 55-kDa TNF receptor by the R32W-S86T mutant elicited a full cytotoxic response in human KYM-1 cells and secretion of interleukin 6 and granulocyte-macrophate colony-stimulating factor in human umbilical vein endothelial cells. In contrast, stimulation of the 75-kDa TNF receptor with the D143N-A145R mutant as well as with agonistic antibodies failed to induce these responses.

Animals↗

PubMed1993

Tumor necrosis factor alpha (TNF-alpha)-induced cell adhesion to human endothelial cells is under dominant control of one TNF receptor type, TNF-R55.

Tumor necrosis factor alpha (TNF-alpha) is a pleiotropic cytokine triggering cell responses through two distinct membrane receptors. Stimulation of leukocyte adhesion to the endothelium is one of the many TNF-alpha activities and is explained by the upregulation of adhesion molecules on the endothelial cell surface. Human umbilical vein endothelial cells (HUVEC) were isolated, cultured, and demonstrated to express both TNF receptor types, TNF-R55 and TNF-R75. Cell adhesion to HUVEC was studied using the HL60, U937, and MOLT-4 cell lines. HUVEC were activated by either TNF-alpha, binding to both TNF-R55 and TNF-R75, and by receptor type-specific agonists, binding exclusively to TNF-R55 or to TNF-R75. The TNF-alpha-induced cell adhesion to HUVEC was found to be controlled almost exclusively by TNF-R55. This finding correlated with the exclusive activity of TNF-R55 in the TNF-alpha-dependent regulation of the expression of the intercellular adhesion molecule type 1 (ICAM-1), E-selectin, and vascular cell adhesion molecule type 1 (VCAM-1). The CD44 adhesion molecule in HUVEC was also found to be upregulated through TNF-R55. However, both TNF-R55 and TNF-R75 upregulate alpha 2 integrin expression in HUVEC. The predominant role of TNF-R55 in TNF-alpha-induced adhesion in HUVEC may correlate with its specific control of NF-kappa B activation, since kappa B elements are known to be present in ICAM-1, E-selectin, and VCAM-1 gene regulatory sequences.

Base Sequence↗

PubMed1992

Craniofacial form in class III cases.

Lateral skull cephalograms from 50 patients who subsequently had surgical correction of their Class III malocclusion were analysed using a complete linkage cluster analysis based on skull shape. Five subgroups were identified and are described. All subjects had a degree of mandibular prognathism while only 14 per cent had maxillary retrognathism. An increased lower face height was found in 58 per cent.

Adult↗

PubMed1992

The effect of adhesive type and thickness on bond strength of orthodontic brackets.

Fine-mesh based brackets were bonded to plastic cylinders using four different adhesives. Adhesive thickness was controlled using a bonding jig. The bond was then tested to failure using a shear force. Each adhesive had its own minimum thickness, probably related to its viscosity. Increasing the thickness of the adhesiveness to 0.26 mm, using a stainless steel spacer had minimal effect on their mean shear bond strength.

Acrylic Resins↗

PubMed1991

First steps in audit.

The results of two audit projects carried out in a District Orthodontic Unit are described. Although prospective data collection was the goal, it was found that this method yielded little information as the data collection forms were poorly filled in. The main problem was a lack of definition of terms and inadequate discussion between clinical and clerical staff. A retrospective audit using five clearly defined fields was more successful. It is very important that there is provision to verify the data collected. The time commitment for clinical staff should not be underestimated.

Data Collection↗

PubMed1991

Reliability of cephalometric analysis using manual and interactive computer methods.

This study compares the results of cephalometric analyses using manual and interactive computer graphics methods. Results are statistically in favour of the interactive computer system. This study provides a basis for ongoing research into alternative methods of cephalometric analyses, such as digitization and automatic landmark identification using sophisticated computer vision systems.

Cephalometry↗

PubMed1988

Food poisoning in hospitals in Scotland, 1978-87.

During the 10-year period 1978-87 there were 48 outbreaks of food poisoning in Scottish hospitals affecting a total of 2287 persons of whom 12 died. This compared with 50 outbreaks during the previous 5 years (1973-77) when over 1500 persons and 7 deaths were recorded. Although the incidence of outbreaks has decreased the average number of persons affected in outbreaks has increased. A marked reduction was seen in the incidence of outbreaks due to Clostridium perfringens, in contrast to foodborne salmonellosis which remains a problem. Thirty-four hospitals, of which 10 reported two or more outbreaks, were involved. The type of hospitals most frequently affected were general (14), psychiatric (13), geriatric (9) and hospitals for the mentally subnormal (7). Meat, including poultry meat, was incriminated in over 90% of outbreaks where a food vehicle was identified. In modern or re-equipped kitchens cooking in advance with subsequent reheating is being progressively discontinued as more food is being cooked on the day of consumption, a practice which may readily explain the decreasing incidence of outbreaks due to Cl. perfringens. Bacterial cross-contamination from poultry-meat and other raw foods, compounded by inadequate temperature control, however, continues to be a problem in some hospitals. It is too early as yet to determine whether the removal of Crown immunity will have any effect on the future incidence of hospital 'food poisoning'.

Campylobacter↗

PubMedDate not supplied

Proinflammatory responses are efficiently induced by homotrimeric but not heterotrimeric lymphotoxin ligands.

The cytokine, lymphotoxin [LT, tumor necrosis factor beta (TNF beta)] is a potent mediator of proinflammatory and tumoricidal activities. Soluble lymphotoxin is a complex of three LT alpha chains. Its receptors, TNF-R55 and TNF-R75, bind in clefts formed by adjacent identical LT alpha monomers. LT also exists as membrane anchored heterotrimers comprised of LT alpha and LT beta chains. The major and minor membrane forms, LT alpha 1 beta 2 and LT alpha 2 beta 1, respectively, bind a unique receptor, LT beta-R. As LT alpha 2 beta 1 expresses an LT alpha-alpha cleft, it also binds TNF-R. In this report we have compared the effects of ligand engagement of TNF-R and LT beta-R by evaluating the ability of soluble LT alpha beta complexes to initiate activities of human umbilical vein endothelial cells which are characteristically signalled by TNF. We recently reported that soluble LT alpha 1 beta 2 signals via LT beta-R to mediate cytotoxicity of a subset of gamma interferon (IFN-gamma) treated carcinomas. We now show that human LT alpha beta heterotrimers do not efficiently activate LT beta-R+, TNF-R+ human endothelial cells in vitro and only inefficiently mediates lethal toxicity in mice. We also show that neither LT alpha beta heterotrimer signals via TNF-R; in fact LT alpha 2 beta 1 trimers fail to activate NF-kappa B and rather inhibit ligand-induced TNF-R signalling supporting the role for aggregation in TNF-R signalling. Thus, the ability of LT alpha beta complexes to efficiently initiate tumoricidal but not inflammatory activities distinguishes the LT/LT beta-R from the LT/TNF-R pathways and suggest novel strategies for exploiting the LT ligands in tumor therapy and for inhibiting TNF-R-mediated inflammatory sequellae.

Animals↗