Biomedical subjects

K Ratcliffe

Publications and source records attributed to K Ratcliffe.

5 recordsLinked to original sources

PubMed2001

Refugee services. Hosts with the most.

More than 1,500 asylum seekers have registered with a specialist support scheme set up by a primary care trust. It is staffed by primary health professionals and holds walk-in clinics two mornings a week. The scheme helps asylum seekers find GPs and advises on housing problems. Staff have found some of the work harrowing. The government should make extra provision for pregnant asylum seekers who cannot breast feed because they are HIV-positive.

Community Health Centers↗

PubMed2000

CD14 employs hydrophilic regions to "capture" lipopolysaccharides.

CD14 participates in the host innate inflammatory response to bacterial LPS obtained from Escherichia coli and other Gram-negative bacteria. Evidence from several laboratories suggests that different regions of the amino-terminal portion of the molecule may be involved in LPS binding. In this report a series of single-residue serine replacement and charge reversal mutations were generated to further elucidate the mechanism by which this protein may bind a multitude of different LPS ligands. Single-residue CD14 mutation proteins were examined for their ability to bind LPS obtained from E. coli, Porphyromonas gingivalis, and Helicobacter pylori and facilitate the activation of E-selectin from human endothelial cells. In addition, the single-residue CD14 mutation proteins were employed to perform monoclonal epitope-mapping studies with three LPS-blocking Abs that bound tertiary epitopes. Evidence that several different hydrophilic regions of the amino-terminal region of CD14 are involved in LPS binding was obtained. Epitope-mapping studies revealed that these hydrophilic regions are located on one side of the protein surface. These studies suggest that CD14 employs a charged surface in a manor similar to the macrophage scavenger receptor to "capture" LPS ligands and "present" them to other components of the innate host defense system.

Amino Acid Sequence↗

PubMed1997

Identification of CD14 residues involved in specific lipopolysaccharide recognition.

CD14 is a key molecule responsible for the innate host inflammatory response to microbial infection. It is able to bind a wide variety of microbial ligands and facilitate the activation of both myeloid and nonmyeloid cells. However, its specific contribution to the innate recognition of bacteria is not known. Presently there is no information on the contribution of individual CD14 residues to Escherichia coli lipopolysaccharide (LPS) binding or on the molecular basis of the interaction between CD14 and LPS from other bacteria. LPS obtained from Porphyromonas gingivalis, a bacterium associated with chronic inflammatory disease, binds CD14 and activates myeloid cells but does not facilitate the activation of nonmyeloid cells. The transfer and binding of these two LPS species to soluble CD14 recombinant globulin proteins with single point mutations was examined. Functional activity of the mutant proteins was monitored by E-selectin expression on human umbilical cord endothelial cells. The analysis identified a charge reversal mutation in a single residue, E47, that demonstrated selective binding to E. coli LPS but not to P. gingivalis LPS. E-selectin activation assays indicated that proteins with mutations at position E47 maintained their structural integrity. Other mutations, including a charge reversal mutation of residue E58, did not significantly reduce the binding of either LPS ligand or the ability of the molecule to facilitate E-selectin activation. These data demonstrate that CD14 can selectively recognize different LPS ligands.

Amino Acid Sequence↗

PubMed1996

Helicobacter pylori and Porphyromonas gingivalis lipopolysaccharides are poorly transferred to recombinant soluble CD14.

Helicobacter pylori and Porphyromonas gingivalis are gram-negative bacteria associated with chronic inflammatory diseases. These bacteria possess lipopolysaccharides (LPSs) that are able to activate human monocytes to produce tumor necrosis factor alpha but fail to activate human endothelial cells to express E-selectin. With Escherichia coli LPS, tumor necrosis factor alpha activation requires membrane-bound CD14 and E-selectin expression requires soluble CD14 (sCD14). Therefore, the ability of H. pylori and P. gingivalis LPSs to transfer to and bind sCD14 was examined by using immobilized recombinant sCD14 and human serum or recombinant LPS-binding protein (LBP). H. pylori and P. gingivalis LPSs were transferred to sCD14 when serum or LBP was present. However, the transfer of these LPSs to CD14 in serum was significantly slower than the transfer of E. coli LPS. Quantitation of the transfer rates by Michaelis-Menten kinetics yielded K(m) values of 6 and 0.1 nM for H. pylori and E. coli LPSs, respectively. The amount of P. gingivalis LPS required to obtain half-maximum binding to CD14 was approximately 10-fold greater than the amount of E. coli LPS required. The slower transfer rates displayed by these LPSs can be explained by the poor binding to LBP observed in direct binding assays. These results are consistent with the proportionately lower ability of these LPSs to activate monocytes compared with E. coli LPS. However, the ability of H. pylori and P. gingivalis LPSs to bind LBP and transfer to sCD14 demonstrates that the lack of endothelial cell CD14-dependent cell activation by these LPSs occurs distal to sCD14 binding.

Acute-Phase Proteins↗

PubMed1995

Ability of bacteria associated with chronic inflammatory disease to stimulate E-selectin expression and promote neutrophil adhesion.

Porphyromonas gingivalis, Pseudomonas aeruginosa, and Helicobacter pylori have been shown to be associated with adult periodontal disease, chronic lung infections, and peptic ulcers, respectively. The ability of these bacteria to stimulate E-selectin expression and promote neutrophil adhesion, two components necessary for the recruitment of leukocytes in response to infection, was investigated. Little or no stimulation of E-selectin expression was observed with either P. gingivalis or H. pylori when whole cells, lipopolysaccharide (LPS), or cell wall preparations added to human umbilical cord vein endothelial cells were examined. P. aeruginosa was able to induce E-selectin to near-maximal levels; however, it required approximately 100 to 1,000 times more whole cells or LPS than that required by E. coli. Neutrophil-binding assays revealed that LPS and cell wall preparations obtained from these bacteria did not promote endothelial cell adhesiveness by E-selectin-independent mechanisms. In addition, P. gingivalis LPS blocked E-selectin expression by LPS obtained from other bacteria. We propose that lack of E-selectin stimulation and the inability to promote endothelial cell adhesiveness are two additional indications of low biologically reactive LPS. We suggest that this property of LPS may contribute to host tissue colonization. In addition, the ability of P. gingivalis to inhibit E-selectin expression may represent a new virulence factor for this organism.

Bacterial Infections↗