Search PubMed⌕ Search

Biomedical subjects

D R Greaves

Publications and source records attributed to D R Greaves.

At least 37 records · Page 2Linked to original sources
PubMed1998

Immunohistochemical evidence for a macrophage scavenger receptor in Mato cells and reactive microglia of ischemia and Alzheimer's disease.

Macrophage scavenger receptors (MSR) are implicated in the development of atherosclerosis and amyloid b-protein deposition in Alzheimer's disease. However, histopathological studies of MSR expression in human tissues have been hampered by a lack of specific antibodies. Using MSR-deficient mice, we successfully raised a novel monoclonal antibody against human MSR together with high-titer antisera. These antibodies specifically recognized human tissue macrophages and human MSR protein purified from differentiated THP1 cells. In normal brain, MSR staining was mainly distributed to the perivascular cells, which correspond to Mato's fluorescent granular perithelial cells (Mato cells). In the lesions of ischemia and Alzheimer's disease, a subset of microglia stained positive for MSR. These novel antibodies are useful tools for analysis of MSR expression in human tissues.

Alzheimer Disease↗
PubMed1998

Recent progress in defining the role of scavenger receptors in lipid transport, atherosclerosis and host defence.

Scavenger receptors bind and internalize modified lipoproteins. There are several different classes of scavenger receptors in mammalian cells and their relative contribution to lipid transport in normal physiology and pathological conditions such as atherosclerosis has been the subject of intense investigation. Mice with a disruption in the macrophage scavenger receptor SR-A gene exhibit a reduced size of atherosclerotic lesions and also exhibit an enhanced susceptibility to pathogens and endotoxic shock. In addition to their role in lipid transport, scavenger receptors play important roles in host defence and in the regulation of acquired immunity. Recent progress in delineating the mechanisms by which oxidized LDL effects changes in gene expression will be reviewed.

Animals↗
PubMed1998

A naturally occurring isoform of the human macrophage scavenger receptor (SR-A) gene generated by alternative splicing blocks modified LDL uptake.

The class A macrophage scavenger receptors (SR-A) are macrophage-specific trimeric integral membrane glycoproteins that have been implicated in many macrophage-associated physiological and pathological processes including atherosclerosis, Alzheimer's disease, and host defense. There are two forms of the receptor that have been previously cloned, and both are generated by alternative splicing of a single gene. Here we report the cloning of a third, alternatively spliced isoform of the human SR-A gene (type III hSR-A). The novel isoform is expressed in the human monocytic leukemia cell line THP-1 and also in primary human monocyte derived macrophages. When expressed in CHO-K1 cells, type III hSR-A does not internalize AcLDL despite having the domain shown to mediate this function in type I and II hSR-A. We show that type III protein has altered intracellular processing and is trapped within the endoplasmic reticulum, making it unable to perform endocytosis. Type III protein acts as a dominant negative isoform by reducing modified LDL uptake in CHO cells stably expressing either type I or type II SR-A. The demonstration that a naturally occurring splice variant of SR-A mRNA can act as a dominant negative isoform suggests a novel mechanism for regulation of scavenger receptor activity in macrophages.

Alternative Splicing↗
PubMed1997

CCR6, a CC chemokine receptor that interacts with macrophage inflammatory protein 3alpha and is highly expressed in human dendritic cells.

Dendritic cells initiate immune responses by ferrying antigen from the tissues to the lymphoid organs for presentation to lymphocytes. Little is known about the molecular mechanisms underlying this migratory behavior. We have identified a chemokine receptor which appears to be selectively expressed in human dendritic cells derived from CD34+ cord blood precursors, but not in dendritic cells derived from peripheral blood monocytes. When stably expressed as a recombinant protein in a variety of host cell backgrounds, the receptor shows a strong interaction with only one chemokine among 25 tested: the recently reported CC chemokine macrophage inflammatory protein 3alpha. Thus, we have designated this receptor as the CC chemokine receptor 6. The cloning and characterization of a dendritic cell CC chemokine receptor suggests a role for chemokines in the control of the migration of dendritic cells and the regulation of dendritic cell function in immunity and infection.

Amino Acid Sequence↗
PubMed1997

A new class of membrane-bound chemokine with a CX3C motif.

Chemokines direct the trafficking of white blood cells in immune surveillance, playing a key role in inflammatory and infectious diseases such as AIDS. All chemokines studied so far are secreted proteins of relative molecular mass approximately 7K-15K and fall into three families that are defined by a cysteine signature motif: CXC, CC and C (refs 3, 6, 7), where C is a cysteine and X any amino-acid residue. We report here the identification and characterization of a fourth human chemokine type, derived from non-haemopoietic cells and bearing a new CX3C fingerprint. Unlike other chemokine types, the polypeptide chain of the human CX3C chemokine is predicted to be part of a 373-amino-acid protein that carries the chemokine domain on top of an extended mucin-like stalk. This molecule can exist in two forms: either membrane-anchored or as a shed 95K glycoprotein. The soluble CX3C chemokine has potent chemoattractant activity for T cells and monocytes, and the cell-surface-bound protein, which is induced on activated primary endothelial cells, promotes strong adhesion of those leukocytes. The structure, biochemical features, tissue distribution and chromosomal localization of CX3C chemokine all indicate that it represents a unique class of chemokine that may constitute part of the molecular control of leukocyte traffic at the endothelium.

Amino Acid Sequence↗
PubMed1996

The human lysozyme promoter directs reporter gene expression to activated myelomonocytic cells in transgenic mice.

The 5' region of the human lysozyme gene from -3500 to +25 was fused to a chloramphenicol acetyltransferase (CAT) reporter gene and three transgenic founder mice were obtained. All three transgenic lines showed the same pattern of CAT enzyme expression in adult mouse tissues that was consistent with the targeting of elicited, activated macrophages in tissues and developing and elicited granulocytes. In normal mice high CAT enzyme activity was found in the spleen, lung, and thymus, tissues rich in phagocytically active cells, but not in many other tissues, such as the gut and muscle, which contain resident macrophages. Cultured resident peritoneal macrophages and cells elicited 18 hr (granulocytes) and 4 days (macrophages) after injection of sterile thioglycollate broth expressed CAT activity. Bacillus Calmette-Guérin infection of transgenic mice resulted in CAT enzyme expression in the liver, which contained macrophage-rich granulomas, whereas the liver of uninfected mice did not have any detectable CAT enzyme activity. Although the Paneth cells of the small intestine in both human and mouse produce lysozyme, the CAT gene, under the control of the human lysozyme promoter, was not expressed in the mouse small intestine. These results indicate that the human lysozyme promoter region may be used to direct expression of genes to activated mouse myeloid cells.

Animals↗
PubMed1995

Tissue-specific targeting of cytokine unresponsiveness in transgenic mice.

The ubiquitous cellular distribution of certain cytokine receptors has hampered attempts to define the physiologically important cell-specific functions of cytokines in vivo. Herein, we report the generation of transgenic mice that express a dominant-negative IFN gamma receptor alpha chain mutant under the control of either the human lysozyme promoter or the murine lck proximal promoter, which display tissue-specific unresponsiveness in the macrophage or T cell compartments, respectively, to the pleiotropic cytokine, IFN gamma. We utilize these mice to identify previously undefined cellular targets of IFN gamma action in the development of a murine antimicrobial response and the mixed lymphocyte reaction. Moreover, we identify the macrophage as a critical responsive cell in manifesting the effects of IFN gamma in regulating CD4+ T helper subset development. These studies thus represent a novel approach to studying the cell-specific actions of an endogenously produced pleiotropic cytokine in vivo.

Animals↗
PubMed1991

Globin gene switching: a paradigm or what?

The delineation of the beta-globin locus control region has led to a new understanding of the developmental regulation of the beta-globin gene cluster. It now seems that globin gene switching is effected through the sequential and mutually exclusive interaction of the locus control region with the embryonic, fetal and adult stage specific globin genes.

Animals↗