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Biomedical subjects

B P Morgan

Publications and source records attributed to B P Morgan.

At least 19 recordsLinked to original sources
PubMed1992

Meningococcal septicaemia in a C6-deficient patient and effects of plasma transfusion on lipopolysaccharide release.

Patients whose blood is deficient in the terminal component of complement have an increased susceptibility to meningococcal infection. However, mortality from meningococcal infection is lower in these patients than in immunocompetent subjects. We studied a C6-deficient patient with meningococcal sepsis who received fresh frozen plasma (FFP). The patient's initial plasma endotoxin, C6, and terminal-complement-complex concentrations were low, but rose sharply after treatment with FFP. Samples of the patient's serum taken shortly after admission did not cause endotoxin release from Escherichia coli J5 in vitro, but endotoxin-releasing activity was restored in serum samples taken after infusion of FFP. It is possible that C6-deficient patients have reduced mortality from meningococcal infection because their serum cannot cause acute release of endotoxin from the invading organism and extensive tissue damage is thus avoided.

Adult↗
PubMed1992

Antithyroid drugs and release of inflammatory mediators by complement-attacked thyroid cells.

Thyroid cells are exposed to complement attack in Graves' disease and Hashimoto's thyroiditis, but are resistant to killing by homologous complement. We have examined the effects of sublethal complement attack on thyroid cells in vitro. Extracellular reactive oxygen metabolites were produced and prostaglandin E2, interleukin-1 alpha, and interleukin-6 were released after complement attack. Cells pretreated with interferon-gamma and interleukin-1 alpha, which increase expression of CD59, were more resistant to these effects of complement. Conversely, blockade of CD59 with monoclonal antibody increased complement-mediated oxygen radical production and release of prostaglandin E2, interleukin-1 alpha, and interleukin-6. The antithyroid drugs methimazole and propylthiouracil abolished or reduced oxygen radical production by complement-attacked thyroid cells and reduced cytokine release. These results suggest that sublethal complement attack in autoimmune thyroid diseases exacerbates tissue injury by causing thyroid cells to release potent phlogistic mediators, although some degree of protection may be afforded in vivo by cytokine-mediated upregulation of CD59. Antithyroid drugs, concentrated within thyroid cells, will prevent the release of these inflammatory molecules, which may in turn explain the amelioration of thyroiditis and remission of Graves' disease after such treatment.

Antigens, CD↗
PubMed1992

Isolation and characterization of a membrane protein from rat erythrocytes which inhibits lysis by the membrane attack complex of rat complement.

The membrane attack complex (MAC) of complement in humans is regulated by several membrane-bound proteins; however, no such proteins have so far been described in other species. Here we report the isolation and characterization of a rat erythrocyte membrane glycoprotein of molecular mass 21 kDa which inserts into cell membranes and is a potent inhibitor of the rat MAC. This protein, here called rat inhibitory protein (RIP), was first partially purified by column chromatography from a butanol extract of rat erythrocyte membranes. Monoclonal antibodies (Mabs) were raised against RIP and used for its affinity purification. Affinity-purified RIP was shown to inhibit in a dose-dependent manner the cobra venom factor (CVF)-mediated 'reactive' lysis of guinea pig erythrocytes by rat complement. Conversely, the anti-RIP MAbs 6D1 and TH9 were shown to markedly enhance the CVF-mediated lysis of rat erythrocytes by rat complement. RIP acted late in the assembly of the MAC (at or after the C5b-8 stage) and was releasable from the membranes of rat erythrocytes by phosphatidylinositol-specific phospholipase C. These features, together with its size, deglycosylation pattern and N-terminal amino acid sequence, lead us to conclude that RIP is the rat homologue of the human MAC-inhibitory protein CD59 antigen.

Amino Acid Sequence↗
PubMed1992

Isolation and characterization of the complement-inhibiting protein CD59 antigen from platelet membranes.

Several groups have recently described the isolation of a 20 kDa membrane-attack-complex (MAC)-inhibiting protein, termed 'CD59 antigen', from human erythrocyte membranes. Antibodies raised against erythrocyte CD59 antigen detect antigen on the surface of many other cell types, and in some of these cells the antigen has been shown to have a molecular mass similar to that of the erythrocyte protein and to confer resistance to lysis by the MAC. A platelet-membrane form of CD59 antigen has been described and reported to be much larger than the erythrocyte protein. Here I report the isolation of CD59 antigen from platelet membranes and its molecular and functional characterization. The platelet protein is not significantly larger than the erythrocyte form and possesses similar MAC-inhibiting activity. Platelet CD59 antigen is anchored to the membrane via a glycosyl-phosphatidylinositol link, and consequently it is suggested that deficiency of this protein might be responsible for the increased thrombotic tendency observed in paroxysmal nocturnal haemoglobinuria.

Antigens, CD↗
PubMed1992

The role of calcium in rat oligodendrocyte injury and repair.

The role of intracellular calcium in oligodendrocyte injury is investigated using cultured rat oligodendrocytes. Calcium ionophores A23187 and ionomycin mimic both complement and perforin attack, causing oligodendrocyte lysis at concentrations which do not lyse other glia. Membrane vesiculation, the mechanism by which oligodendrocytes resist and recover from complement and perforin attack, is also induced by A23187. Oligodendrocytes are more susceptible to complement attack in the presence of a calmodulin inhibitor (W7), which also inhibits vesiculation. These results imply that calmodulin is involved in membrane repair from complement attack, and indicate that changes in intracellular calcium play an important yet paradoxical role in the oligodendrocyte response to injury, dictating both susceptibility and cellular recovery.

Animals↗
PubMed1992

Immunohistochemical determination of complement activation in joint tissues of patients with rheumatoid arthritis and osteoarthritis using neoantigen-specific monoclonal antibodies.

Murine monoclonal antibodies specific for neoepitopes expressed by C9 incorporated into membrane attack complexes and by membrane-bound C3b and iC3b have been prepared and characterised. These reagents were used to determine the extent and locus of complement activation in synovial-tissues obtained from patients with rheumatoid arthritis and osteoarthritis. In the four rheumatoid arthritis patients there was extensive deposition of C3 activation products and C5b-9 complexes onto the synovial membrane and the pattern of deposition of both neoantigens in serial tissue sections was very similar. There was less extensive staining for C3 and, particularly, C9 neoepitopes on the apical surface of vessel endothelia. In two of four osteoarthritic patients a similar pattern of C3 and C9 neoepitope deposition was found; in the remaining patients no C5b-9 could be located. Synovial vessel walls, but not synovial cells, from both groups of patients stained extensively for the complement regulatory protein CD59. In synovial membranes from patients with osteoarthritis, C9 appeared to be present predominantly in SC5b-9 complexes whereas in rheumatoid arthritis patients no evidence of S-protein incorporation into membrane attack complexes could be demonstrated, suggesting that in rheumatoid arthritis there is damage to the synovial membrane as a result of complement activation and C5b-9 deposition.

Adult↗
PubMed1992

Expression and function of membrane attack complex inhibitory proteins on thyroid follicular cells.

Human thyroid cells are resistant to lysis by the homologous membrane attack complex. By immunohistochemical staining we here show that normal thyroid cells and those in Graves' disease and Hashimoto's thyroiditis express two membrane attack complex-inhibiting proteins, CD59 antigen and membrane attack complex-inhibiting protein/homologous restriction factor (MIP/HRF). In vitro, the expression of both molecules was enhanced by interleukin-1 (IL-1), tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma) and cytokine-treated thyroid cells were more resistant to lysis by homologous complement. Blocking experiments with monoclonal antibodies against CD59 antigen and MIP/HRF showed that both molecules contributed but CD59 antigen was the more important in mediating resistance to complement attack. Expression of these proteins may be an important determinant of the severity of tissue injury produced by complement-fixing thyroid peroxidase antibodies in autoimmune thyroid disease.

Antigens, CD↗
PubMed1992

Membrane attack complex (MAC)-mediated damage to spermatozoa: protection of the cells by the presence on their membranes of MAC inhibitory proteins.

Although antibody and complement are known to cause immobilization and killing of spermatozoa in vitro the components of the complement system mediating these effects remain undefined. Here we have examined the effects of the membrane attack complex (MAC) on spermatozoa and demonstrate that spermatotoxic effects are dependent on assembly of the complete MAC. We subsequently examined the presence and functional significance of the complement regulatory proteins decay accelerating factor (DAF), MAC-inhibiting protein (MIP) and CD59 antigen on spermatozoa. Both DAF and CD59 antigen were present on the membranes of these cells. Neutralization of CD59 antigen with specific antibodies increased the susceptibility of the cells to MAC-mediated damage, suggesting a role for this molecule in the protection of spermatozoa from complement-mediated damage in the female reproductive tract.

Antigens, CD↗
PubMed1992

Characterization of the membrane attack complex inhibitory protein CD59 antigen on human amniotic cells and in amniotic fluid.

A functional complement system and the potential for its activation are present in human amniotic fluid. We have recently demonstrated that CD59 antigen is present and functionally active on human amniotic epithelial cells (HAEC). We have now further examined the role of this protein on HAEC and have also demonstrated its presence in amniotic fluid (AF). CD59 Ag on HAEC is similar in size to the erythrocyte protein and is anchored via glycosyl phosphatidylinositol. The AF protein retained the capacity to incorporate into target cells and protect against lysis by complement. These data suggest that HAEC secrete into AF a form of CD59 Ag which retains inhibitory activity and which may be important in protection of the foetus from maternal complement in utero.

Amnion↗
PubMed1992

Properties of a low molecular weight complement component C6 found in human subjects with subtotal C6 deficiency.

A sensitive ELISA assay was used to quantitate serum complement component C6 concentrations. Levels in the range 0.3-3 micrograms/ml were measured in samples from eight individuals (four separate pedigrees) and two subjects with subtotal combined C6/C7 deficiency who have been reported previously. We defined C6 levels in this range as subtotal C6 deficiency (C6SD). In contrast, C6 deficiency with levels below 0.03 micrograms/ml was defined as C6Q0. C6Q0 has been found in 29 unrelated cases which have already been reported. Investigations of the properties of the C6 found in the C6SD subjects showed it to be haemolytically active and able to incorporate into the terminal complement complex. The protein had a relative molecular weight (Mr) of approximately 86% of normal C6 and this Mr was identical to that of the C6 of one combined deficient subject. The Mr of the C6 of the other combined deficient subject was previously estimated as 79% of the Mr of normal C6. Isoelectric focusing (IEF) analysis with band development by haemolytic overlay revealed that all C6SD samples produced an identical weak C6 band pattern anodal to normal C6A bands. The C7 IEF patterns of the two combined deficient subjects were identical, and the C6 IEF patterns of both were identical to those of the C6SD subjects. Thus the C6 of the combined deficient subjects is probably the same abnormal protein found in the C6SD individuals. None of the C6SD or combined deficient subjects have had meningococcal disease and it may be that low C6 levels afford some protection.

Adult↗
PubMed1991

Killing of cells by perforin. Resistance to killing is not due to diminished binding of perforin to the cell membrane.

Different cell types vary widely in their susceptibility to killing by the pore-forming cytolytic molecule perforin. In particular, the cells responsible for synthesis of perforin, i.e. cytotoxic T lymphocytes (CTL) and natural killer (NK) cells, are very resistant to cytolysis by this molecule. It has previously been suggested that resistance is due, at least in part, to diminished binding of perforin to these cells. The purpose of the present study was to compare binding of perforin to sensitive and resistant cell types. To this end, perforin was biosynthetically labelled prior to purification. The purified labelled protein was then utilized to obtain a direct measure of the amount of perforin bound to cells during attack. Resistant cells (CTL, neutrophils) bound at least as much perforin as did sensitive cells (K562, HL60 etc.), indicating that resistance to perforin involves mechanisms operating after binding of the lytic molecule.

Animals↗
PubMed1991

Complement deficiency and disease.

Complement deficiency is associated with an increased prevalence of pyogenic infections and immune complex disease. The spectrum of disease in deficient individuals depends on the stage in the complement system at which the block in activation occurs. Here, Paul Morgan and Mark Walport review current knowledge of hereditary complement deficiencies in humans, emphasizing the importance of these 'experiments of nature' in defining the roles of complement in vivo.

Bacterial Infections↗
PubMed1991

Antibody-mediated demyelination in experimental allergic encephalomyelitis is independent of complement membrane attack complex formation.

The effects of decomplementation by cobra venom factor (CVF) on the pathogenesis of inflammation and demyelination in experimental allergic encephalomyelitis (EAE) and acute antibody-mediated demyelinating EAE (ADEAE) have been quantified histologically and immunocytochemically. In rats immunized with 50 micrograms of myelin basic protein in Freund's complete adjuvant containing 100 micrograms heat-killed Mycobacterium tuberculosis H37Ra, clinical signs of EAE were completely suppressed by two injections of CVF given 9 and 12 days post-immunization. Suppression of clinical disease was associated with a dramatic reduction in peri-vascular inflammation in the CNS, although immunohistochemical staining identified small numbers of infiltrating T cells and macrophages. In contrast, CVF treatment had no significant effect on the clinical severity of ADEAE and although C9 deposition within the CNS was virtually abolished, there was no statistically significant decrease in the extent of demyelination or inflammation. These observations indicate that in the absence of complement components C3 and C5 an antibody-dependent cell-mediated cytotoxic response plays an important role in the pathogenesis of antibody-mediated demyelination. The major role of the complement cascade in EAE appears to be the generation of pro-inflammatory factors that enhance the inflammatory response within the CNS in animals facing a mild encephalitogenic challenge.

Animals↗
PubMed1991

The complement-inhibiting protein, protectin (CD59 antigen), is present and functionally active on glomerular epithelial cells.

Protectin (CD59 antigen) is a 20-kD phosphatidyl-inositol-linked membrane protein that inhibits formation of the membrane attack complex (MAC) of complement on homologous cells. Although the antigen has been identified in a number of human tissues, until recently a functional role had been demonstrated only in circulating cells. Using immunofluorescence techniques we have shown the presence of protectin on human glomerular epithelial cells (GEC) in culture and on GEC, tubular epithelial cells and endothelial cells in frozen sections of normal human renal cortex. In addition, we present evidence that this protein functions in protection of GEC from homologous complement: cultured cells incubated with the Fab2 fragment of a monoclonal anti-protein antibody were markedly more susceptible to killing by homologous serum than were cells in the absence of Fab2 anti-protectin. These findings suggest that this protein may be important in the maintenance of glomerular integrity in vivo, and may be of relevance in certain renal diseases.

Animals↗
PubMed1991

Functionally active complement proteins C6 and C7 detected in C6- and C7-deficient individuals.

Two sensitive sandwich ELISAs based on monoclonal antibodies directed to native C6 and C7 allowed the detection and quantitation of these complement proteins in 20 out of 37 serum samples from individuals who had previously been classified as deficient in these proteins as assessed by immunochemical and/or functional assays. Furthermore, serum from four C6-deficient and one combined C6-/C7-deficient individual showed an increase in the terminal complement complex (TCC) and a decrease in native C6 and C7 after complement activation as assayed by specific ELISAs. Despite their (incomplete) deficiencies, these individuals therefore possess functionally active terminal complement proteins with respect to their ability to generate the TCC. As these individuals have no history of a susceptibility to neisserial infections, even low concentrations of functionally active C6 and C7 may provide sufficient protection against those micro-organisms whose destruction requires TCC formation.

Antibodies, Monoclonal↗
PubMed1991

Imaging Ca2+ changes in individual oligodendrocytes attacked by T-cell perforin.

Cytosolic-free calcium changes in cultured rat oligodendrocytes attacked with murine T-cell perforin were measured using digital image processing of fura-2-loaded cells. Permeability to the membrane impermeant dye, propidium iodide, and the ability to retain fura-2 were also assessed. Oligodendrocyte response to perforin attack was heterogeneous, ranging from small, transient increases in cytosolic calcium to rapid cell death. Changes in cytosolic calcium occurred in all cells and about half of the cells also became permeable to propidium iodide. Only a minority of these cells proceeded to lysis, as evidenced by loss of fura-2. The cytosolic-free calcium rises visualized here in single cells could initiate non-lethal effects, thereby disturbing oligodendrocyte function and synthesis and maintenance of myelin.

Animals↗
PubMed1991

Terminal complement complexes and C1/C1 inhibitor complexes in rheumatoid arthritis and other arthritic conditions.

Terminal complement complex (TCC) and C1r-C1s-C1 inhibitor complex (C1/C1 INH) concentrations were measured in plasma and synovial fluid from patients with arthritis and related to other measures of disease activity. Both TCC and C1/C1 INH concentrations were significantly increased in patients with rheumatoid arthritis (RA) compared with patients with osteoarthritis (plasma and synovial fluid, P less than 0.05) and normal subjects (plasma only, P less than 0.001). In the patients with RA, there was no correlation between plasma or synovial fluid TCC concentrations and IgM rheumatoid factor, immune complex or C1/C1 INH levels. However, in 10 patients with seronegative RA, C1/C1 INH and immune complex levels correlated significantly in synovial fluid (r = 0.69, P less than 0.05) although not in plasma (r = 0.52). Plasma and synovial fluid TCC and C1/C1 INH concentrations did not differ in rheumatoid patients with severe compared with mild joint disease (categorized by the Ritchie score). These results confirm a role for complement activation in RA but suggest that several mechanisms are involved in its pathogenesis.

Adult↗