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Biomedical subjects

S A Bishop

Publications and source records attributed to S A Bishop.

17 recordsLinked to original sources
PubMed1999

Composite signalling from Serrate and Delta establishes leg segments in Drosophila through Notch.

The receptor protein NOTCH and its ligands SERRATE and DELTA are involved in many developmental processes in invertebrates and vertebrates alike. Here we show that the expression of the Serrate and Delta genes patterns the segments of the leg in Drosophila by a combination of their signalling activities. Coincident stripes of Serrate and Delta expressing cells activate Enhancer of split expression in adjacent cells through Notch signalling. These cells form a patterning boundary from which a putative secondary signal leads to the development of leg joints. Elsewhere in the tarsal segments, signalling by DELTA and NOTCH is necessary for the development of non-joint parts of the leg. We propose that these two effects result from different thresholds of NOTCH activation, which are translated into different downstream gene expression effects. We propose a general mechanism for creation of boundaries by Notch signalling.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Proximo-distal development in the legs of Drosophila.

The appendages of insects and vertebrates develop as extensions of the body wall. During development, a proximo-distal axis for growth and patterning is created in each appendage, in order to specify appendage length and allocation of pattern elements like joints and sensory organs. Here we use the expression of molecular markers to examine how PD development takes place in the legs of the fruit-fly Drosophila melanogaster. The data suggest a process of regionalization and progressive subdivision of an anlage similar to both insect embryonic segmentation and vertebrate somitogenesis.

Animals↗
PubMed1996

Vaginal and rectal infection of cats with feline immunodeficiency virus.

The objective of this study was to examine the potential of vaginal and rectal mucosal routes for feline immunodeficiency virus (FIV) uptake and infection, as a model of mucosal HIV infection, and to determine the fate of virus at these mucosal sites following transmission of infection. SPF cats were exposed to FIV isolates (PET, GL-8, T637), administered as either cell-associated or cell-free inocula, via the rectum or vagina. Establishment of infection was confirmed by isolation of infectious FIV from peripheral blood mononuclear cells (PBMC), and by presence of FIV proviral DNA in PBMC using a nested polymerase chain reaction. Fate of virus in tissue taken at necropsy from cats infected for 6-48 weeks was assessed by localizing FIV core and envelope proteins, p24 and gp41, using a biotin-streptavidin linked immunoperoxidase (IP) technique. Cells susceptible to infection were identified by an in situ hybridization technique for FIV viral DNA and RNA. Cell-free, as well as cell-associated, virus was infectious across intact vaginal and rectal mucosal surfaces. Transmission was most successful using cell-associated inocula, and via the rectal route. Cells infected with FIV were detected by IP staining in the colon of 6/9 rectally challenged cats and 1/5 vaginally challenged cats. Virus was predominantly localized within the epithelium at the base of the colonic crypts associated with lymphoid aggregates (follicle associated epithelium; FAE), and within the lymphoid follicle itself. Occasional infected cells were also noted within the lamina propria. The distribution of FIV DNA positive cells in the colon was similar to that for FIV antigen whilst FIV RNA positive cells were found more extensively, including within the lamina propria and lymphoid follicle. FIV infected cells were not detected within the vagina, or colonic and ileac lymph nodes. Similar patterns of infected cells were seen in all of the positive cats, indicating that colonic tissues remain persistently actively infected with FIV. We conclude that the FIV/cat model of rectal and vaginal mucosal infection should prove useful for characterizing the mechanism by which HIV infects mucosal surfaces and as a challenge system for the design of vaccines effective at preventing HIV infection via rectal and vaginal routes.

Animals↗
PubMed1996

Vaccination with fixed feline immunodeficiency virus (FIV) infected cells: protection, breakthrough and specificity of response.

Infection of cats with feline immunodeficiency virus (FIV), a naturally occurring lentivirus infection of cats which causes an AIDS-like disease, has generated considerable interest as an animal model for HIV vaccination. This paper reports on experiments performed to examine the potential of a fixed infected cell vaccine to confer protection against intraperitoneal challenge with cell-free FIV. The cell vaccine was highly immunogenic and elicited antibody responses to virus core antigen, p24, high virus neutralizing (VN) antibody titres, and antibodies which recognized cellular components of the vaccine. Whilst protection, assessed by the inability to detect infectious virus by virus isolation or polymerase chain reaction, against homologous but not heterologous FIV isolates was apparent up to week 12 post-challenge, when cats were monitored longer up to week 50 post-challenge a breakthrough in vaccine protection against homologous virus was observed. Protection could not be correlated with levels of antibody to p24 or VN antibody titres. In contrast with simian immunodeficiency virus vaccine studies in macaques there was no clear evidence that antibodies recognizing cellular components of the vaccine, including MHC class I and II antigens, conferred any protective effect following challenge. These results indicate that long-term post-challenge monitoring for infection is essential in lentivirus vaccine trials.

Animals↗
PubMed1994

The wingless signalling pathway and the patterning of the wing margin in Drosophila.

The margin of the wing of Drosophila is defined and patterned from a stripe of cells expressing the wingless (wg) gene that is established during the third larval instar in the developing wing blade. The expression of the genes cut and achaete in a small domain in the prospective wing margin region reflects the activity of wg and probably mediate its function. Our results indicate that, in the wing margin, the wingless signal requires the activity of at least three genes: armadillo (arm), dishevelled (dsh) and shaggy (sgg) and that the functional relationship between these genes and wg is the same as that which exist during the patterning of the larval epidermis. These observations indicate that arm, dsh and sgg encode elements of a unique 'wingless signalling pathway' that is used several times throughout development.

Animals↗
PubMed1993

Protein kinase C is required for light adaptation in Drosophila photoreceptors.

Protein kinase C (PKC) is a key enzyme for many cellular processes but its physiological roles are poorly understood. An excellent opportunity to investigate the function of PKC has been provided by the identification of an eye-specific PKC in Drosophila and a null PKC mutant, inaCP209 (refs 5,6). Bright conditioning lights delivered to inaC photoreceptors lead to an abnormal loss of sensitivity in whole cell recordings from dissociated ommatidia; this has been interpreted as 'hyper-adaptation' and PKC's role has been suggested to be distinct from light adaptation. A presumably related finding is that during intense light, the response of inaC declines to baseline. Invertebrate photoreceptors use the phosphoinositide signalling cascade, responding to single photons with so-called quantum bumps which sum to form the macroscopic response to light. Light adaptation allows photoreceptors to adjust their sensitivity over the enormous range of ambient intensities. Although the molecular mechanism of light adaptation remains obscure, it is a negative-feedback process mediated by a rise in cytosolic calcium and a decrease in bump size. We now show that under physiological conditions light adaptation is severely reduced in inaC, suggesting that eye-specific PKC, itself activated by a rise in cytosolic calcium and diacylglycerol, is required for adaptation. Furthermore, we show that in the absence of PKC individual bumps fail to terminate normally, an effect that can account for the pleiotropic manifestations of the inaC phenotype.

Adaptation, Ocular↗
PubMed1993

Programmed cell death (apoptosis) as a mechanism of cell death in peripheral blood mononuclear cells from cats infected with feline immunodeficiency virus (FIV).

FIV is a lentivirus infection of cats which induces an immunodeficiency syndrome associated with early qualitative defects in antigen-specific T cell function and with late quantitative defects in CD4+ T lymphocytes. We have observed that peripheral blood mononuclear cells (PBMC) from FIV-infected cats have impaired survival in culture. The mechanism of this in vitro dysfunction and depletion is not known. We have proposed that inappropriate induction of programmed cell death (apoptosis) could account for these in vitro defects. Here, we report that PBMC from FIV-infected cats, with impaired T cell blastogenesis and impaired survival in vitro, undergo an active cell death upon culture, which has the morphological and biochemical characteristics of programmed cell death (PCD). Apoptosis occurred in all six asymptomatic FIV-infected cats, and in none of the nine uninfected cats, which were studied. Changes in cell morphology under both light and electron microscopy, and fragmentation of genomic DNA were characteristic for apoptosing cells. Cell death was spontaneous and occurred in the absence of any stimuli, and culture with the T cell mitogen, concanavalin A (Con A), did not significantly enhance cell death. Activation-induced cell death was inhibited, in a dose-dependent manner, by addition to the incubation medium of zinc, which has been shown to inhibit the action of endonuclease responsible for the characteristic fragmentation of DNA. Since apoptosis has recently been implicated in AIDS pathogenesis, FIV infection may prove useful to study this aspect of retroviral, in particular HIV, infection.

Animals↗
PubMed1992

Experimental proliferative glomerulonephritis in the cat.

A model of chronic serum sickness was used to induce immune-complex glomerulonephritis in seven experimental cats, by daily intravenous inoculation of an increasing dose (5 to 35 mg) of human serum albumin (HSA). At week four, two of the seven animals developed anterior uveitis. At week 23, two different animals developed the subcutaneous oedema characteristic of the nephrotic syndrome (NS), whilst the other five cats appeared clinically normal. The kidneys were examined at necropsy by light microscopy and by transmission electron microscopy. The glomeruli of four animals (three with both proteinuria and uraemia, and one with proteinuria only) showed morphological changes under light microscopy. The abnormalities suggested that a diffuse mesangial proliferative glomerulonephritis (GN) had been induced in three cats and diffuse membranoproliferative GN induced in another. Ultrastructural studies revealed electron-dense deposits (immune-complexes) in six of the seven cats. Two cats without glomerular abnormalities by light microscopy had mesangial deposits and three cats with mesangial proliferative GN had deposits at mesangial, subendothelial and/or subepithelial sites. The single cat with membranoproliferative GN had deposits at mesangial, subendothelial, subepithelial and intramembranous sites. Immunohistological examination (peroxidase-antiperoxidase technique) showed that HSA and immunoglobulin (IgG and IgM) were deposited in the glomeruli of these cats. Deposits were the most dense in cats with more severe renal lesions. Deposits of IgM were most abundant. An extensive cellular infiltrate, comprising macrophages, neutrophils and plasma cells, was observed only in the four animals which showed abnormalities in glomerular ultrastructure. The disease induced in these cats thus appears to differ from the membranous nephropathy previously described in the cat and bears a close resemblance to immune complex (IC) disease in man. In view of the relatively few specific animal models of IC-mediated proliferative GN, this model has potential for application to the study of human IC disease.

Animals↗
PubMed1992

Antibody response and antibody affinity maturation in cats with experimental proliferative immune complex glomerulonephritis.

An experimental model of proliferative glomerulonephritis (GN) in the cat, which closely resembles human proliferative forms of GN, has been used to study the role of antibody and antibody affinity in the development of immune complex-mediated renal disease. The serum IgG and IgM antibody response to antigen, average antibody affinity (avidity) and affinity heterogeneity of the IgG and IgM populations was assessed at varying times after commencement of chronic immunization with the antigen, human serum albumin (HSA), by enzyme immunoassay. Cats could be classified according to whether they were "low", "intermediate" or "high" IgG responders, by quantification of serum IgG values. Cats with the lowest serum IgG values failed to develop glomerulonephritis. However, there was no relationship between actual IgG values and the severity of the induced disease. In contrast to IgG, there was no division of cats into low or high IgM anti-HSA responders. Again, cats with the lowest IgM values failed to develop GN, but, more interestingly, a late, marked increase in serum IgM anti-HSA occurred only in cats that developed clinical signs of GN (anterior uveitis and nephrotic syndrome). Maturation of average, functional IgG affinity (avidity) for HSA following chronic immunization was clearly demonstrated for all cats. At the end of the experiment, all cats had IgG of high affinity for HSA and the average affinity heterogeneity of the IgG populations was less than in measurements taken earlier. Values of IgG affinity at the end of the experiment were very similar both in cats which developed GN and in those which remained clinically, biochemically and pathologically normal. In contrast to IgG antibody, some cats developed IgM of increased affinity, whilst others produced antibody of reduced affinity, following chronic immunization. There was no correlation between the development of disease and the production of either low or high affinity IgM antibody. Data indicated that an alteration in IgM affinity occurred at a late stage, as serum IgM levels increased, in cats which progressed to develop GN. These findings suggested that an increase in both serum IgG and IgM anti-HSA values, in particular IgM, was associated with the development of a more severe immune complex renal disease in these cats. Although there was no evidence that differences in the average affinity of either the IgG or IgM antibody populations for HSA, were associated with the development of disease, the increase in IgM values was also accompanied by a concomitant alteration in IgM affinity for antigen.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Impaired T-cell priming and proliferation in cats infected with feline immunodeficiency virus.

OBJECTIVE: Cats naturally infected with feline immunodeficiency virus (FIV) are particularly susceptible to infection with opportunistic pathogens, suggesting that these animals are unable to develop an effective immune response against the pathogen. Previous studies have used CD4+:CD8+ lymphocyte ratios and mitogen blastogenesis to identify immunological abnormalities in FIV-infected cats. However, these studies provide limited information for understanding the nature of the cellular dysfunction in FIV-infected cats, particularly defects in antigen-specific immune responses. DESIGN: To investigate whether cats infected with FIV are less able to mount an immune response to previously unencountered antigens, we compared the development of antigen-specific cellular immunity at the stage of T-cell priming in uninfected and FIV-infected cats. INTERVENTIONS: The general immune status of cats was assessed by peripheral blood CD4+:CD8+ lymphocyte ratios (flow cytometry), and by lymphocyte blastogenesis response to T- and B-cell mitogens. In addition, we describe the development of an autologous culture system to measure specific priming of naive feline T-cells to soluble antigen in vitro. This assay was used to compare T-cell priming in uninfected cats and cats which had been infected with FIV for 6-27 months. RESULTS: As in HIV infection, CD4+:CD8+ lymphocyte ratios in FIV-infected cats were found to be inverted, due to a reduction in the percentage of CD4+ cells. In addition, lymphocyte blastogenesis to both T- and B-cell mitogens was significantly impaired in FIV-infected cats. Priming to keyhole limpet haemocyanin (KLH) elicited a late proliferative response resulting from the expansion of CD4+ (T-helper cells). T-cell growth factor secretion correlated with cell proliferation. Restimulation of cells with fresh antigen-presenting cells and antigen showed that antigen-specific T-cell priming had occurred in the initial culture. When primary proliferation responses in FIV-infected cats were examined, it was observed that naive CD4+ T-cells from FIV-infected cats were significantly impaired (P less than 0.001) in their ability to be primed to KLH when compared with uninfected controls. CONCLUSIONS: Impaired priming of naive CD4+ T-helper cells to antigen in FIV-infected cats may explain the increased susceptibility of these animals to infection by opportunistic pathogens. The poor ability of human patients with AIDS to develop humoral immunity following vaccination may also be caused by such a defect in T-cell priming.

Acquired Immunodeficiency Syndrome↗
PubMed1992

An early defect in primary and secondary T cell responses in asymptomatic cats during acute feline immunodeficiency virus (FIV) infection.

As in HIV infection of humans, cats infected with FIV are particularly susceptible to secondary infection by opportunistic pathogens, suggesting an impaired ability to elicit an effective immune response against foreign antigens. In order to investigate the development of immunity in FIV-infected cats, we have used an autologous culture system to directly measure priming of naive CD4+ T cells to soluble protein antigen, in vitro. Using this assay, we showed previously that cats infected with FIV for several months had significantly reduced primary proliferative responses. We have now examined cats before infection, and at varying times after infection with FIV, to determine how soon after infection this defect in T cell priming was evident, compared with other quantitative and qualitative measurements of lymphocyte function. Our results showed a progressive decline in immune function in asymptomatic cats during the acute stage of infection with FIV. Primary T cell responses were most sensitive and a significant reduction in proliferation of naive T cells to foreign antigen occurred 5 weeks after infection, despite normal blastogenesis to T cell mitogens and normal CD4+/CD8+ ratios at these times. Whilst lymphocyte proliferation to T cell mitogens was unaffected throughout, a significant reduction in proliferation to a B cell mitogen occurred from week 8 onwards. CD4+/CD8+ ratios fell significantly from week 13 onwards, and proliferation of the memory T cell population to a recall antigen was significantly impaired later, from week 19 onwards. The defect in the priming of naive T cells to foreign antigen early after infection may be important in determining susceptibility to secondary infections.

Animals↗
PubMed1991

Herpes simplex virus infection and damage in the central nervous system: immunomodulation with adjuvant, cyclophosphamide and cyclosporin A.

The role of the immune system in damage to the central nervous system (CNS) following infection with herpes simplex virus (HSV) was studied with the use of immune adjuvants and immunosuppressive drugs. The incidence of paralysis was found to be influenced significantly by the immune status of the animal. Thus, cyclosporin A (CsA) reduced the incidence of ear paralysis following inoculation of the pinna with virus, whilst cyclophosphamide (CY) increased the incidence of hind limb paralysis following i.v. inoculation with virus. Non-specific immunopotentiation with complete Freund's adjuvant (CFA) increased the incidence of hind limb paralysis. The inclusion of CNS antigen (mouse spinal cord homogenate) with the adjuvant enhanced the effect of adjuvant alone. The findings suggest that regulation of the immune response in the CNS may be of importance in the control of HSV-induced neuropathology.

Adjuvants, Immunologic↗
PubMed1991

Plasma and urine biochemical changes in cats with experimental immune complex glomerulonephritis.

Biochemical changes in plasma and urine were monitored in six cats before and during the induction of immune complex-mediated glomerulonephritis (ICGN) by daily intravenous administration of human serum albumin (HSA). The earliest indication of renal dysfunction in the cats was hypoalbuminaemia, which occurred as early as 13 weeks before cats developed clinical signs of renal disease. Proteinuria occurred 2 to 3 weeks before clinical disease, but was sensitive in predicting renal pathology in two cats that did not develop clinical signs of disease. In addition, increased activities of several urinary enzymes were detected in affected cats, with measurement of N-acetyl-beta-D-glucosaminidase and gamma-glutamyl transferase providing the earliest and most sensitive indication of renal damage. These plasma and urine measurements correlated more closely with the renal pathology, observed at postmortem, than clinical assessment of disease. It was concluded that ICGN in the cat could be diagnosed earliest by measurement of plasma protein concentration, whilst disease progress could be effectively monitored by including assays to measure urine protein and urine enzymes.

Animals↗
PubMed1989

Herpes simplex virus infection and damage in the central nervous system: immune response to myelin basic protein.

Two models of herpes simplex virus (HSV) infection in the mouse (inoculation of the ear pinna or intravenous inoculation) were used to assess immune responses to the virus and myelin basic protein (MBP). In both models demyelination in the central nervous system (CNS) can be assessed by clinical signs; ear paralysis (ear inoculation) and hind limb paralysis (intravenous inoculation). In the ear model, low levels of antibody to MBP were detected at 7 and 14 days after inoculation. The incidence of such antibody was low and bore no correlation with signs of paralysis. Cells from draining lymph nodes of mice inoculated in the pinna showed a proliferative response to HSV and MBP in vitro. In both models, delayed-type hypersensitivity reactions were demonstrated against HSV and MBP but such reactions were most significant after i.v. inoculation. This may reflect the greater CNS damage associated with hind limb paralysis.

Animals↗