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Biomedical subjects

J D Pollard

Publications and source records attributed to J D Pollard.

At least 55 records · Page 3Linked to original sources
PubMed1995

Intraneural activated T cells cause focal breakdown of the blood-nerve barrier.

Experiments were conducted to investigate the effect of activated T cells on the blood-nerve barrier (BNB) in experimental allergic neuritis (EAN). T cells reactive to the P2 component of myelin (P2 T cells) and known to cause EAN were injected into the sciatic nerve of Lewis rats. Animals were then given daily intraperitoneal (i.p.) injections of serum with known demyelinating activity (rabbit EAN serum) or control serum. Serial nerve conduction studies across the injected segment were performed and nerves were removed at various stages for histology. Focal conduction block and perivascular demyelination were evidence in T cell injected nerves of animals treated with EAN serum. In animals treated with control serum no conduction block was seen and only perivascular infiltrates without demyelination were present. Similar results were obtained with T cells reactive to non-neural antigens, although the effect was less marked. Systemically administered rabbit immunoglobulin (Ig) was demonstrated within the endoneurium of P2 T cell injected nerves by immunofluorescence and the endoneurial blood vessels showed increased permeability to circulating horseradish peroxidase (HRP). These findings demonstrate that activated T cells cause focal breakdown of the BNB, allowing circulating antimyelin antibody to enter the endoneurium with consequent focal demyelination. P2 reactive EAN producing T cells do not cause significant demyelination when injected intraneurally (i.n.) in the absence of circulating antimyelin antibody. Intraneural injection of tumour necrosis factor alpha (TNF-alpha) yielded similar results, causing conduction block and perivascular demyelination in the presence of circulating antimyelin antibody but not in control serum treated animals.

Animals↗
PubMed1995

Peripheral neuropathy associated with simvastatin.

Four patients are described who developed sensorimotor neuropathy while being treated with simvastatin and had complete or partial resolution of clinical abnormalities after withdrawal of treatment. In one case onset was within days of commencing treatment, but in two cases symptoms did not develop for two years. The electrophysiological and pathological features of the neuropathy were those of axonal degeneration. Clinical evidence of proximal and distal weakness and muscle fasciculations and persistent abnormalities of sensory conduction after recovery suggest the possibility of toxic damage to anterior horn cells and dorsal root ganglia. Thirty eight other cases with symptoms suggestive of peripheral neuropathy have been reported to the Australian Adverse Drug Reactions Advisory Committee, 22 of whom recovered after cessation of treatment; in five cases there was recurrence after re-exposure to the drug. Simvastatin should be considered among the causes of peripheral neuropathy, and the drug should be withdrawn if patients receiving it develop muscle weakness or sensory disturbances.

Adult↗
PubMed1994

A method for the isolation and culture of rat peripheral nerve vascular endothelial cells.

In studying autoimmune diseases of the human peripheral nervous system (PNS), in vitro studies involving the use of cultured rat Schwann cells, neurons, and disease-inducing immune system cells have provided basic information about disease pathogenesis. For example, T-cells that induce experimental allergic neuritis have been shown in vitro to damage Schwann cells, the target cell in these diseases. However, before making contact with Schwann cells, these T-cells must first pass through the blood-nerve barrier. Despite the importance of this interaction, no studies employing PNS endothelial cells in coculture with dorsal root ganglia cells to mimic the environment of the blood-nerve barrier have been reported. This paper describes a simple method for the isolation and culture of peripheral nerve vascular endothelial cells from adult rats that should facilitate in vitro studies of the blood-nerve barrier. Endothelial cells were identified by their expression of an endothelial cell marker, Factor VIII/von Willebrand factor. Their identity was further confirmed by their inability to express Thy 1.1, a fibroblast marker, and their in vitro morphology. Purity of endothelial cell cultures was ensured by a regular program of Thy 1.1 complement depletion of fibroblasts.

Animals↗
PubMed1994

Transfer of experimental allergic neuritis by intra neural injection of sensitized lymphocytes.

The final mediators of immune injury in EAN were investigated by intraneural injection of sensitized lymphocytes. Unfractionated specifically sensitized cells caused conduction block which was evident within 24 h after injection, reached significance within 3 days and remained depressed for over 12 days. Pathological changes at the site of injection showed infiltrating lymphoid and mononuclear cells and significant demyelination. The latter was only evident several days after the electrophysiological changes. These effects were shown to be specific, as injection of LNC from normal rats or those immunized with CFA alone did not induce the changes. Fractionation of sensitized LNC into the CD4+ and CD8+ subsets of T-cells showed only the former caused a drop in the amplitude ratio of nerve conduction. These changes in conduction were comparable to those observed in rats immunized with myelin/CFA to induce active EAN. Cyclosporin A (CSA) was given to host animals to block production of cytokines by the injected cells. This inhibited macrophage accumulation at the site of injection, but did not stop the electrophysiological changes. This result suggested that there was direct T-cell damage rather than damage consequent upon macrophage activation. These studies developed a model in which the cellular and molecular mechanisms of conduction block and demyelination in EAN can be studied by direct injection of specifically sensitized LNC.

Animals↗
PubMed1994

An electrophysiological and histological study of trypsin induced demyelination.

Ten-microliters quantities of trypsin or saline were injected into rat tibial nerve and the physiological and histological changes evaluated and compared to the focal demyelinating lesions induced by intraneural injection of rabbit EAN serum and proteinase K. The injection of trypsin produced progressive conduction block that was maximal on day 4, and a slowing of motor nerve conduction. Early retraction of myelin at paranodes, vesicular change, and macrophage stripping of myelin from nerve axons were seen on histological examination. At day 4, the first groups of completely demyelinated axons were seen, typically in a perivascular distribution. These changes were similar to those seen in the positive controls and thus support the postulate that proteolytic enzymes from macrophages--the dominant cellular species within the demyelinating lesion, play a central role in degradation of the myelin sheath in demyelinating diseases.

Animals↗
PubMed1994

A frame shift mutation in the PMP22 gene in hereditary neuropathy with liability to pressure palsies.

Hereditary neuropathy with liability to pressure palsies (HNPP) has been a associated with a deletion of 1.5 megabases of chromosome 17p. One of four biopsy proven HNPP families that we have studied did not possess this deletion. As the deleted DNA region includes the coding region for a peripheral myelin gene (PMP22), we used single strand conformation analysis to examine this gene for mutations in the non-deleted HNPP family. An abnormal fragment in exon 1 was identified, and sequencing revealed a two base pair deletion in all affected family members. The deletion results in a frame shift, providing strong evidence that this gene has an important role in the pathogenesis of the disease.

Base Sequence↗
PubMed1993

IgG monoclonal paraproteinaemia and peripheral neuropathy.

Five patients with peripheral neuropathy and benign IgG monoclonal paraproteinemia are reported, all of whom had a sensorimotor neuropathy with a remitting and relapsing course. The serum paraprotein level did not correlate with the patient's clinical status. Electrophsyiological studies showed marked slowing of conduction velocity and conduction block in four of the patients and mild slowing in the other. Sural nerve biopsies demonstrated a demyelinating neuropathy with inflammatory cell infiltrates in each of the five patients. Three of the patients had evidence of myelin/Schwann cell reactivity on immunofluorescence studies and in all nerves dense expression of major histocompatability complex class I and II molecules was evident within the endoneurium, on invading mononuclear cells, endothelial cells and Schwann cells. All the patients responded to treatment, plasmapheresis being particularly effective. Four patients have achieved prolonged remissions after all treatment had ceased. These five cases of peripheral neuropathy and IgG paraproteinaemia were identical in their clinical, electrophysiological and pathological features to patients with chronic inflammatory demyelinating polyneuropathy.

Adult↗
PubMed1992

Immunosuppression in nerve allografting: is it desirable?

Immunologically incompatible sciatic nerve grafts were inserted into the severed sciatic nerves of Wistar rats. In an attempt to induce graft tolerance, low-dose cyclosporin A (CsA) was administered to some animals for 20 weeks, then gradually withdrawn. Behavioural, electrophysiological and histological studies indicated that some degree of regeneration took place in all animals regardless of treatment. Neither a daily dose of 5 mg/kg nor 10 mg/kg was sufficient to prevent the rejection and subsequent disruption of allograft structure, and as a consequence reinnervation of the distal stump was limited. This was manifest both in the poor functional recovery of the denervated foot, and in the large number of regenerated axons found outside of the perineurial membranes of the transplanted fascicles. Therefore, tolerance was not induced at these doses. Furthermore, the significant decrease in the amplitude of electromyographs recorded from experimental and unoperated (control) animals suggests CsA may have a deleterious effect on unlesioned nerve even at these low doses. It would be prudent, therefore, to exercise caution in the combined use of nerve allografts and CsA immunosuppression, until the neurotoxicity of CsA has been investigated further. This is particularly important since CsA is sometimes used in the treatment of certain neuropathic autoimmune diseases.

Action Potentials↗
PubMed1992

Peripheral nervous system demyelination from systemic transfer of experimental allergic neuritis serum.

The ability of systemically transferred experimental allergic neuritis (EAN) serum to produce EAN lesions in recipient animals was studied. Seventeen Lewis rats received five daily 1-ml intraperitoneal (i.p.) injections of sera from rabbits with EAN induced with bovine myelin/complete Freund's adjuvant (CFA). Another 17 rats received similar injections of sera from rabbits inoculated with CFA alone. On day 0 (the first day of i.p. injections), all rats were injected in the proximal tibial branch of the right sciatic nerve with a single 10-microliters injection of 0.03 M 5-hydroxytryptamine (5-HT) in sterile 0.15 M saline. Proximal tibial branches of left sciatic nerves received similar single injections of saline alone. Animals were then studied using electrophysiological and histological techniques. In all animals, intraneural saline injection had no significant effect upon nerve conduction. In the presence of circulating CFA serum, 5-HT injection caused a mild gradual decrease in amplitude ratio becoming maximal by day 17 (P < 0.005) and partially resolving by day 28. In contrast, in the presence of circulating EAN serum, 5-HT injection caused a more rapid and severe decrease in amplitude ratio becoming maximal by days 6-10 (P < 0.001 day 6; P < 0.0001 day 10) and completely resolving by day 28. Histological analysis of nerves injected with 5-HT in CFA serum-treated animals showed areas of mild demyelination, axonal degeneration and some fibre loss consistent with needle trauma. In contrast, 5-HT-injected nerves in animals administered EAN serum showed areas of marked cellular infiltration and severe demyelination in association with numerous debris-filled infiltrating cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Interactions between CD4+ T-cells and rat Schwann cells in vitro. 1. Antigen presentation by Lewis rat Schwann cells to P2-specific CD4+ T-cell lines.

Interactions between CD4+ P2-specific T-cell lines and Schwann cells were examined in vitro by scanning electron microscopy (SEM) and T-cell proliferation studies. CD4+ T-cell lines clustered around and attached to Schwann cells which expressed Major histocompatibility complex (MHC) class II molecules. Only those P2-specific T-cell lines capable of inducing experimental allergic neuritis (EAN) when injected into adult Lewis rats clustered around the Schwann cells. T-cell lines responsive to P2 but not able to induce EAN did not cluster around Schwann cells. The addition of exogenous P2 protein inhibited in a dose-dependent way clustering and proliferation of the P2-specific T-cell lines. Cytoplasmic P2 was detected in Schwann cells by immunofluorescent labelling and the results of proliferation assays in this study suggest that endogenous P2 protein was processed by the Schwann cells and presented to T-cell lines in association with MHC class II molecules. The clustering and proliferation of class II-restricted CD4+ P2-specific T-cell lines in the presence of Schwann cells provides evidence for a role for Schwann cells as facultative antigen presenting cells, processing and presenting 'self' endogenous antigen to CD4+ T-cell lines capable of inducing EAN.

Animals↗
PubMed1992

Interactions between CD4+ T-cells and rat Schwann cells in vitro. 2. Cytotoxic effects of P2-specific CD4+ T-cell lines on Lewis rat Schwann cells.

The cytotoxic effects of CD4+ P2-specific T-cell lines on Schwann cells were examined in vitro with 51Cr-release cytotoxicity assays. Only those P2-specific T-cell lines capable of inducing EAN when injected back into adult Lewis rats were cytotoxic to the Schwann cells. The addition of exogenous P2 protein was not necessary for the cytotoxic effect. The monoclonal antibody (mAb) OX6 directed against Major histocompatibility complex (MHC) class II molecules blocked cytotoxicity, indicating an essential role for MHC class II molecules in this interaction between CD4+ T-cell lines and Schwann cells.

Animals↗
PubMed1992

Patterns of conduction impairment in experimental allergic neuritis. An electrophysiological and histological study.

Electrophysiological and histological studies of peripheral nerve were performed in 24 Lewis rats with experimental allergic neuritis (EAN) in which disease had been induced by a single myelin and adjuvant inoculation in one footpad. Demyelination was demonstrated in transverse nerve sections from ventral roots, proximal sciatic nerves and also in distal plantar nerves. Histological and electrophysiological assessments showed that injected limbs were more affected than uninjected limbs. Neurophysiological studies demonstrated two distinct patterns of conduction failure based upon proximal/distal compound muscle action potential (CMAP) amplitude ratios in both uninjected and injected limbs. Slightly more than half of all nerve trunks showed a mildly reduced distal CMAP amplitude irrespective of stimulus origin. The rest displayed a more severe reduction of distal amplitude that was length-dependent, becoming smaller with proximal stimulation. Histological lesions in plantar nerves were often more severe than those in proximal sciatic nerves or ventral roots. Axonal degeneration was an uncommon finding. This study has demonstrated patterns of peripheral nerve conduction impairment similar to those reported in patients with inflammatory demyelinating neuropathy. Moreover, it has shown that a low distal CMAP amplitude may result from demyelination of distal motor nerve segments and not necessarily from axonal degeneration.

Animals↗
PubMed1991

Interferon-gamma inhibition suppresses experimental allergic neuritis: modulation of major histocompatibility complex expression of Schwann cells in vitro.

This study examines the modulation of major histocompatibility complex (MHC) expression on Lewis rat Schwann cells (Scs) cultured in the presence of dorsal root ganglion neurons (DRG). MHC class I and II molecules were induced on Scs using recombinant murine interferon-gamma (IFN-gamma), lymph node cells (LNC), removed at day 9 from Lewis rats with experimental allergic neuritis (EAN) and syngeneic T-cell line cells responsive to P2 basic protein. EAN LNC induced MHC class I on Scs but only IFN-gamma or P2-responsive T-cells induced MHC class II. Control LNC from animals injected with Freund's adjuvant alone or naive spleen cells did not induce MHC class II. P2 T-cells clustered in aggregates to the Scs. Similar studies were performed with inhibitors of IFN-gamma; hydrocortisone, cyclosporin A, dibutyryl cyclic AMP, methyl-xanthine and prostaglandin E2. Each agent produced a dose-dependent inhibition of MHC expression and prevented clustering of P2-responsive T-cells to Scs.

Animals↗
PubMed1991

Vasculitic neuropathy. A clinical and pathological study.

The clinical, electrophysiological and pathological features and prognosis of 34 patients with peripheral neuropathy caused by necrotizing vasculitis were evaluated. The causes included polyarteritis nodosa and its Churg-Strauss variant, rheumatoid arthritis, undifferentiated connective tissue disease, Wegener's granulomatosis, primary Sjögren's disease, and chronic lymphocytic leukaemia with cryoglobulinaemia; 2 patients had no evidence of systemic vasculitis. Mononeuritis multiplex was the most common clinical manifestation, followed by asymmetrical polyneuropathy and distal symmetrical polyneuropathy. Pain was a frequent symptom. Nerve conduction studies were abnormal in all cases, and in 3 patients there was conduction block or severe slowing of motor conduction. Necrotizing vasculitis was present in sural nerve biopsies of most cases, and severe active axonal degeneration was a dominant feature. Immunofluorescent staining of blood vessels for immunoglobulin, C3 and fibrinogen was positive in all cases in which it was performed, even when there was no cellular infiltration. All patients were treated with prednisone alone or in combination with other immunosuppressive agents, or with plasmapheresis. Long-term follow-up studies demonstrated that although the peripheral neuropathy usually improved and caused only mild to moderate functional disability, the long-term prognosis of the systemic disease was poor with a 5-yr survival of only 37%.

Adult↗
PubMed1990

Low dose, short term cyclosporin A does not protect the Schwann cells of allogeneic nerve grafts.

The question of whether Cyclosporin A, at the low doses reported to allow survival of nerve allografts, allows the allogeneic Schwann cells to survive has been investigated. Nerve allografts were inserted by microsurgical techniques into trembler mice treated with 10 mg/kg or 15 mg/kg Cyclosporin A, daily for 12 weeks post-operatively. Electrophysiological recordings were made one week prior to surgery, and at the end of the immunosuppression period, after which the grafts were processed for electron microscopy. All grafts showed signs of rejection and donor Schwann cells had been replaced by host cells. The results suggest that Cyclosporin A in these doses is insufficient to overcome rejection problems or to induce tolerance to donor Schwann cells.

Action Potentials↗
PubMed1990

Rat and human Schwann cells in vitro can synthesize and express MHC molecules.

The expression of MHC class I and II molecules on cultured rat and human Schwann cells (SCs) was studied to determine whether these molecules could be synthesized by SCs in the absence of T cells. Normal rat and human SCs in vitro expressed low levels of class I MHC, but this was markedly increased by incubation with interferon gamma (IFN-gamma). Untreated SCs of rat or human origin did not express detectable class II MHC molecules, but after 48 hours incubation with IFN-gamma 100 U/ml, 20% of rat SCs and 90% of human SCs were class II positive. Immunoelectron microscopy confirmed the surface expression of MHC molecules on SCs and demonstrated class II MHC within endocytotic vesicles. These findings provide further evidence for an immunological role for SCs as antigen presenting cells or as targets for cytotoxic T cells.

Animals↗