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Peripheral neuropathies are associated with a variety of clinical symptoms ranging from motor and sensory symptoms to autonomic dysfunction. The primary disease causes for peripheral nerve disorders are also very heterogeneous, including genetic causes, inflammation mediated damage and physical trauma. A common theme in these neuropathies is the important contribution of the immune system; leading either to a deterioration or an amelioration of the disease. Immune responses are typically mediated by immune cells such as antigen-presenting cells, macrophages or T-cells. However, also non-immune cells such as microglia in the central nervous system or Schwann cells in the peripheral nervous system might play a key role in innate and adaptive immune responses. Just like microglia, Schwann cells express a plethora of pattern recognition receptors that allows them to recognize exogenous as well as endogenous danger signals. Upon activation, Schwann cells initiate and regulate local immune responses by presenting antigens and by secreting cytokines and chemokines, which will further attract immune cells to the site of injury. By interacting with immune cells they contribute in shaping immune responses that can lead to inflammatory neuropathies. In hereditary neuropathies, the immune system has also been shown to aggravate the disease phenotype. Besides, a neuroprotective role for the immune system has been recognized that becomes mainly prominent in cases of acute nerve injury. The present review focuses on the recently recognized immune competent role of Schwann cells and its involvement in peripheral neuropathies., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Human apolipoprotein E (apoE) is a 34.2kDa glycosylated protein with three isoforms (apoE2, apoE3 and apoE4). Experimental autoimmune neuritis (EAN), an animal model for human Guillain-Barré syndrome, is an immune-mediated experimental disorder of the peripheral nervous system (PNS). Increased susceptibility to EAN in apoE deficient mice has been previously found. To elucidate the isoform-dependent effects of apoE on EAN, we used human apoE2, E3 and E4 transgenic mice (Tg) immunized with P0 peptide 180-199, as well as T cell proliferation test, macrophage and Schwann cell (SC) cultures to investigate the effects of apoE isoforms on the functions of T cells, macrophages and SCs both under naïve conditions and in EAN. Clinical signs of EAN were most severe in wild type (WT) C57BL/6 mice and apoE4 Tg mice, followed by apoE2 Tg mice and apoE3 Tg mice (WT≈E4>E2>E3, p<0.01). At the nadir of EAN, spleen weight and lymphocyte proliferation were in line with the clinical severity of the disease. Proliferation tests of purified T cells from naive mice stimulated with phytohemagglutinin or interleukin-12 showed isoform-specific differences (WT≈E4>E3≈E2, p<0.01). Macrophages from both naïve and EAN mice produced nitric oxide upon inflammatory stimulation with lipopolysaccharide, interferon-γ, polyinosinic:polycytidylic acid or combinations thereof, in an isoform-dependent manner (WT≈E4>E2>E3, p<0.01). Generalized intervention with 1400W, a specific inducible nitric oxide synthase inhibitor, significantly suppressed the clinical course of EAN in apoE2, E3 and E4 Tg mice and in WT mice. During the recovery stage of disease, the highest expression of CD178 (FasL) on SCs was found in apoE3 Tg mice. Our data support an isoform-dependent effect of apoE on EAN. This might be due to the isoform-specific effects of apoE on functions of T cells, macrophages and SCs, which contribute to the distinct clinical courses of EAN. ApoE3 might not only inhibit the onset and suppress the clinical severity of EAN, but also enhance the termination of immune responses in the PNS., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Host Schwann cell (SC) migration into nerve allografts is the limiting factor in the duration of immunosuppression following peripheral nerve allotransplantation, and may be affected by different immunosuppressive regimens. Our objective was to compare SC migration patterns between clinical and experimental immunosuppression regimens both over time and at the harvest endpoint. Eighty mice that express GFP under the control of the Schwann cell specific S100 promoter were engrafted with allogeneic, nonfluorescent sciatic nerve grafts. Mice received immunosuppression with either tacrolimus (FK506), or experimental T-cell triple costimulation blockade (CSB), consisting of CTLA4-immunoglobulin fusion protein, anti-CD40 monoclonal antibody, and anti-inducible costimulator monoclonal antibody. Migration of GFP-expressing host SCs into wild-type allografts was assessed in vivo every 3 weeks until 15 weeks postoperatively, and explanted allografts were evaluated for immunohistochemical staining patterns to differentiate graft from host SCs. Immunosuppression with tacrolimus exhibited a plateau of SC migration, characterized by significant early migration (< 3 weeks) followed by a constant level of host SCs in the graft (15 weeks). At the endpoint, graft fluorescence was decreased relative to surrounding host nerve, and donor SCs persisted within the graft. CSB-treated mice displayed gradually increasing migration of host SCs into the graft, without the plateau noted in tacrolimus-treated mice, and also maintained a population of donor SCs at the 15-week endpoint. SC migration patterns are affected by immunosuppressant choice, particularly in the immediate postoperative period, and the use of a single treatment of CSB may allow for gradual population of nerve allografts with host SCs., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Schwann cells are the myelinating glia cells of the peripheral nervous system (PNS). In inflammatory neuropathies like the Guillain-Barré syndrome (GBS) Schwann cells become target of an autoimmune response, but may also modulate local inflammation. Here, we tested the functional relevance of Schwann cell derived MHC expression in an in vitro coculture system. Mouse Schwann cells activated proliferation of ovalbumin specific CD8+ T cells when ovalbumin protein or MHC class I restricted ovalbumin peptide (Ova(257-264) SIINFEKL) was added and after transfection with an ovalbumin coding vector. Schwann cells activated proliferation of ovalbumin specific CD4+ T cells in the presence of MHC class II restricted ovalbumin peptide (Ova(323-339) ISQAVHAAHAEINEAGR). CD4+ T-cell proliferation was not activated by ovalbumin protein or transfection with an ovalbumin coding vector. This indicates that Schwann cells express functionally active MHC class I and II molecules. In this study, however, Schwann cells lacked the ability to process exogenous antigen or cross-present endogenous antigen into the MHC class II presentation pathway. Thus, antigen presentation may be a pathological function of Schwann cells exacerbating nerve damage in inflammatory neuropathies.

Macrophages are critically involved in the pathogenesis of genetically caused demyelination, as it occurs in models for inherited demyelinating neuropathies. It is presently unknown which factors link the Schwann cell-based myelin mutation to the activation of endoneurial macrophages. Here we identified the chemokine monocyte chemoattractant protein-1 (MCP-1) as a first and crucial factor upregulated in Schwann cells of mice heterozygously deficient for the myelin protein zero. The chemokine could be identified as an important mediator of macrophage immigration into peripheral nerves. Furthermore, a 50% reduction of chemokine expression by crossbreeding with MCP-1-deficient mice reduced the increase in macrophage numbers in the mutant nerves and lead to a robust amelioration of pathology. Surprisingly, the complete absence of MCP-1 aggravated the disease. Our findings show that reducing but not eliminating chemokine expression can rescue genetically caused demyelination that may be an interesting target in treating demyelinating diseases of the peripheral nervous system.

Matrix metalloproteinase-9 (MMP-9) is an extracellular protease that is induced hours after injury to peripheral nerve. This study shows that MMP-9 gene deletion and neutralization with MMP-9 antibody reduce macrophage content in injured wild-type nerves. In mice with delayed Wallerian degeneration (WldS), MMP-9 and tumor necrosis factor alpha (TNFalpha) decline in association with the reduced macrophage recruitment to injured nerve that characterizes this strain of mice. We further determined that TNFalpha acts as an MMP-9 inducer by establishing increased MMP-9 levels after TNFalpha injection in rat sciatic nerve in vivo and primary Schwann cells in vitro. We found reduced MMP-9 expression in crushed TNFalpha knockout nerves that was rescued with exogenous TNFalpha. Finally, local application of MMP-9 on TNFalpha-/- nerves increased macrophage recruitment to the lesion. These data suggest that TNFalpha lies upstream of MMP-9 in the pathway of macrophage recruitment to injured peripheral nerve.

In vitro cultivation of human corneal endothelial cells (HCEC) is associated with loss of typical cobblestone-like appearance during successive passages. Thus far morphology was the sole criterion for the cell's endothelial nature. Mouse monoclonal antibodies (mabs) to human corneal endothelial cells were raised using standard immunization and hybridoma isolation procedures. The specificity of mabs for human corneal endothelial cells was tested in comparison to other endothelial cell types, to fibroblasts, corneal keratocytes and to human retinal pigmented epithelial cells. In addition immunofluorescence or immunoperoxidase staining was performed with frozen tissue sections of human corneas and with various other human tissues. The mab 9.3.E reacts with cultured human corneal endothelial cells, but not with cultured human fibroblasts and human keratocytes. In frozen sections selective positivity of corneal endothelium in contrast to negativity of the other corneal cell types was confirmed. In investigated extraocular tissues positivity was observed in smooth muscle cells including related cells (i.e. Ito and mesangial cells) and in Schwann's cells and adipocytes, but apparently not in vascular endothelial cells. The mab is human-specific and binds to a protein with a molecular weight of 130 kDa mainly accumulating along cell membranes. A mouse monoclonal antibody against human corneal endothelial cells was established in vitro and was shown to be capable of differentiating corneal endothelial cells from other corneal cell types, especially from corneal keratocytes. It is, however, not cornea-specific, but also reacts with certain extraocular cell types., (Copyright 2001 Academic Press.)

We have developed a method for isolating Schwann cells (SC) from human fetal peripheral nerve and maintaining these SC in vitro under serum-free conditions. This method yields essentially pure SC which have a bipolar, spindle-shaped morphology; align in fascicles; and express typical glial cell markers. Human fetal SC can be maintained for months under serum-free conditions with the neuregulin NDF beta. These human fetal SC can mimic axonal contact in vivo by retaining the functional capacity to strongly associate with neurites of cultured human fetal dorsal root ganglia. These isolation, culture, and coculture techniques provide a method for investigating SC-neuron interactions as well as development and function of human fetal SC.

Sciatic nerves were excised from 3 beagle dogs about 5 h after their sacrifice, treated three times by freezing and thawing, and stored in physiological saline for 3 months at -20 degrees C until used. Nerve segments 5 cm in length prepared from these stored nerves were transplanted to the common peroneal nerve in the right hindlimb of beagle dogs. Sixteen beagle dogs in total were used, in four treatment groups of two pairs each studied at 1 and 3 months. Five-hundred microliters basic fibroblast growth factor (bFGF) of two different concentrations (10 micrograms/300 microliters and 100 micrograms/300 microliters) which were impregnated in 0.5 ml gelatin hydrogels was applied around the sutured allografts. Autografting was also done in 4 beagle dogs, with no bFGF application. One month after the grafting, no regenerating nerves extended beyond the middle of the transplant in any of the allografts, except in the autografts in which a number of regenerated (myelinated) axons were present. Three months after the grafting, an abundance of myelinated axons was found at the middle of the graft: the numbers of axons per 10(4) micron 2 were 22.6 in the autografts and 10.6, 10.4 and 19.2 in the allografts treated with no bFGF, low-dose bFGF, and high-dose bFGF, respectively. Regenerating axons extended into the host nerve: the numbers of myelinated axons at the level 1.5 cm distal to the distal suture were 35.7, 0.9, 3.8, and 12.1 per 10(4) micron 2 in the above respective order. Although it was inferior in quality to the autograft, peripheral nerve regeneration was extensive in the distal nerve using freeze-thawed and bFGF-treated allografts at 3 months. Electromyography showed that the peroneus longus muscle responded to the electrical stimuli given at the site proximal to the transplant in all four groups. These data indicate that a 5-cm acellular nerve segment containing Schwann cell basal laminae can be used successfully as an allograft without any immunosuppressants and that exogenously applied bFGF can improve nerve regeneration by enhancing the growth of regenerating axons.

After immunosuppressive therapy with Cyclosporin A (Cy-A) is stopped, nerve allograft rejection occurs. In addition to the loss of allogeneic perineurial, vascular, and Schwann cells, host axons that regenerate into the allograft disappear despite the fact that the axons are not foreign tissue. The present experiment was performed to correlate immune events and allogeneic cell and host axonal loss in nerve allografts after terminating Cy-A treatment. Nerve grafts (4 cm long) were taken from American Cancer Institute (ACI) rats and joined to the peroneal nerves of Fischer (FR) or ACI rats that received a daily dose of Cy-A (10 mg/kg, intraperitoneally). After one week, Cy-A therapy was stopped and the grafts were examined 2-6 weeks postoperatively by light and electron microscopy. No immune reaction nor destruction of perineural, vascular, or Schwann cells was found in 2- or 3-week-old allografts (i.e., ACI to FR grafts). These grafts underwent Wallerian degeneration and were invaded proximally by regenerating host axons, some of which were thinly myelinated. At 4 weeks, the perineurium of each allograft became infiltrated by mononuclear cells and was destroyed. Many of the endoneurial blood vessels of these grafts were occluded and their endothelial cells were degenerating or missing. Despite the immune reaction, allogeneic Schwann cells remained and continued to myelinate or ensheath host axons that had now grown up to 3 cm into the grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Explants from embryonic rat retina plated on Schwann cell monolayers were used to examine the mechanisms by which these central neurons interact with Schwann cell surfaces. Embryonic retinal explants extend neurites reliably on Schwann cell surfaces (Kleitman et al., 1988, J. Neurosci. 8: 653). Antibodies to molecules thought to be present on Schwann cell surfaces (laminin and the 217C antigen), on retinal neurite surfaces (Thy-1.1), or on both surfaces (L1) were tested for their ability to influence this neurite growth. Of these, only antibodies to L1 were effective in blocking retinal neurite extension on Schwann cells. Inhibition of neurite growth by anti-L1 was shown to be specific to growth on Schwann cell surfaces because neurite growth on air-dried collagen (a substratum known to support retinal neurite outgrowth) was not affected. This blockage was dose-dependent. At a low titer of anti-L1 Fab fragments defasciculation of neurites was prominent; at high titers 95% of neurite outgrowth was inhibited. This virtual elimination of the ability of Schwann cell surfaces to support embryonic retinal neurite growth in the presence of antibodies to L1 indicates that binding of the L1 molecule is a critical component of the mechanism by which Schwann cells foster the growth of these neurites. The present experiments concur with the growing body of evidence that L1 plays an important role in supporting neurite growth on cell surfaces and raise the possibility that L1 may also mediate the striking ability of adult retinal axons to regenerate in a peripheral nerve environment.

Peripheral nerve biopsies from patients with leprosy were stained with anti-Mycobacterium bovis (BCG) in a peroxidase-antiperoxidase (PAP) system to demonstrate intraneural mycobacterial antigens. Most M. leprae antigens have been shown to cross-react with BCG. Of the 30 biopsies from borderline tuberculoid (BT) patients 18 had acid-fast bacilli while 26 of them had demonstrable mycobacterial antigens in their nerves. All borderline lepromatous (BL) and lepromatous leprosy (LL) nerve biopsies had both M. leprae and mycobacterial antigens within them. Most of the antigens in the BT patients were seen to be extracellular. In BL and LL patients antigens were seen both extracellularly and intracellularly in Schwann cells and infiltrating macrophages. Mycobacterial antigens in BT nerves were always seen to be surrounded by a mononuclear cell reaction while in the BL and LL patients antigens could be seen with minimal cellular infiltrate and the neural architecture was more or less preserved. While bacilli could not be seen in BT patients who had been released from treatment for more than 4 years, mycobacterial antigens could still be seen in some patients who had been released from treatment for up to 5 years. Patients with no skin lesions but with large, painful, or tender nerves were found to have intraneural inflammation surrounding mycobacterial antigens, while those with a similar clinical picture but without tender or painful nerves showed no marked inflammation within their nerves despite the presence of mycobacterial antigens. From these findings it was concluded that immunologically mediated inflammatory response toward intraneurally located M. leprae antigens in conjunction with other host factors may be necessary for nerve damage in the BT leprosy patients. In the BL and LL patients the mechanisms of nerve damage are still unknown with certainty but local effects and immune-complex damage secondary to abundant M. leprae antigens are worth exploring. The use of immunohistological techniques should offer a new approach in the study of the immunopathology of leprosy.