Peripheral nerve injury causes transient expression of MHC class I antigens in rat motor neurons and skeletal muscles

Neuronal Presentation of Antigen and Its Possible Role in Parkinson's Disease

Patients with Parkinson's disease (PD) and other synucleinopathies often exhibit autoimmune features, including CD4+ and some CD8+ T lymphocytes that recognize epitopes derived from alpha-synuclein. While neurons have long been considered to not present antigens, recent data indicate that they can be induced to do so, particularly in response to interferons and other forms of stress. Here, we review literature on neuronal antigen presentation and its potential role in PD. Although direct evidence for CD8+ T cell-mediated neuronal death is lacking in PD, neuronal antigen presentation appears central to the pathology of Rasmussen's encephalitis, a pediatric neurological disorder driven by cytotoxic T cell infiltration and neuroinflammation. Emerging data suggest that T cells enter the brain in PD and other synucleinopathies, where the majority of neuromelanin-containing substantia nigra and locus coeruleus neurons express MHC Class I molecules. In cell culture, CD8+ T cell recognition of antigen:MHC Class I complexes on neuronal membranes leads to cytotoxic responses and neuronal cell death. Recent animal models suggest the possibility of T cell autoreactivity to mitochondrial antigens in PD. It remains unclear if neuronal antigen presentation plays a role in PD or other neurodegenerative disorders, and efforts are underway to better elucidate the potential impact of autoimmune responses on neurodegeneration.

Synaptic Plasticity on Motoneurons After Axotomy: A Necessary Change in Paradigm

Motoneurons axotomized by peripheral nerve injuries experience profound changes in their synaptic inputs that are associated with a neuroinflammatory response that includes local microglia and astrocytes. This reaction is conserved across different types of motoneurons, injuries, and species, but also displays many unique features in each particular case. These reactions have been amply studied, but there is still a lack of knowledge on their functional significance and mechanisms. In this review article, we compiled data from many different fields to generate a comprehensive conceptual framework to best interpret past data and spawn new hypotheses and research. We propose that synaptic plasticity around axotomized motoneurons should be divided into two distinct processes. First, a rapid cell-autonomous, microglia-independent shedding of synapses from motoneuron cell bodies and proximal dendrites that is reversible after muscle reinnervation. Second, a slower mechanism that is microglia-dependent and permanently alters spinal cord circuitry by fully eliminating from the ventral horn the axon collaterals of peripherally injured and regenerating sensory Ia afferent proprioceptors. This removes this input from cell bodies and throughout the dendritic tree of axotomized motoneurons as well as from many other spinal neurons, thus reconfiguring ventral horn motor circuitries to function after regeneration without direct sensory feedback from muscle. This process is modulated by injury severity, suggesting a correlation with poor regeneration specificity due to sensory and motor axons targeting errors in the periphery that likely render Ia afferent connectivity in the ventral horn nonadaptive. In contrast, reversible synaptic changes on the cell bodies occur only while motoneurons are regenerating. This cell-autonomous process displays unique features according to motoneuron type and modulation by local microglia and astrocytes and generally results in a transient reduction of fast synaptic activity that is probably replaced by embryonic-like slow GABA depolarizations, proposed to relate to regenerative mechanisms.

Temporospatial Analysis and New Players in the Immunology of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by progressive loss of lower and upper motor neurons (MN) leading to muscle weakness, paralysis and eventually death. Although a highly varied etiology results in ALS, it broadly manifests itself as sporadic and familial forms that have evident similarities in clinical symptoms and disease progression. There is a tremendous amount of knowledge on molecular mechanisms leading to loss of MNs and neuromuscular junctions (NMJ) as major determinants of disease onset, severity and progression in ALS. Specifically, two main opposing hypotheses, the dying forward and dying back phenomena, exist to account for NMJ denervation. The former hypothesis proposes that the earliest degeneration occurs at the central MNs and proceeds to the NMJ, whereas in the latter, the peripheral NMJ is the site of precipitating degeneration progressing backwards to the MN cell body. A large body of literature strongly indicates a role for the immune system in disease onset and progression via regulatory involvement at the level of both the central and peripheral nervous systems (CNS and PNS). In this review, we discuss the earliest reported immune responses with an emphasis on newly identified immune players in mutant superoxide dismutase 1 (mSOD1) transgenic mice, the gold standard mouse model for ALS.

Loss of class I MHC function alters behavior and stress reactivity

The importance of the classical immune molecule, class I major histocompatibility complex to central nervous system function is one of the most surprising discoveries related to neuroimmunology in the past decade. Mice lacking both β-2microglobulin and transporter associated with antigen processing (β2M-/-TAP-/-) showed differences in basal behavior. In response to saline injection, β2M-/-TAP-/- mice showed a significant hypothalamic pituitary adrenal activation that was not observed in wild type mice, while lipopolysaccharide-induced cytokine expression in the hypothalamus was similar in β2M-/-TAP-/- and wild type mice. Overall, these data show that class I MHC plays an important role in behavior and stress reactivity.

Novel roles for immune molecules in neural development: implications for neurodevelopmental disorders

Although the brain has classically been considered “immune-privileged”, current research suggests an extensive communication between the immune and nervous systems in both health and disease. Recent studies demonstrate that immune molecules are present at the right place and time to modulate the development and function of the healthy and diseased central nervous system (CNS). Indeed, immune molecules play integral roles in the CNS throughout neural development, including affecting neurogenesis, neuronal migration, axon guidance, synapse formation, activity-dependent refinement of circuits, and synaptic plasticity. Moreover, the roles of individual immune molecules in the nervous system may change over development. This review focuses on the effects of immune molecules on neuronal connections in the mammalian central nervous system – specifically the roles for MHCI and its receptors, complement, and cytokines on the function, refinement, and plasticity of geniculate, cortical and hippocampal synapses, and their relationship to neurodevelopmental disorders. These functions for immune molecules during neural development suggest that they could also mediate pathological responses to chronic elevations of cytokines in neurodevelopmental disorders, including autism spectrum disorders (ASD) and schizophrenia.

Classical major histocompatibility complex class I molecules in motoneurons: new actors at the neuromuscular junction

Major histocompatibility complex (MHC) class I molecules have fundamental functions in the immune system. Recent studies have suggested that these molecules may also have non-immune functions in the nervous system, in particular related to synaptic function and plasticity. Because adult motoneurons express mRNAs for MHC class I molecules, we have examined their subcellular expression pattern in vivo and their role for the synaptic connectivity of these neurons. We observed immunoreactivity for classical MHC class I (Ia) protein in motoneuron somata, but the predominant expression was found in axons and presynaptically at neuromuscular junctions (NMJs). Peripheral nerve lesion induced a strong increase of motoneuron MHC class Ia (H2-K(b)/D(b)) mRNA, indicating a role for MHC class Ia molecules during regeneration. Accordingly, there was an accumulation of MHC class Ia proteins at the cut ends and in growth cones of motor axons after lesion. In K(b-/-)D(b-/-) mice (lacking MHC class Ia molecules), the time course for recovery of grip ability in reinnervated muscles was significantly delayed. Muscles from K(b-/-)D(b-/-) mice displayed an increased density and a disturbed distribution of NMJs and fewer terminal Schwann cells/NMJ compared with wild-type mice. A population of Schwann cells in sciatic nerves expressed the paired Ig receptor B, which binds to MHC class I molecules. These results provide the first evidence that neuronal MHC class Ia molecules are present in motor axons, that they are important for organization of NMJs and motor recovery after nerve lesion, and that their actions may be mediated via Schwann cells.

Immune proteins in brain development and synaptic plasticity

Many proteins first identified in the immune system are also expressed in the developing and adult nervous system. Unexpectedly, recent studies reveal that a number of these proteins, in addition to their immunological roles, are essential for the establishment, function, and modification of synaptic connections. These include proinflammatory cytokines (e.g., TNFalpha, IL-6), proteins of the innate immune system (e.g., complement C1q and C3, pentraxins, Dscam), members of the major histocompatibility complex class I (MHCI) family, and MHCI-binding immunoreceptors and their components (e.g., PIRB, Ly49, DAP12, CD3zeta). Understanding how these proteins function in neurons will clarify the molecular basis of fundamental events in brain development and plasticity and may add a new dimension to our understanding of neural-immune interactions in health and disease.

The microglial networks of the brain and their role in neuronal network plasticity after lesion

Microglia are the resident inflammatory cells of the central nervous system (CNS) extending a network of processes in the CNS parenchyma. Following axon lesion to neurons, most extensively studied in motoneurons, there is a typical retrograde response at the cell body level, including the removal or 'stripping' of synapses from the perikaryon and dendrites of affected cells. Microglia have been attributed a main and active role in this process, although also an involvement of activated astrocytes has been suggested. The signaling pathways for this 'synaptic stripping' have so far been unknown, but recently some classical immune recognition molecules, the MHC class I molecules, have been shown to have a strong influence on the strength and pattern of the synapse elimination response. Since there is an expression of MHC class I in both neurons and glia, in particular microglia, as well as MHC class I related receptors in axons and microglia, there are good reasons to believe that classical immune recognition signaling between neurons and glia underlies part of the 'stripping' response. A role for microglia in an interplay with synapses based on this type of signaling is further exemplified by the fact that, in the absence of some MHC class I related receptors normally found on microglia during development, profound effects on synaptic function and biochemistry have been demonstrated. Such effects may be linked to the development of various disorders of the CNS, such as degenerative disease.

Immune cell involvement in dorsal root ganglia and spinal cord after chronic constriction or transection of the rat sciatic nerve

Chronic constriction injury (CCI) of the sciatic nerve in rodents produces mechanical and thermal hyperalgesia and is a common model of neuropathic pain. Here we compare the inflammatory responses in L4/5 dorsal root ganglia (DRGs) and spinal segments after CCI with those after transection and ligation at the same site. Expression of ATF3 after one week implied that 75% of sensory and 100% of motor neurones had been axotomized after CCI. Macrophage invasion of DRGs and microglial and astrocytic activation in the spinal cord were qualitatively similar but quantitatively distinct between the lesions. The macrophage and glial reactions around neurone somata in DRGs and ventral horn were slightly greater after transection than CCI while, in the dorsal horn, microglial activation (using markers OX-42(for CD11b) and ED1(for CD68)) was greater after CCI. In DRGs, macrophages positive for OX-42(CD11b), CD4, MHC II and ED1(CD68) more frequently formed perineuronal rings beneath the glial sheath of ATF3+ medium to large neurone somata after CCI. There were more invading MHC II+ macrophages lacking OX-42(CD11b)/CD4/ED1(CD68) after transection. MHC I was expressed in DRGs and in spinal sciatic territories to a similar extent after both lesions. CD8+ T-lymphocytes aggregated to a greater extent both in DRGs and the dorsal horn after CCI, but in the ventral horn after transection. This occurred mainly by migration, additional T-cells being recruited only after CCI. Some of these were probably CD4+. It appears that inflammation of the peripheral nerve trunk after CCI triggers an adaptive immune response not seen after axotomy.

Effects of oestrogen on trigeminal ganglia in culture: implications for hormonal effects on migraine

Although migraine is more common in women than men and often linked to the menstrual cycle, few studies have investigated the biological basis of hormonal influences on the trigeminovascular system. In the present study we investigated the effect of physiological levels (10(-9) m) oestrogen on female rat trigeminal ganglia in vitro. Immunocytochemical analysis demonstrated the presence of oestrogen receptor-alpha in a predominantly cytoplasmic location and in neurites. Microarray analysis demonstrated that oestrogen treatment regulates several genes with potential relevance to menstrual migraine. The genes that were upregulated included synapsin-2, endothelin receptor type B, activity and neurotransmitter-induced early gene 7 (ania-7), phosphoserine aminotransferase, MHC-1b, and ERK-1. Down-regulated genes included IL-R1, bradykinin B2 receptor, N-tropomodulin, CCL20, GABA transporter protein, fetal intestinal lactase-phlorizin hydrolase, carcinoembryonic antigen-related protein, zinc finger protein 36, epsin 1 and cysteine string protein. Protein activity assays demonstrated that exposure of the cultured neurons to oestrogen leads to activation of ERK, which has been linked to inflammatory pain. Immunocytochemistry demonstrated that activated ERK was present in neurons containing peripherin, a marker of nociceptive neurons. Several of the genes in the present study may provide potential targets for understanding the association of oestrogen with migraine and other hormone-related orofacial pain.

Expression of a killer cell receptor-like gene in plastic regions of the central nervous system

A property common to the immune system and the nervous system is regulation by a highly complex and adaptable network of cellular interactions. Major histocompatibility complex (MHC) class I molecules, which are ligands of antigen-specific receptors on CD8 T cells and of inhibitory receptors on natural killer cells, have an important and surprising role in the control of activity-dependent neuronal plasticity in the central nervous system (CNS). While expression of MHC class I molecules in neurons has been reported, corresponding immune receptors have not been identified in the CNS. Here we show selective expression of a gene related to killer cell immunoglobulin-like receptor (KIR) genes in subregions of the mouse brain where synaptic plasticity and neurogenesis occur, including olfactory bulbs, rostral migratory stream and dentate gyrus of hippocampus. These results suggest new functions for KIR-like molecules in the CNS.

A role for MHC class I molecules in synaptic plasticity and regeneration of neurons after axotomy

Recently, MHC class I molecules have been shown to be important for the retraction of synaptic connections that normally occurs during development [Huh, G.S., Boulanger, L. M., Du, H., Riquelme, P. A., Brotz, T. M. & Shatz, C. J. (2000) Science 290, 2155-2158]. In the adult CNS, a classical response of neurons to axon lesion is the detachment of synapses from the cell body and dendrites. We have investigated whether MHC I molecules are involved also in this type of synaptic detachment by studying the synaptic input to sciatic motoneurons at 1 week after peripheral nerve transection in beta2-microglobulin or transporter associated with antigen processing 1-null mutant mice, in which cell surface MHC I expression is impaired. Surprisingly, lesioned motoneurons in mutant mice showed more extensive synaptic detachments than those in wild-type animals. This surplus removal of synapses was entirely directed toward inhibitory synapses assembled in clusters. In parallel, a significantly smaller population of motoneurons reinnervated the distal stump of the transected sciatic nerve in mutants. MHC I molecules, which traditionally have been linked with immunological mechanisms, are thus crucial for a selective maintenance of synapses during the synaptic removal process in neurons after lesion, and the lack of MHC I expression may impede the ability of neurons to regenerate axons.

Effects of interferon-gamma on neuronal infections

IFN-gamma is released in the brain, not only during acute infectious diseases or immunological reactions, but also for extended periods of time after clearance of infectious virus and during viral latency. In this review, we focus on the role of IFN-gamma in the interaction between a neuron and a pathogen, that is, the role in implementation of microbial destruction, stasis or persistence, its potential neuroprotective or toxic effects, and how this cytokine may affect neuronal function and the behavior of an individual.

Induced neuronal expression of class I major histocompatibility complex mRNA in acute and chronic inflammation models

Studies have demonstrated neuronal expression of class I major histocompatibility complex (MHC) mRNA and protein in normal and developing brain and in response to injury or viral infection. We report neuronal expression of class I MHC mRNA in hypothalamic paraventricular nucleus (PVN) neurons in rats following systemic infection with Trypanosoma brucei brucei parasites (chronic) and in response to intravenous 1 mg/kg lipopolysaccharide administration (acute peripheral) and in striatal neurons following intrastriatal 5 microg lipopolysaccharide injection (acute central). These results demonstrate that neurons can be a source of immune signaling molecules and establish class I MHC as part of the neuronal component of immune responses.

Re-expression of Nerve Growth Factor Receptor after Axonal Injury Recapitulates a Developmental Event in Motor Neurons: Differential Regulation when Regeneration is Allowed or Prevented

Motor neurons in the brainstem and spinal cord transiently express nerve growth factor receptors (NGFr) during development, but not in normal adult animals. In this study, NGFr was immunohistochemically identified in hypoglossal motor neurons after different types of peripheral axonal injury in adult rats. NGFr is re-expressed in motor neurons 7 days after a nerve crush injury, and has disappeared again by 28 days. These times correspond, respectively, to the active phase of regeneration, and a time by which regeneration has largely been completed, as determined by electrical activation of tongue muscle twitch. In contrast, 7 days after nerve transection and ligation of the proximal stump to prevent regeneration, there is no re-expression of NGFr, but 28 days after such treatment NGFr is present in a few neurons. By this time, neuroma formation has begun proximal to the end of the cut and ligated nerve. Together, these findings suggest that motor neurons transiently re-express NGFr during regeneration and not in response to axonal transection per se. The signal triggering re-expression thus seems more likely to be the introduction of a message from the site of injury, rather than the loss of a target-derived message. Although the function of NGFr in developing and regenerating motor neurons is not known, its expression appears to be associated with periods of axonal growth and maturation.

Immune-mediated protection from measles virus-induced central nervous system disease is noncytolytic and gamma interferon dependent

Neurons of the mammalian central nervous system (CNS) are an essential and largely nonrenewable cell population. Thus, virus infections that result in neuronal depletion, either by virus-mediated cell death or by induction of the cytolytic immune response, could cause permanent neurological impairment of the host. In a transgenic mouse model of measles virus (MV) infection of neurons, we have previously shown that the host T-cell response was required for resolution of infection in susceptible adult mice. In this report, we show that this protective response did not result in neuronal death, even during the peak of T-cell infiltration into the brain parenchyma. When susceptible mice were intercrossed with specific immune knockout mice, a critical role for gamma interferon (IFN-gamma) was identified in protection against MV infection and CNS disease. Moreover, the addition of previously activated splenocytes or recombinant murine IFN-gamma to MV-infected primary neurons resulted in the inhibition of viral replication in the absence of neuronal death. Together, these data support the hypothesis that the host immune response can promote viral clearance without concomitant neuronal loss, a process that appears to be mediated by cytokines.

Expression of MHC class I heavy chain and beta2-microglobulin in rat brainstem motoneurons and nigral dopaminergic neurons

We demonstrate here that motoneurons and nigral dopaminergic neurons in the brainstem of the adult rat, with the exception of motoneurons innervating ocular muscles, display high levels of both MHC class I heavy chain and beta2-microglobulin mRNAs. These neurons also display interferon-gamma receptor mRNA. We find it striking that these particular neurons are those which are vulnerable to neurodegeneration in diseases such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS).

Cell surface expression of H2 antigens on primary sensory neurons in response to acute but not latent herpes simplex virus infection in vivo

CD8(+) T lymphocytes and class I major histocompatibility complex (MHC-I) molecules profoundly influence the severity of neuronal herpes simplex virus (HSV) infection in experimentally infected mice. Paradoxically, neurons are classically regarded as MHC-I deficient. However, it is shown here that H2-encoded heavy chains (alphaCs) and their associated light chain, beta2 microglobulin, are present on the surfaces of primary sensory neurons recovered from sensory ganglia within 1 to 2 weeks of HSV infection. During this time, some neurons are found to be tightly associated with T cells in vivo. Prior data showed that termination of productive HSV infection in the peripheral nervous system is not dependent on cell-mediated lysis of infected neurons. Consistent with these data, immunogold electron microscopy showed that the density of cell surface H2 on neurons is an order of magnitude lower than on satellite glia, which is predicted to favor a noncytolytic CD8 cell response.

Expression of MHC class I and beta2-microglobulin in rat spinal motoneurons: regulatory influences by IFN-gamma and axotomy

The low expression of MHC antigens is believed to be one factor of importance contributing to the immune-privileged status of CNS neurons. We here describe that motoneurons, in contrast to other nerve cells in the lumbar spinal cord of the adult rat, express both MHC class I and beta2-microglobulin mRNA. The motoneurons also display in situ hybridization signal for IFN-gamma receptor mRNA. After a peripheral axotomy, the motoneurons show a clear upregulation of beta2-microglobulin mRNA. IFN-gamma treatment of cultured rat embryonic spinal motoneurons causes a similar upregulation of especially beta2-microglobulin. Based on these facts, we propose that spinal motoneurons can be influenced by IFN-gamma and recognized by cytotoxic CD8+ T-cells. These findings could be of relevance in the search for pathogenetic mechanisms in motoneuron-specific diseases, such as ALS.

Human leukocyte antigen class I in polymyositis: leukocyte infiltrates, regeneration, and impulse block

In polymyositis (PM), T-cell mediated myocytotoxicity is directed against strongly human leukocyte antigen class I positive (HLA-I+) muscle fibers. Fiber regeneration probably is partly responsible for this HLA-I up-regulation. We have evaluated regeneration, denervation/impulse blockade, and focal leukocyte infiltrates as possible HLA-I inducing factors in PM. Distinctive patterns of HLA-I, nerve cell adhesion molecule (NCAM), and vimentin expression accompany denervation and regeneration. Regenerating fibers also have centralized nuclei. Using semiquantitative methods, we examined strongly HLA-I+ fibers in PM muscle biopsies for these markers. Sarcoplasmic HLA-I levels were related to the presence of leukocyte infiltrates and invasion of fibers. Strongly HLA-I+ fibers were frequently invaded, and regeneration-associated changes were usually observed at sites of fiber damage. Sarcoplasmic HLA-I levels were stable along intact fibers, also adjacent to leukocyte infiltrates. A majority of the strongly HLA-I+ fibers were nonregenerating (NCAM+ only). Though other mechanisms cannot be excluded, this suggests that impulse blockade or denervation may contribute to extra HLA-I up-regulation in these fibers.

Up-regulation of leukaemia inhibitory factor and interleukin-6 in transected sciatic nerve and muscle following denervation

Leukaemia inhibitory factor (LIF) and Interleukin-6 (IL-6) are multifunctional cytokines that are related on the basis of their predicted structural similarities and shared signal transducing receptor components. Both these factors stimulate myoblast proliferation, and whereas LIF is neurotrophic for sensory neurons, and for the motor neurons which innervate muscle, IL-6 has only been reported to act on a population of septal neurons in the brain. We have looked at the effect of peripheral nerve trauma on the expression of these factors. We show here that whereas LIF and IL-6 mRNAs are expressed in low levels in normal sciatic nerve and skeletal muscle, there is significant up-regulation in the nerve segments after injury, with proximally and distally. There is also an increase in LIF and IL-6 expression in the denervated muscle located largely in the muscle cells. In addition, while there is retrograde axonal transport of LIF by the sciatic nerve, IL-6 is not retrogradely transported, and as a result, IL-6 does not stimulate the survival of sensory neurons in vitro. Both growth factors are produced by Schwann cells. These results show a rapid response in the expression of these genes after injury and suggest that LIF and IL-6 act as trauma factors but with different roles in injured peripheral nerve.

Immunization with plasmid DNA using a pneumatic gun

We characterize a method by which the Med-E-Jet pneumatic vaccination gun can be used to propel intact, supercoiled plasmid DNA through skin and into skeletal muscles of mice. Intramuscular injection of plasmids containing the firefly luciferase gene linked to the human cytomegalovirus promoter resulted in the expression of several hundred picograms of luciferase enzyme in quadriceps muscles. Intramuscular injections of a plasmid containing the influenza A nuclear protein gene regulated by the same promoter resulted in the generation of potent and specific anti-nuclear protein humoral and cellular immune responses. This convenient and rapid injection method would be well-suited for genetic immunization of humans.

Cytokine induction during T-cell-mediated clearance of mouse hepatitis virus from neurons in vivo

To investigate the mechanism by which viruses are cleared from neurons in the central nervous system, we have utilized a mouse model involving infection with a neurotropic variant of mouse hepatitis virus (OBLV60). After intranasal inoculation, OBLV60 grew preferentially in the olfactory bulbs of BALB/c mice. Using in situ hybridization, we found that viral RNA localized primarily in the outer layers of the olfactory bulb, including neurons of the mitral cell layer. Virus was cleared rapidly from the olfactory bulb between 5 and 11 days. Athymic nude mice failed to eliminate the virus, demonstrating a requirement for T lymphocytes. Immunosuppression of normal mice with cyclophosphamide also prevented clearance. Both CD4+ and CD8+ T-cell subsets were important, as depletion of either of these subsets delayed viral clearance. Gliosis and infiltrates of CD4+ and CD8+ cells were detected by immunohistochemical analysis at 6 days. The role of cytokines in clearance was investigated by using an RNase protection assay for interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-2, IL-3, IL-4, IL-5, IL-6, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and gamma interferon (IFN-gamma). In immunocompetent mice there was upregulation of RNA for IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, and IFN-gamma at the time of clearance. Nude mice had comparable increases in these cytokine messages, with the exception of IFN-gamma. Induction of major histocompatibility complex class I (MHC-I) molecules on cells in infected brains was demonstrated by immunohistochemical analyses in normal and nude mice, suggesting that IFN-gamma may not be necessary for induction of MHC-I on neural cells in vivo.

Co-induction of neuronal interferon-gamma and nitric oxide synthase in rat motor neurons after axotomy: a role in nerve repair or death?

Induction of an interferon-gamma-like molecule, previously isolated from neurons (N-IFN-gamma), and of the neuronal isoform I of the synthetic enzyme of the free radical nitric oxide, nitric oxide synthase I, as well as of NADPH-diaphorase, were examined in axotomized dorsal motor vagal and hypoglossal neurons. Unilateral transection of the vagal and hypoglossal nerves was performed in the same rat and an induction of N-IFN-gamma and nitric oxide synthase I immunostaining as well as NADPH-diaphorase histochemical positivity was observed in the ipsilateral motoneurons after 2-4 days. The immuno- and enzyme-histochemical positivities were much stronger in the dorsal motor vagal neurons than in hypoglossal neurons. Two and 4 weeks after axotomy N-IFN-gamma immunoreactivity and NADPH-diaphorase positivity persisted in the former, but started to decrease in the latter neurons. Previous data have shown that 23 weeks after nerve transection the majority of the dorsal motor vagal neurons are lost, while the majority of the hypoglossal neurons survive. The high and persistent expression of N-IFN-gamma and nitric oxide synthase I after axotomy in the dorsal motor vagal neurons, that are largely destined to die, indicates that the co-induction of these two molecules may be implicated in the pathogenesis of neuronal degeneration.

Nerve-evoked electrical activity regulates molecules and cells with immunological function in rat muscle tissue

Molecules coded by the major histocompatibility complex (MHC) are present on cell surfaces in most tissues, with the cells of the central nervous system and skeletal muscle as prominent exceptions. We show here that when rat skeletal muscles are rendered inactive by nerve impulse block, expression of MHC class I molecules occurs on the muscle fibres. In addition, the number of cells expressing MHC class II molecules in the muscle interstitium is increased by a factor of three after 2 weeks of impulse blockade. Similar effects obtained by denervation can be counteracted by direct electrical stimulation. Interferon-gamma-like immunoreactivity accumulates in inactive muscle fibres, and interferon-gamma or a related cytokine could be a link between inactivity and MHC up-regulation. These findings suggest that nerve-evoked muscle activity influences not only the phenotype of the muscle cells themselves, but also processes in the interstitium that may increase the immunoreactivity of inactive muscle tissue.

Neuronal interferon-gamma immunoreactive molecule: bioactivities and purification

An interferon (IFN)-gamma immunoreactive molecule, localized to small neurons in peripheral sensory ganglia (N-IFN-gamma), has been detected with two mouse monoclonal antibodies (DB1 and DB16) directed against different epitopes of rat IFN-gamma. To define N-IFN-gamma with regard to its protein characteristics and bioactivities, DB1 and DB16 were used to purify N-IFN-gamma from rat trigeminal ganglia in a two-step sequential antibody-affinity procedure. Sodium dodecylsulfate polyacrylamide gel electrophoresis (PAGE) and silver staining of purified N-IFN-gamma displayed three bands with an approximate molecular mass of 66, 62 and 54 kDa. The N-IFN-gamma bioactivity was confined to the protein stained on gel when native material was run on PAGE. Biological effects of pure N-IFN-gamma were examined and compared with those of lymphocyte-derived recombinant IFN-gamma. N-IFN-gamma had antiviral effects in vitro and induced major histocompatibility complex class I and II antigens on macrophages and in cells in skeletal muscle cell cultures. N-IFN-gamma also stimulated myoblast proliferation and affected cholinergic receptor distribution on myotubes similar to recombinant IFN-gamma. Both molecules potently stimulated Trypanosoma brucei brucei growth. These data suggest that, although N-IFN-gamma is a protein distinct from lymphocyte-derived IFN-gamma, the two molecules have enough structural similarities to allow for antibody recognition of at least two epitopes, and action on similar target structures on both parasite and mammalian cells.

Induction of class I major histocompatibility complex antigens on adult primate retinal neurons

The expression of class I major histocompatibility complex (MHC) antigens was examined on adult monkey and human retinal cells following injury caused by dissociation. In a panning assay, neurons and glia demonstrated a rapid induction of class I MHC antigens following enzymatic dissociation, and expression was sustained on regenerating neurons as well as on glia in culture. Class I MHC antigen expression was also enhanced following optic nerve crush of monkey eyes in vivo. These results suggest that the functions of class I MHC antigens may be relevant to primate CNS neurons and glia following injury.

Class II MHC antigens in normal human skeletal muscle

Class II MHC antigen expression has been investigated in muscle tissue and cultured cells from normal human skeletal muscle by light and electron immunocytochemistry. In muscle tissue, these antigens were detected in satellite cells, interstitial cells, and blood vessels. In cultures, muscle cells were stained with a pan-reactive anti-HLA class II antibody and with isotypes specific for DP, DQ, and DR. The staining was present on mononucleated cells and persisted on myotubes; it was stronger for DR and DQ isotypes than for DP. At the subcellular level, staining was located not only at the cell surface, but also next to the endoplasmic reticulum and in the cytosol. Thus, myosatellite cells and aneurally cultured cells from human normal skeletal muscle express class II MHC antigens. Moreover, the myotube staining and the presence of gold particles inside the cells suggested synthesis of these antigens after myoblast fusion.

Comparison of stimulation and insulin effects on denervated mouse soleus muscles

A comparison has been made between the responses of denervated mouse soleus muscles to direct electrical stimulation, as reported by earlier workers, and to incubation with supraphysiological concentrations of insulin. The parameters of interest were resting membrane potential (RMP), qualities of the active state, the amount of alpha bungarotoxin (BUTX) binding, and chemosensitivity, as measured by the strength of acetylcholine (ACh)-induced contractures. In all aspects, the changes recorded after insulin, were in the same direction as with direct stimulation, however, owing to the time limitations of in vitro testing, were smaller. It is suggested that the effects of electric shocks on denervated muscles are the result of activation of the insulin receptor, or some similar macromolecule, which appears to be sensitive to the membrane potential. The possible interrelations between acetylcholine and insulin receptors in neurotrophic control are discussed.

Interferon-gamma-like immunoreactivity in developing rat spinal ganglia neurons in vivo and in vitro

Interferon-gamma-like immunoreactivity was observed in a subpopulation of 16-day-old embryonic rat spinal ganglion neurons using two monoclonal antibodies directed against different epitopes of recombinant interferon-gamma. During ontogenesis both in vivo and in vitro, it was found that the strong immunoreactivity was confined to small neurons when neurons become morphologically distinct on the basis of size. In vivo, the interferon-gamma-immunoreactive neurons started to express major histocompatibility complex class I antigens after the first postnatal week, while in vitro no such antigen could be detected. A quantitative Elisa method was developed to determine the levels of major histocompatibility complex class I and interferon-gamma in vitro, whereby increased amounts of major histocompatibility complex class I antigen was detected after exposing the cultures to recombinant interferon-gamma and Sendai virus. Sendai virus also caused a small increase in interferon-gamma with a peak about 12 hours after infection. The in vitro system will be used to study further the role of the putative neuronal interferon-gamma-like molecule in the regulation of cell growth, for induction of major histocompatibility complex antigens and in virus infection of sensory neurons.

Mechanisms of allograft rejection in the rat brain

Embryonic rat hippocampal primordia from class I and class II major histoincompatible donors were transplanted into the hippocampus of adult rat hosts. The allografts were rejected by a specific host immune response, which was identified by reference to events at a histocompatible hippocampal primordial graft (syngeneic to the host) of similar embryonic age placed simultaneously in the contralateral hippocampus of the same hosts. The present combined light immunohistochemical and electron microscopic study was undertaken to elucidate the mechanism of induction of the immune response by a graft of a tissue which does not constitutively express major histocompatibility antigens, to identify which cells are involved, and how they enter the brain and attack the graft, and to look for possible sources of variability in the outcome of such an attack. Our main findings are (1) that host and graft microglia play a prominent role from the earliest stages, and throughout the evolution of the histological changes, (2) that the later entry of host dendritic cells, lymphocytes, and lymphoblasts (with associated mitoses) into the perivascular cuffs of the graft vasculature ensures that the local immune response becomes self-propagating, (3) that the allografted neurons are killed by host cytotoxic lymphocytes only after a previous encirclement by host macrophage-derived microglial cells, and (4) that the observed variability (especially within different regions of a single allograft) is associated not with failure of immune induction, but with local failure of the graft tissues to express allotypic major histocompatibility antigens. Our observations confirm that once the host immune system has been primed, local factors leading to the induction of transplant major histocompatibility complex antigens make histoincompatible intracerebral transplants of embryonic into adult brain tissue vulnerable to vigorous and effective immune attack. The histological picture of the immune response observed in our intracerebral allografts resembles that described in intraventricular allografts of embryonic brain, in allografts of other organs and tissues such as skin, kidney, and heart, and also that seen in the response to brain autoantigens in multiple sclerosis and experimental allergic encephalomyelitis. However, the involvement of a special cell type, the perivascular microglial cell, in the early stages of immune induction in brain raises the possibility of designing future therapeutic approaches which might selectively block this step in conditions such as multiple sclerosis.

Interferon-gamma-like immunoreactivity and T-cell marker expression in rat skeletal muscle fibres

Interferon-gamma (IFN-gamma)-like-immunoreactivity was observed in subsets of rat skeletal muscle fibres with 3 different mouse monoclonal antibodies directed to rat IFN-gamma and a rabbit polyclonal anti-rat IFN-gamma-antibody. These strongly IFN-gamma-immunoreactive fibres also expressed antigen defining T-cells of the cytotoxic/suppressor phenotype (CD8) and major histocompatibility complex (MHC) class I antigen.

Local enhancement of major histocompatibility complex (MHC) class I and II expression and cell infiltration in experimental allergic encephalomyelitis around axotomized motor neurons

The effect of unilateral peripheral nerve lesions on the inflammatory response of experimental allergic encephalomyelitis (EAE) in rat central nervous system (CNS) was studied. Immunostaining for major histocompatibility complex (MHC) antigens and T-cell subsets demonstrated that MHC class I expression was markedly enhanced in as well as around axotomized motor neurons and that MHC class II expression was induced on several cells, probably microglial cells, in close proximity to the axotomized motor neurons. There was also a pronounced increase in interleukin 2 receptor-positive lymphocytes as well as T-cells and the T-cell subsets on the injured as compared to the non-injured contralateral side. These effects were present particularly in the initial phase of EAE and persisted for several weeks. The results suggest that neurons may communicate immunoregulatory signals to their microenvironment and that retrograde axonal signals from the distant periphery may alter the immune response locally within the CNS.