M. leprae components induce nerve damage by complement activation: identification of lipoarabinomannan as the dominant complement activator.

Peripheral nerve damage is the hallmark of leprosy pathology but its etiology is unclear. We previously identified the membrane attack complex (MAC) of the complement system as a key determinant of post-traumatic nerve damage and demonstrated that its inhibition is neuroprotective. Here, we determined the contribution of the MAC to nerve damage caused by Mycobacterium leprae and its components in mouse. Furthermore, we studied the association between MAC and the key M. leprae component lipoarabinomannan (LAM) in nerve biopsies of leprosy patients. Intraneural injections of M. leprae sonicate induced MAC deposition and pathological changes in the mouse nerve, whereas MAC inhibition preserved myelin and axons. Complement activation occurred mainly via the lectin pathway and the principal activator was LAM. In leprosy nerves, the extent of LAM and MAC immunoreactivity was robust and significantly higher in multibacillary compared to paucibacillary donors (p = 0.01 and p = 0.001, respectively), with a highly significant association between LAM and MAC in the diseased samples (r = 0.9601, p = 0.0001). Further, MAC co-localized with LAM on axons, pointing to a role for this M. leprae antigen in complement activation and nerve damage in leprosy. Our findings demonstrate that MAC contributes to nerve damage in a model of M. leprae-induced nerve injury and its inhibition is neuroprotective. In addition, our data identified LAM as the key pathogen associated molecule that activates complement and causes nerve damage. Taken together our data imply an important role of complement in nerve damage in leprosy and may inform the development of novel therapeutics for patients.

The demyelination neurophysiological criteria can be misleading in Campylobacter jejuni-related Guillain-Barré syndrome.

OBJECTIVE: The exclusive association of Campylobacter jejuni infection with the axonal variant of Guillain-Barré syndrome (GBS) is debatable. The current study aims to elucidate the GBS subtypes of patients with an antecedent C. jejuni infection. METHODS: Nerve conduction study results of 73 patients with GBS were reviewed. Patients were defined as having a recent C. jejuni infection when there was a positive stool culture or serological evidence of C. jejuni in the presence of preceding diarrhea. RESULTS: A total of 23 patients had evidence of a recent C. jejuni infection. At the early stage, patients were classified as AMAN (n=9; 39%), AIDP (n=3; 13%) or equivocal (n=9) using existing electrophysiological criteria. Prolonged distal latencies and conduction slowing that were seen in 11 patients rapidly normalized within 3 weeks in seven, whereas four had minor abnormalities throughout the course. Subsequently, all patients showed either acute motor axonal neuropathy pattern or reversible conduction failure. CONCLUSION: Serial neurophysiology suggests that C. jejuni infections are exclusive to axonal GBS. SIGNIFICANCE: Our findings suggest that AMAN can demonstrate the full complement of demyelinating features at the early stages of disease.

T cell response in acute motor axonal neuropathy.

There is evidence that in the acute axonal motor neuropathy (AMAN) subtype of Guillain-Barré syndrome antibodies to gangliosides, produced through molecular mimicry by antecedent Campylobacter jejuni (C. jejuni) infection, attack gangliosides expressed in human peripheral nerve axolemma, inducing a primary axonal damage. The aim of this study is to investigate whether the T cell response has a role in AMAN pathogenesis. We isolated monocytes from 4 healthy subjects and 5 AMAN patients with antecedent C. jejuni infection and antibodies to GM1 and/or GD1a gangliosides. Immature dendritic cells expressing CD1 molecules cultured with autologous T cells were stimulated with 2 lipopolysaccharides (LPSs) extracted from C. jejuni strains containing GM1 and GD1a-like structures and with GM1 and GD1a. The T cell response to LPSs and to gangliosides was determined by measuring the release of IFN-gamma and TNF-alpha. We observed a T cell response to both LPSs in controls and AMAN patients, whereas only AMAN patients showed T cell reactivity to gangliosides GM1 and GD1a with a tight correlation between T cell reactivity to the ganglioside and individual antibody responses to the same ganglioside. T cells responding to gangliosides were CD1c-restricted CD8 positive and CD27 negative. These findings indicate a contribution of cellular immunity in the pathogenesis of AMAN. A possible role for ganglioside-reactive T cells might be to facilitate the production of antibodies against gangliosides.

Axonal transport of Listeria monocytogenes and nerve-cell-induced bacterial killing.

Listeria monocytogenes (L. monocytogenes) can cause fatal brainstem encephalitis in both sheep and humans. Here we review evidence that the bacteria can be incorporated into axons following a primary cycle of replication in macrophages/dendritic cells after subcutaneous injection in projection areas of peripheral neurons. The molecular mechanisms for the rocketing of L. monocytogenes in the cytosol by asymmetric cometic tails and the utility of this phenomenon for bacterial migration intraaxonally both in retro- and in anterograde directions to reach the central nervous system are described. The role of the immune response in the control of L. monocytogenes spread through peripheral neurons is highlighted, and a mechanism by which bacteria may be killed inside infected neurons through a nitric oxide-dependent pathway is pointed out.

Contact-dependent demyelination by Mycobacterium leprae in the absence of immune cells.

Demyelination results in severe disability in many neurodegenerative diseases and nervous system infections, and it is typically mediated by inflammatory responses. Mycobacterium leprae, the causative organism of leprosy, induced rapid demyelination by a contact-dependent mechanism in the absence of immune cells in an in vitro nerve tissue culture model and in Rag1-knockout (Rag1-/-) mice, which lack mature B and T lymphocytes. Myelinated Schwann cells were resistant to M. leprae invasion but undergo demyelination upon bacterial attachment, whereas nonmyelinated Schwann cells harbor intracellular M. leprae in large numbers. During M. leprae-induced demyelination, Schwann cells proliferate significantly both in vitro and in vivo and generate a more nonmyelinated phenotype, thereby securing the intracellular niche for M. leprae.

Evidence for intraaxonal spread of Listeria monocytogenes from the periphery to the central nervous system.

Rhombencephalitis due to Listeria monocytogenes is characterized by progressive cranial nerve palsies and subacute inflammation in the brain stem. In this paper, we report observations made on mice infected with L. monocytogenes. Unilateral inoculation of bacteria into facial muscle, or peripheral parts of a cranial nerve, induced clinical and histological signs of mainly ipsilateral rhombencephalitis. Similarly, unilateral inoculation of bacteria into lower leg muscle or peripheral parts of sciatic nerve was followed by lumbar myelitis. In these animals, intraaxonal bacteria were seen in the sciatic nerve and its corresponding nerve roots ipsilateral to the bacterial application site. Development of myelitis was prevented by transsection of the sciatic nerve proximally to the hindleg inoculation site. Altogether, our results support the hypothesis that Listeria rhombencephalitis is caused by intraaxonal bacterial spread from peripheral sites to the central nervous system.

Role of the cell wall phenolic glycolipid-1 in the peripheral nerve predilection of Mycobacterium leprae.

The cell wall of pathogenic mycobacteria is abundant with complex glycolipids whose roles in disease pathogenesis are mostly unknown. Here, we provide evidence for the involvement of the specific trisaccharide unit of the phenolic glycolipid-1 (PGL-1) of Mycobacterium leprae in determining the bacterial predilection to the peripheral nerve. PGL-1 binds specifically to the native laminin-2 in the basal lamina of Schwann cell-axon units. This binding is mediated by the alpha(2LG1, alpha2LG4, and alpha2LG5 modules present in the naturally cleaved fragments of the peripheral nerve laminin alpha2 chain, and is inhibited by the synthetic terminal trisaccharide of PGL-1. PGL-1 is involved in the M. leprae invasion of Schwann cells through the basal lamina in a laminin-2-dependent pathway. The results indicate a novel role of a bacterial glycolipid in determining the nerve predilection of a human pathogen.

Rat dorsal root ganglia neurons as a model for Listeria monocytogenes infections in culture.

Neurotropism of Listeria monocytogenes was studied in rat dorsal root ganglia (DRG) and hippocampal neurons in culture. Using a system in which the DRG neurons can grow relatively free from other cells, it was observed that such DRG neurons, in contrast to hippocampal neurons, can be effectively infected by L. monocytogenes. The bacteria aligned along DRG axons, but not along hippocampal neurites. A mutant deficient in internalin, a protein required for entry into E-cadherin-expressing cells, did not interact with DRG neurons. Axonal migration of bacteria was studied in the DRG neurons grown in a double-chamber system, where either the neurites or the nerve cell bodies were exposed to the bacteria. The data suggest that L. monocytogenes can infect both axons and DRG nerve cell bodies, and that the bacteria can migrate in a retrograde as well as anterograde direction. These results support the notion that L. monocytogenes can spread via primary sensory neurons to the central nervous system. Infection of DRG primary sensory neurons, as employed in the present study, provides a model for analysis of bacterial and neuronal factors of importance for neurovirulence of L. monocytogenes.

Campylobacter species and Guillain-Barré syndrome.

Since the eradication of polio in most parts of the world, Guillain-Barré syndrome (GBS) has become the most common cause of acute flaccid paralysis. GBS is an autoimmune disorder of the peripheral nervous system characterized by weakness, usually symmetrical, evolving over a period of several days or more. Since laboratories began to isolate Campylobacter species from stool specimens some 20 years ago, there have been many reports of GBS following Campylobacter infection. Only during the past few years has strong evidence supporting this association developed. Campylobacter infection is now known as the single most identifiable antecedent infection associated with the development of GBS. Campylobacter is thought to cause this autoimmune disease through a mechanism called molecular mimicry, whereby Campylobacter contains ganglioside-like epitopes in the lipopolysaccharide moiety that elicit autoantibodies reacting with peripheral nerve targets. Campylobacter is associated with several pathologic forms of GBS, including the demyelinating (acute inflammatory demyelinating polyneuropathy) and axonal (acute motor axonal neuropathy) forms. Different strains of Campylobacter as well as host factors likely play an important role in determining who develops GBS as well as the nerve targets for the host immune attack of peripheral nerves. The purpose of this review is to summarize our current knowledge about the clinical, epidemiological, pathogenetic, and laboratory aspects of campylobacter-associated GBS.

Axonal transport of herpes simplex virions to epidermal cells: evidence for a specialized mode of virus transport and assembly.

To examine the transmission of herpes simplex virus (HSV) from axon to epidermal cell, an in vitro model was constructed consisting of human fetal dorsal root ganglia cultured in the central chamber of a dual-chamber tissue culture system separated from autologous skin explants in an exterior chamber by concentric steel cylinders adhering to the substratum through silicon grease and agarose. Axons grew through the agarose viral diffusion barrier and terminated on epidermal cells in the exterior chamber. After inoculation of HSV onto dorsal root ganglia, anterograde axonal transport of glycoprotein and nucleocapsid antigen was observed by confocal microscopy to appear in exterior chamber axons within 12 h and in epidermal cells within 16 h, moving at 2-3 mm/h. Although both enveloped and unenveloped nucleocapsids were observed in the neuronal soma by transmission electron microscopy, only nucleocapsids were observed in the axons, closely associated with microtubules. Nodule formation at the surface of HSV-infected axons, becoming more dense at the axon terminus on epidermal cells, and patches of axolemmal HSV glycoprotein D expression were observed by scanning (immuno)electron microscopy, probably representing virus emerging from the axolemma. These findings strongly suggest a specialized mode of viral transport, assembly, and egress in sensory neurons: microtubule-associated intermediate-fast anterograde axonal transport of unenveloped nucleocapsids with separate transport of glycoproteins to the distal regions of the axon and assembly prior to virus emergence at the axon terminus.

Rabies and borna disease. A comparative pathogenetic study of two neurovirulent agents.

BACKGROUND: Rabies and Borna disease viruses have been regarded as classical neurotropic agents. Many pathogenetic similarities are shared by these two negative strand RNA viruses. In view of recently gained data on the virology and pathology of these two diseases, and up-to-date comparative pathogenetic study seems to be justified. EXPERIMENTAL DESIGN: This study is based on a survey of experimental and natural infections of laboratory animals and natural hosts. The morphologic damage to the nervous system has been evaluated by light and electron microscopy, with special emphasis on immunocytochemical methods. RESULTS: This comparative study disclosed that both viruses are transported inside axons, pass synapses and propagate along neuronal networks. At the sites of synaptic transfer, full virus particles can never be detected in the early phase of rabies virus infection; in Borna disease virus (BDV) infection, virus particles cannot be found in any phase of disease progression. Thus, a major difference exists between the two agents insofar as rabies virus is morphologically well characterized, whereas BDV has never been visualized in tissue sections. Furthermore, rabies virus infects only neurons, whereas BDV also infects glial cells. The host range and the scale of infection of extraneural tissues by both agents is extremely similar. CONCLUSIONS: These observations allow us to postulate that the synaptic transfer of both viruses likely ensures in the form of bare nucleocapsids (ribonucleoprotein-transcriptase complexes). While in the later phases of replication complete rabies virions are regularly assembled, BDV propagates within the central nervous system in an incomplete form, so that it remains morphologically imperceptible. Thus, BDV may appear in a complete, enveloped form only when exiting the host organism. The dissemination patterns of the two agents may be influenced by specific affinities to neurotransmitter receptor sites. It remains unresolved, why BDV readily infects non-neuronal central nervous system cells, while rabies virus remains restricted to neuronal elements.

Demonstration of Treponema pallidum in axons of cutaneous nerves in experimental chancres of rabbits.

After cutaneous inoculation of viable Treponema pallidum subsp pallidum into the skin of chancre-immune or previously uninfected rabbits, organisms move from perivascular connective tissue to localize extracellularly in hair follicles, erector pili muscles, and cutaneous nerves. Large numbers of intact organisms can be seen within the perineurium using electron microscopy, and after extensive sampling a few organisms can be detected within the axon cytoplasm. These findings support the concept that T. pallidum may be able to pass along the nerve fibers to the central nervous system.

Axonal-transsynaptic spread as the basic pathogenetic mechanism in B virus infection of the nervous system.

An experimental study on the pathogenesis of B virus infection in the mouse has documented that the agent spreads in an axonal-transsynaptic manner in the nervous system. The characteristics of the spread of B virus are similar to those of other members of the herpes virus group.

Axonal and transsynaptic (transneuronal) spread of Herpesvirus simiae (B virus) in experimentally infected mice.

In order to study the pathogenesis of B virus infection of the nervous system, newborn and young mice were inoculated by four different routes: 1. Intramuscular (i.m.) in the forelimb; 2. I.m. in the hindlimb; 3. Subcutaneous (s.c.) in the abdominal wall; 4. Intraperitoneal (i.p.). Spread of virus was followed by immunohistochemical demonstration of viral antigen in tissue sections of the peripheral and central nervous system. Three distinct patterns emerged: 1. After i.m. limb inoculations, virus progressed along the ipsilateral dorsal column, the bilateral spinothalamic and bilateral spinoreticular systems and along central autonomic pathways. 2. After s.c. inoculation, the dorsal column was spared, otherwise the spread was similar to that following i.m. inoculations. 3. After i.p. inoculation, virus spread in the spinal cord bilaterally, mainly along spinothalamic and central autonomic pathways. The peripheral motoneurons were conspicuously spared, even in the i.m. inoculation mode. In the brain stem, B virus antigen appeared bilaterally, at multiple sites. In the cerebrum, virus infected cells appeared first in the thalamus, hypothalamus and the motor cortex. The mode of spread from spinal levels was mainly orthograde along the ascending systems (dorsal columns, spinothalamic, spinoreticular tracts), but also retrograde along descending systems (pyramidal tract, central autonomic pathways). Oligosynaptic systems transmitted virus more quickly than the polysynaptic ones. In the involvement of various neuronal systems in virus spread, a certain selectivity, sparing the peripheral motoneuron and the cerebellar systems, could be assessed.