Myelin breakdown favours Mycobacterium leprae survival in Schwann cells.

Leprosy neuropathy is a chronic degenerative infectious disorder of the peripheral nerve caused by the intracellular obligate pathogen Mycobacterium leprae (M. leprae). Among all nonneuronal cells that constitute the nerve, Schwann cells are remarkable in supporting M. leprae persistence intracellularly. Notably, the success of leprosy infection has been attributed to its ability in inducing the demyelination phenotype after contacting myelinated fibres. However, the exact role M. leprae plays during the ongoing process of myelin breakdown is entirely unknown. Here, we provided evidence showing an unexpected predilection of leprosy pathogen for degenerating myelin ovoids inside Schwann cells. In addition, M. leprae infection accelerated the rate of myelin breakdown and clearance leading to increased formation of lipid droplets, by modulating a set of regulatory genes involved in myelin maintenance, autophagy, and lipid storage. Remarkably, the blockage of myelin breakdown significantly reduced M. leprae content, demonstrating a new unpredictable role of myelin dismantling favouring M. leprae physiology. Collectively, our study provides novel evidence that may explain the demyelination phenotype as an evolutionarily conserved mechanism used by leprosy pathogen to persist longer in the peripheral nerve.

Myelin breakdown favours Mycobacterium leprae survival in Scwann cells

Leprosy neuropathy is a chronic degenerative infectious disorder of the peripheral nerve caused by the intracellular obligate pathogen Mycobacterium leprae (M. leprae). Among all nonneuronal cells that constitute the nerve, Schwann cells are remarkable in supporting M. leprae persistence intracellularly. Notably, the success of leprosy infection has been attributed to its ability in inducing the demyelination phenotype after contacting myelinated fibres. However, the exact role M. leprae plays during the ongoing process of myelin breakdown is entirely unknown. Here, we provided evidence showing an unexpected predilection of leprosy pathogen for degenerating myelin ovoids inside Schwann cells. In addition, M. leprae infection accelerated the rate of myelin breakdown and clearance leading to increased formation of lipid droplets, by modulating a set of regulatory genes involved in myelin maintenance, autophagy, and lipid storage. Remarkably, the blockage of myelin breakdown significantly reduced M. leprae content, demonstrating a new unpredictable role of myelin dismantling favouring M. leprae physiology. Collectively, our study provides novel evidence that may explain the demyelination phenotype as an evolutionarily conserved mechanism used by leprosy pathogen to persist longer in the peripheral nerve.

Microbiota influence the development of the brain and behaviors in C57BL/6J mice.

We investigated the contributions of commensal bacteria to brain structural maturation by magnetic resonance imaging and behavioral tests in four and 12 weeks old C57BL/6J specific pathogen free (SPF) and germ free (GF) mice. SPF mice had increased volumes and fractional anisotropy in major gray and white matter areas and higher levels of myelination in total brain, major white and grey matter structures at either four or 12 weeks of age, demonstrating better brain maturation and organization. In open field test, SPF mice had better mobility and were less anxious than GF at four weeks. In Morris water maze, SPF mice demonstrated better spatial and learning memory than GF mice at 12 weeks. In fear conditioning, SPF mice had better contextual memory than GF mice at 12 weeks. In three chamber social test, SPF mice demonstrated better social novelty than GF mice at 12 weeks. Our data demonstrate numerous significant differences in morphological brain organization and behaviors between SPF and GF mice. This suggests that commensal bacteria are necessary for normal morphological development and maturation in the grey and white matter of the brain regions with implications for behavioral outcomes such as locomotion and cognitive functions.

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.

Experimental feeding of Hydrilla verticillata colonized by stigonematales cyanobacteria induces vacuolar myelinopathy in painted turtles (Chrysemys picta).

Vacuolar myelinopathy (VM) is a neurologic disease primarily found in birds that occurs when wildlife ingest submerged aquatic vegetation colonized by an uncharacterized toxin-producing cyanobacterium (hereafter "UCB" for "uncharacterized cyanobacterium"). Turtles are among the closest extant relatives of birds and many species directly and/or indirectly consume aquatic vegetation. However, it is unknown whether turtles can develop VM. We conducted a feeding trial to determine whether painted turtles (Chrysemys picta) would develop VM after feeding on Hydrilla (Hydrilla verticillata), colonized by the UCB (Hydrilla is the most common "host" of UCB). We hypothesized turtles fed Hydrilla colonized by the UCB would exhibit neurologic impairment and vacuolation of nervous tissues, whereas turtles fed Hydrilla free of the UCB would not. The ability of Hydrilla colonized by the UCB to cause VM (hereafter, "toxicity") was verified by feeding it to domestic chickens (Gallus gallus domesticus) or necropsy of field collected American coots (Fulica americana) captured at the site of Hydrilla collections. We randomly assigned ten wild-caught turtles into toxic or non-toxic Hydrilla feeding groups and delivered the diets for up to 97 days. Between days 82 and 89, all turtles fed toxic Hydrilla displayed physical and/or neurologic impairment. Histologic examination of the brain and spinal cord revealed vacuolations in all treatment turtles. None of the control turtles exhibited neurologic impairment or had detectable brain or spinal cord vacuolations. This is the first evidence that freshwater turtles can become neurologically impaired and develop vacuolations after consuming toxic Hydrilla colonized with the UCB. The southeastern United States, where outbreaks of VM occur regularly and where vegetation colonized by the UCB is common, is also a global hotspot of freshwater turtle diversity. Our results suggest that further investigations into the effect of the putative UCB toxin on wild turtles in situ are warranted.

Molecular mimicry in infectious encephalitis and neuritis: binding of antibodies against infectious agents on Western blots of human nervous tissue.

OBJECTIVES: To study the occurrence of cross-reactivities of antibodies against infectious agents with human nervous tissue. METHODS: Binding of 25 antibodies against 17 neurotropic pathogens comprising Borrelia burgdorferi, Toxoplasma gondii, and various DNA and RNA viruses to Western blots of human cortex and myelin from central and peripheral nervous system was investigated. RESULTS: Fourteen of the 25 antibodies tested showed binding to Western blots of human nervous tissue, suggesting the presence of shared epitopes. Binding of 11 antibodies against 10 pathogens to cortex and/or myelin correlated with the tissue targeted by neuropathological lesions. Three antibodies did not show such correlation; 11 antibodies did not bind at all. CONCLUSIONS: Our results suggest that shared epitopes between infectious agents and human nervous tissues are more common than previously expected. Thus, molecular mimicry should be considered more frequently as a possible pathogenetic mechanism, among others, inducing tissue damage in encephalitis and neuritis caused by various pathogens.

Unilateral optic neuritis caused by Histoplasma capsulatum in a patient with the acquired immunodeficiency syndrome.

PURPOSE: To evaluate the potential of Histoplasma capsulatum to cause optic neuritis in the setting of the acquired immunodeficiency syndrome (AIDS). METHODS: We examined a 35-year-old man with a history of AIDS and disseminated histoplasmosis who developed a unilateral progressive optic neuritis of enigmatic origin. An optic nerve sheath biopsy was performed to provide a tissue diagnosis. RESULTS: Histoplasma capsulatum was identified in both the optic nerve sheath and fungal culture. CONCLUSION: Histoplasma capsulatum should be considered in the differential diagnosis of optic neuritis in patients with AIDS, even in the absence of chorioretinal findings.

Dorsal root ganglia may be reservoirs of viral infection in multiple sclerosis.

There are presently two competitive theories that attempt to explain the etiology of multiple sclerosis (MS). Briefly summarized, they are: 1. An infection, probably of viral type, may attack the oligodendroglia of the central nervous system; or, 2. An autoimmune process may begin with an infection of the peripheral lymphatic immune system, producing antibodies that cross the blood-brain barrier, leading to myelinoclasia. Since 1935, research has been directed toward myelin of the central nervous system and the myelin sheaths of peripheral nerve; however, dorsal root and cranial sensory ganglia (DRG) have apparently not been studied. The present hypothesis states that an infectious agent (probably viral) finds privileged sanctuary in the dorsal root and cranial sensory ganglia (DRG): thereafter periodically invading the spinal cord, brain, or peripheral nerve. Previously reported erratic spinal fluid viral titers and cultures can be explained by differences in the anatomy of the DRG in which there is a variable and limited contact of spinal fluid with sensory ganglia. Clues to this hypothesis were noted by the author during routine neurological examinations of patients with MS, in which sensory signs and symptoms were frequently encountered. This clinical observation has also been reported by others who found such symptoms in 75% of MS patients, ranking second only to incoordination.

Reaction of peripheral nerves to vascular and bacterial injuries.

Mouse sciatic nerves were subjected to devascularization, M. leprae inoculation, and combined insult of devascularization + footpad inoculation (FPI). Changes were seen in FPI nerves only after eight months, but in cases of combined insult, changes were evident in hours. Both the groups showed initial loss of small myelinated fibres. No proliferation of Schwann cells was in FPI nerves, but in combined insult it was maximum after two weeks. Presence of M. leprae seems to be arresting Schwann cell activity after two weeks. Blood vessels showed increased endothelial cell cytoplasm, basement membrane proliferation and villi formation. These changes seem to be specific of endoneurial blood vessels of leprosy nerves. Increased number of mast cells seems to be specific of devascularized and FPI nerves. Increased number of macrophages expressed low immunity of devascularized nerves. Eosinophils migrated to endoneurium as a result of leakage of axoplasm.

West Nile virions aligned along myelin lamellae in organotypic spinal cord cultures.

Organotypic spinal cord cultures infected with West Nile Virus (WNV) exhibited a remarkable arrangement of virions among lamellae of the myelin sheath. Virions were first observed in neurons and only at day 4 after infection appeared within the myelin lamellae. Virions were observed only in the central myelin, aligned along the interperiod lines and therefore attached to the outer side of the oligodendrocyte membrane. In spite of this peculiar location of the virions, their presence was not associated with severe damage to the axon or to the myelin sheath. The causes of the formation of this viral pattern, its morphological features, and the role which it might have in viral infection in vivo are considered.

Observations on demyelinating lesions induced by Theiler's virus in CBA mice.

We examined demyelinating lesions in the spinal cord of CBA mice infected with the BeAn strain of Theiler's virus to see if it was possible to document the sequence of changes which result in demyelination. It was found that the lesions which develop in the late stages of the disease were progressive. Therefore, by examining the different zones of a single lesion, it was possible to follow a sequence of changes which lead to demyelination. There was a clear progression from normal myelin, to vacuolated myelin, to myelin phagocytosis, to demyelinated axons, to remyelinated axons. Virus was detected in degenerating oligodendrocytes in the area showing myelin vacuolation by both electron microscopy and immunocytochemistry, a finding which indicated that virus infection precedes demyelination. The area of normal myelin which surrounded the zone of vacuolated myelin was infiltrated by lymphocytes, indicating that lymphocytic infiltration preceded viral replication and oligodendrocyte degeneration. Our observations indicate that cells of the immune system may play a role in the initiation of virus replication which appears to be a prerequisite for demyelination.

HTLV-III-like particles within a cell process surrounded by a myelin sheath in an AIDS brain.

HTLV-III-like particles were observed within a cell process surrounded by a myelin sheath, in the brain of a 4-year-old boy with AIDS encephalopathy. Similar particles were also observed in the mononuclear macrophage-like cells.

The pathogenicity of the A7, M9 and L10 strains of Semliki Forest virus for weanling mice and primary mouse brain cell cultures.

The multiplication of the M9, A7 and L10 strains of Semliki Forest virus (SFV), both in weanling mice and primary mouse brain cell cultures, was compared. Following both intraperitoneal (i.p.) and intracerebral (i.c.) injection, the virulent L10 strain multiplied to higher titre in the mouse central nervous system (CNS) than did the less virulent M9 and A7 strains, whereas M9 multiplied to higher titre than A7. By the i.c. route, all three virus strains multiplied to higher titre than following i.p. injection. Multiplication of A7 and M9 in oligodendrocytes, but not neurons, was detected following i.c. injection. All three virus strains showed a tropism for cultured mouse glial cells rather than neurons. The L10 strain multiplied better in neurons than did A7 or M9. It is concluded that the mechanism of acute demyelination induced by the M9 and A7 strains is similar. Based on this and previous studies, it is proposed that infection of glial cells triggers immune-mediated demyelination. The virulence of the L10 strain is due to its ability to exceed a lethal threshold of damage to neurons before immune intervention can occur.

Viruses and demyelinating disease of the central nervous system.

In MS, there are many mechanisms by which viruses can produce demyelinating diseases in humans and experimental demyelinating infections in animals.

The incubation period of multiple sclerosis.

Movement of myelin through the spiral laminar arrangement of the myelin sheaths of neurones might act as a biological clock in determining the prolonged incubation period of multiple sclerosis. A defect incorporated peripherally in the myelin sheath as a result of neonatal virus infection might be revealed years later when the defective myelin reaches the axolemma and provokes an immunological reaction. This process could, directly or indirectly, be prevented by the effects of solar radiation, thus accounting for the geographical distribution of the disease.

[Viral hypothesis of multiple sclerosis: new aspects]. / Hypothèse virale de la sclérose en plaques: nouveaux aspects.

A review is presented of the epidemiological and serological data on which the viral hypothesis of multiple sclerosis is based. Recent experiments investigating the capacity of viruses to establish chronic infections are presented as a model to explain the clinical course of the disease. Finally, studies of the molecular interactions of vaccinia virus with the myelin membrane serve as a basis on which to discuss the problem of the mechanism of demyelination.

Herpes simplex virus types 1 and 2 in organotypic cultures of mouse central and peripheral nervous system. 2. Electron microscopic observations of myelin degeneration.

Organotypic cultures of mouse spinal cord with attached dorsal root ganglia, which contain both central and peripheral myelin in the one unit of tissue, were infected with HSV 1 or HSV 2 and studied using electron microscopy. Intranuclear viral nucleocapsids and intracytoplasmic enveloped particles were found in the Schwann cells associated with peripheral myelin and in oligodendroglia associated with central myelin. Degeneration of peripheral myelin most commonly involved an asymmetrical swelling of the myelin lamellae, whereas degeneration of central myelin was characterized by a more generalized swelling resulting in separation of the myelin lamellae. Degeneration of both central and peripheral myelin was found in the presence of intact axons which were indistinguishable from those in controls.

Mouse hepatitis virus-induced recurrent demyelination. A preliminary report.

Four-week-old BALB/c mice inoculated intracerebrally with the JHM strain of mouse hepatitis virus developed an acute demyelinating disease followed by apparent recovery with remyelination. When surviving mice were examined 16 months later, small areas of active demyelination were still present. This is the first reported example, to our knowledge, of an experimental viral infection in which acute demyelination with recovery is followed by persisting or recurring demyelination.