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Thread: Immune cell plays good cop, bad cop

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    Senior Member Max's Avatar
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    Immune cell plays good cop, bad cop

    Immune cell plays good cop, bad cop

    Web edition : Tuesday, September 16th, 2008
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    Depending on where a neuron is injured, immune cells can either help or harm
    Talk about a mixed blessing. A pair of new studies shows that immune cells known as macrophages can do an injured neuron good, or can impart further harm. As the real estate axiom about location predicts, the outcome partly depends on where the neuron is injured. A neuron that controls motion or feeling starts out in the brain, runs down the spinal cord and eventually connects with muscles, skin or other organs.
    If the neuron is wounded in the portion located in the brain or spinal cord (known as the central nervous system) macrophages can prevent regeneration, a new study in the Sept. 17 Journal of Neuroscience shows. But if the injury occurs in other parts of the body (the peripheral nervous system) macrophages help heal the hurt, a second study in the same issue of the journal demonstrates.
    Although a single neuron traverses the central nervous system and ends up in the peripheral nervous system, conditions between the two are very different. “We’re really talking about two different biologies,” says Jerry Silver, a neuroscientist from Case Western Reserve University in Cleveland who led one of the studies.
    Injured neurons regenerate by reconnecting long projections called axons to the muscles, nerves or other organs to which the axons were originally attached. Macrophages can either help axons regrow or can attack, causing the neuron to retract the axon, the studies show.
    “Those are seemingly contradictory results, but they’re really not,” says Phillip G. Popovich, a neuroimmunologist at Ohio State University in Columbus. He was not involved in either study, but for many years has investigated the role immune cells play in regenerating nerve cells. “People like to think of these as black and white responses, but it’s not that simple.”
    http://www.sciencenews.org/view/gene...d_cop,_bad_cop

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    Senior Member Max's Avatar
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    Arrow News tips from the Journal of Neuroscience

    News tips from the Journal of Neuroscience

    1. Macrophages Can Promote Regeneration
    Benoit Barrette, Marc-André Hébert, Mohammed Filali, Kathleen Lafortune, Nicolas Vallières, Geneviève Gowing, Jean-Pierre Julien, and Steve Lacroix
    The role of macrophages in recovery from nerve injury is controversial. Some studies show that macrophages improve regeneration, but others show the opposite effect. This week, each side of the controversy gains support. After crushing a peripheral nerve in mice, Barrette et al. locally depleted myeloid white blood cells (both granulocytes and macrophages) that expressed a specific protein. This reduced axonal regeneration and functional recovery. Depletion of myeloid cells in peripheral nerve grafts, which normally permit some regeneration of spinal axons, rendered the grafts unable to support such growth. Additional experiments suggested that myeloid cells normally enhance regeneration by clearing myelin debris (which is likely to contain growth-inhibiting molecules), secreting growth-promoting neurotrophic factors (likely from granulocytes, rather than macrophages), and stimulating the growth of new blood vessels, which axons often grow along as they regenerate.
    2. But Macrophages Can Also Hinder Regeneration
    Kevin P. Horn, Sarah A. Busch, Alicia L. Hawthorne, Nico van Rooijen, and Jerry Silver
    In contrast to Barrette et al. (above), Horn al. report that macrophages may hinder regeneration in the spinal cord of rats by promoting axonal retraction. Central nervous system axons normally retract from a site of injury. To examine the role of macrophages in this process, Horn et al. specifically targeted phagocytic cells with toxin enclosed in liposomes. Depleting macrophages after a spinal cord crush did not affect the initial retraction of injured axons, but prevented later retraction that normally occurs after macrophages invade the spinal cord. In vitro studies on dorsal root ganglion neurons revealed that when an activated macrophage contacts a dystrophic axon, the macrophage adheres to and tugs on the axon, pulling it from the substrate and causing retraction. Together, these two studies suggest that whether myeloid cells help or hinder axon regeneration may depend on what type of myeloid cells are present (i.e., what subtypes of macrophages and granulocytes) and where and how macrophages are activated (e.g., by peripheral or CNS cues). Many macrophages (green) but few astrocytes (blue) were present at a lesion site 7 d after nerve crush (left). Treatment with toxic liposomes greatly reduced the number of macrophages, but astrocytes remained. See the article by Horn et al. for details.




    http://www.eurekalert.org/pub_releas...-ntf091008.php

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