Endogenous antibodies promote rapid myelin clearance and effective axon regeneration after nerve injury

Abstract

Degenerating myelin inhibits axon regeneration and is rapidly cleared after peripheral (PNS) but not central nervous system (CNS) injury. To better understand mechanisms underlying rapid PNS myelin clearance, we tested the potential role of the humoral immune system. Here, we show that endogenous antibodies are required for rapid and robust PNS myelin clearance and axon regeneration. B-cell knockout JHD mice display a significant delay in macrophage influx, myelin clearance, and axon regeneration. Rapid clearance of myelin debris is restored in mutant JHD mice by passive transfer of antibodies from naïve WT mice or by an anti-PNS myelin antibody, but not by delivery of nonneural antibodies. We demonstrate that degenerating nerve tissue is targeted by preexisting endogenous antibodies that control myelin clearance by promoting macrophage entrance and phagocytic activity. These results demonstrate a role for immunoglobulin (Ig) in clearing damaged self during healing and suggest that the immune-privileged status of the CNS may contribute to failure of CNS myelin clearance and axon regeneration after injury.humoral immunity | nerve regeneration D uring the process of wound healing, rapid and efficient clearance of cellular debris is necessary for tissue regeneration (1). Myelin debris remains in white matter tracks years after an injury to the CNS in humans and primates (2, 3). The prolonged presence of myelin-associated inhibitors of axon regeneration is thought to contribute to the lack of recovery following CNS injury. Although peripheral myelin also contains inhibitors of axon regeneration, PNS myelin is rapidly cleared after injury, thereby permitting rapid axon regeneration (4-6). It is not known why the rates of clearance of PNS and CNS are so different (7).Antibodies, like other opsonins, coat exogenous debris and pathogens, thereby targeting them for clearance by phagocytes. The recognition of self antigens by natural antibodies produced by B1 cells is well documented (8). Although it is hypothesized that these antibodies may have a physiological role other than immune defense, their role in clearing necrotic cellular debris is not known (8). Therefore, we tested whether endogenous antibodies contribute to rapid removal of degenerating myelin after PNS injury, thereby promoting axon regeneration. ResultsAntibodies Accumulate in Sciatic Nerve After Injury. To investigate whether endogenous antibodies aid in removal of myelin debris, we first examined whether antibodies accumulate in peripheral nerves following injury. We compared nerve injury responses between WT and JHD mice, which have a targeted deletion of the JH locus that prevents VDJ recombination and the formation of mature B-cells and antibodies (9). Control and crushed sciatic nerves were obtained from WT and JHD mice and stained with anti-mouse Ig antibodies. Six days after crush injury, we observed a strong increase in immunoreactivity for Ig on degenerating myelin sheathes distal to the site of injury in WT but not in JHD nerves (Fig. S1A). To ...

B-Cell Maturation Antigen, A Proliferation-Inducing Ligand, and B-Cell Activating Factor Are Candidate Mediators of Spinal Cord Injury-Induced Autoimmunity

“…7,18,19 For instance, animal models of multiple sclerosis have demonstrated natural IgM autoantibodies that play a protective role enhancing remyelination and preventing neuronal apoptosis. 20,21 Similarly, mice deficient in mature B cells demonstrated greater neuron survival after intravitreal glutamate injections. 22 This response, however, may depend on other genetic factors, because opposite results were obtained in response to neurological injury in animals of different genetic backgrounds.…”

Phagocytosis of neuronal debris by microglia is associated with neuronal damage in multiple sclerosis

“…That such release of neuronal antigens may be pathogenic has been shown in adoptive transfer of antibodies from mice with spinal cord injury that on intraspinal injection into healthy mice cause hind limb paralysis (Ankeny et al, 2009). Naturally occurring antibodies that distinguish damaged tissue as non-self are required for the rapid and efficient removal of damaged axons and myelin after nerve crush (Vargas et al, 2010). Due to the immune privileged state of the CNS, there may be a failure of this antibody-mediated repair mechanism because naturally occurring antibodies may be unable to cross the blood-brain barrier.…”

Gpr126 is essential for peripheral nerve development and myelination in mammals

“…We used the following primary antibodies: rat-anti-myelin basic protein (1:10, AbD Serotec), rabbit-anti-peripherin (1:100, Millipore Bioscience Research Reagents), goat-anti-Pou3f1 (1:100, Santa Cruz Biotechnology), mouseanti-myelin protein zero (1:1000) (Vargas et al, 2010) and rabbit-antineurofilament-M (1:200, Chemicon). Samples were incubated with appropriate fluorescently labeled secondary antibodies (1:1000, Molecular Probes; 1:200, Jackson ImmunoResearch), visualized by epi-fluorescence microscopy (Zeiss Axioplan2 for sciatic nerves and Zeiss Axioimager for cochleae) and digitally photographed (Zeiss AxioCam).…”