Human nerve growth factor protects common marmosets against autoimmune encephalomyelitis by switching the balance of T helper cell type 1 and 2 cytokines within the central nervous system

Abstract

Multiple sclerosis is a demyelinating disorder of the central nervous system (CNS), in which an immune attack directed against myelin constituents causes myelin destruction and death of oligodendrocytes, the myelin-producing cells. Here, the efficacy of nerve growth factor (NGF), a growth factor for neurons and oligodendrocytes, in promoting myelin repair was evaluated using the demyelinating model of experimental allergic encephalomyelitis (EAE) in the common marmoset. Surprisingly, we found that NGF delayed the onset of clinical EAE and, pathologically, prevented the full development of EAE lesions. We demonstrate by immunocytochemistry that NGF exerts its antiinflammatory effect by downregulating the production of interferon gamma by T cells infiltrating the CNS, and upregulating the production of interleukin 10 by glial cells in both inflammatory lesions of EAE and normal-appearing CNS white matter. Thus, NGF, currently under investigation in human clinical trials as a neuronal trophic factor, may be an attractive candidate for therapy of autoimmune demyelinating disorders.

Figure 1

Representative neuropathological findings in placebo- (A) and rhNGF-treated (B) animals at the completion of the study (day 28 after immunization). Gross anatomical views of coronal sections through the temporal lobe illustrate multiple demyelinating plaques disseminated throughout the subcortical white matter in the control. In the rhNGF-treated animal, the density of plaques is markedly reduced. The paraffin-embedded sections were stained with Luxol Fast blue/periodic acid-Schiff.

Figure 2

Characterization of NGF receptors in marmoset brain by immunohistochemistry. Staining for TrkA is shown at the left (5-μm paraffin-embedded section), and for p75^NGFR at the right (30-μm-thick section stained in flotation). (A) Both NGF receptors are present in cholinergic neurons of the basal forebrain. Arrows show satellite oligodendrocytes stained for TrkA (left). (B) Arrows indicate some of the TrkA- and p75^NGFR-positive glial cells (astrocytes or microglia) in normal white matter. (C) In CNS inflammatory infiltrates, strong staining for both NGF receptors is also apparent on many mononuclear cells and macrophages (arrows). Original magnifications: ×400.

Figure 3

Serial measurements of T cell and antibody reactivity against MOG during the course of EAE in placebo- and rhNGF-treated marmosets. (A) MOG-specific T cell proliferative responses in marmoset PBMCs at days 0, 14, and 28 after immunization. (B) Serum anti-MOG antibody titers measured by ELISA at day 28 after immunization. The differences between placebo- and rhNGF-treated animals were not statistically significant.

Figure 4

Effects of rhNGF on cytokine production within the CNS of nonhuman primates. Representative sections from placebo-treated (left) and rhNGF-treated (right) marmosets. (A and B) Staining for IFN-γ demonstrates the presence of this cytokine in inflammatory mononuclear cells in the center of a perivascular infiltrate from a placebo-treated animal (some designated by arrows); complete suppression is evident in an infiltrate from an rhNGF-treated animal. (C and D) Staining for IL-10, demonstrating strong upregulation of this cytokine in astrocytes of the corpus callosum (normal white matter) in an rhNGF-treated animal. Original magnifications: ×400.