Immunomodulation of cytokine and chemokine production in animal models of neuroinflammatory and neurodegenerative disorders

Abstract

Experimental autoimmune neuritis (EAN) is a CD4+ T cell-mediated autoimmune disease of the peripheral nervous system (PNS) that can be actively induced in susceptible animal species and strains by active immunization with heterogeneous peripheral nerve myelin or its component P2 or PO proteins or their peptides emulsified in Freund's complete adjuvant. EAN represents an animal model for studying the immunopathogenesis and therapy of Guillain-Barré syndrome (GBS ) which is a major inflammatory demyelinating disease of the PNS in humans. The close clinical, histopathological, and electrophysiological similarities between EAN and GBS make EAN an especially suitable model, capable of offering insights into the pathophysiology of GBS. EAN is also considered to represent a general model for studying CD4+-mediated autoimmune diseases.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia in the Western world. It is characterised neuropathologically by the deposition of extracellular amyeloid plaques containing aggregates of the amyloid protein beta (A-beta) peptide, as well as by intracellular aggregation of neurofibrillary tangles and selective neuronal loss accompanied by cerebrovascular amyloidosis. The mechanism of AD has not been completely defined. The inflammatory cytokines have been implicated as mediators in response to brain injury in AD. A-beta precursor protein APP transgenic mice (Tg2576) are one of the most widely used animal model for A-beta plaques in cortical regions of the brain, which over-expresses human APP with the Swedish double mutation.

Peak numbers of macrophage inflammatory protein (MIP)- 1 alpha-positive cells in the sciatic nerve were seen on day 14 post-immunization (p.i.), which coincided with the development of severe clinical signs. Administration of an anti-MIP-1 alpha antibody suppressed clinical signs of EAN and inhibited inflammation and demyelination in the sciatic nerve. Peak numbers of monocyte chemotactic protein (MCP)-1-positive cells in the sciatic nerve were detected on day 7 p.i. (i.e., tile onset of clinical EAN). Administration of an anti-MCP-1 antibody caused a delay of onset of EAR The numbers of MIP-2-positive cells reached a maximum on day 21 p.i. Anti-MIP-2 antibody failed to suppress clinical signs of EAN and inflammation and demyelination in the sciatic nerve.

EAN was strongly suppressed by Rolipram administered twice daily intraperitoneally from day 9 p.i., after onset of clinical EAN, to day 18 p.i., over 10 days. This clinical effect was associated with dose-dependent downregulation of interferon (IFN)-gamma and the chemokines MIP-1alpha, MIP-2 and MCP-1 as well as up-regulated interleukin (IL)-4 production in sciatic nerve sections from Rolipram-treated EAN rats at the maximum of clinical EAN, i.e., on day 14 p.i. These findings suggest that Rolipram could be useful in certain T cell-dependent autoimmune diseases and inflammatory neuropathies.

ABR-215062, which is a new synthetic immunomodulatory compound derived from Linomide, administered daily subcutaneously from the day of inoculation strongly suppressed EAN in a dose-dependent manner. ABR215062 reduced the incidence of EAN, ameliorated clinical signs, and inhibited PO peptide 180-199-specific T and B cell responses and also decreased inflammation and demyelination in the peripheral nerves. The suppression of clinical EAN is associated with inhibition of the inflammatory cytokines IFN-gamma and tumor necrosis factor-alpha as well as the enhancement of the anti-inflammatory cytokine IL-4 in peripheral nerve tissues. The suppressive effects of ABR-215062 on EAN are quite similar to those of Linomide on EAN. These findings suggest that ABR-215062 could be useful in certain T cell-mediated autoimmune diseases.

To elucidate the mechanisms involved in A-beta-mediated inflammation, we used immunocytochemistry and in situ hybridization to study the potential role of the cytokines interferon-gamma (IFN-gamma), interleukin (IL)-12 and IL-4 in transgenic mice Tg2576. Cytokine and cytokine mRNA expression was detected in brain sections from cortical regions at various postnatal ages ranging from 3 to 19 months. High levels of IFN-gamma and IL-12 mRNA expression, as well as their protein production appeared early at 9 months and peaked at 17-19 months in Tg2576 mice. Significantly increased transcripts of IFN-gamma and IL-12 genes were found in the reactive microglia. and astrocytes surrounding AP deposits. Both findings indicate a role for the pro-inflammatory cytokines IFN-gamma and IL-12 in early disease development and are consistent with microglial activation related to AP formation.

In contrast, transcription and production of IL-4 in brain sections was almost undetectable in transgenic mice up to post-natal ages of 17-19 months. These results suggest a major pro-inflammatory role for IL-12 and IFN- gamma in Tg2576 transgenic mice that may provide the association between AP plaque formation, microglial and astrocyte activation in these animals. These observations call for further studies on the potential role of anti-inflammatory therapeutic strategies for AD.