No abstract

Glial neuroinflammation is associated with the development and progression of multiple sclerosis. PET imaging offers a unique opportunity to evaluate neuroinflammatory processes longitudinally in a noninvasive and clinically translational manner. 18 F-PBR111 is a newly developed PET radiopharmaceutical with high affinity and selectivity for the translocator protein (TSPO), expressed on activated glia. This study aimed to investigate neuroinflammation at different phases of relapsing-remitting (RR) experimental autoimmune encephalomyelitis (EAE) in the brains of SJL/J mice by postmortem histologic analysis and in vivo by PET imaging with 18 F-PBR111. Methods: RR EAE was induced by immunization with PLP 139-151 peptide in complete Freund's adjuvant. Naive female SJL/J mice and mice immunized with saline-complete Freund's adjuvant were used as controls. The biodistribution of 18 F-PBR111 was measured in 13 areas of the central nervous system and compared with PET imaging results during different phases of RR EAE. The extents of TSPO expression and glial activation were assessed with immunohistochemistry, immunofluorescence, and a real-time polymerase chain reaction. Results: There was significant TSPO expression in all of the central nervous system areas studied at the peak of the first clinical episode and, importantly, at the preclinical stage. In contrast, only a few TSPO-positive cells were observed at the second episode. At the third episode, there was again an increase in TSPO expression. TSPO expression was associated with microglial cells or macrophages without obvious astrocyte labeling. The dynamics of 18 F-PBR111 uptake in the brain, as measured by in vivo PET imaging and biodistribution, followed the pattern of TSPO expression during RR EAE. Conclusion: PET imaging with the TSPO ligand 18 F-PBR111 clearly reflected the dynamics of microglial activation in the SJL/J mouse model of RR EAE. The results are the first to highlight the discrepancy between the clinical symptoms of EAE and TSPO expression in the brain, as measured by PET imaging at the peaks of various EAE episodes. The results suggest a significant role for PET imaging investigations of neuroinflammation in multiple sclerosis and allow for in vivo follow-up of antiinflammatory treatment strategies.

To examine the complex role of cytokines in the pathogenesis of actively induced murine EAE we measured the levels of a number of cytokines (IL-6, IFN gamma and TNF) in the spinal cord and CSF of mice with active experimental autoimmune encephalomyelitis (EAE) and found them all to be elevated. We next treated mice with antibodies to these three cytokines, which were over expressed in the CNS, to determine if they would alter disease and found the following: anti-IL-6 had no significant effect on disease, anti-IFN gamma exacerbated disease, and anti-TNF either enhanced, had no effect or inhibited EAE depending on the antibody used. We then treated mice with exogenous cytokines, delivered using a recombinant vaccinia virus system, and found that the IL-6 and TNF virus constructs inhibited EAE whereas the IFN gamma construct had no effect on disease. Other cytokine recombinant viruses were also tested and it was found that the IL-1 beta, IL-2 and IL-10 viruses inhibited EAE while an IL-4 virus either had no effect or enhanced disease. We do not know the mechanism of action of the various cytokines in this system, but irrespective of the mechanism(s), this work clearly demonstrates that delivery of select cytokines using recombinant virus-cytokine constructs can provide a powerful means of down-regulating experimental organ-specific autoimmune disease.

Interferon-␥ (IFN␥) is a pleiotropic cytokine that plays an important role in many inflammatory processes, including autoimmune diseases such as multiple sclerosis (MS).Demyelination is a hallmark of MS and a prominent pathological feature of several other inflammatory diseases of the central nervous system, including experimental autoimmune encephalomyelitis, an animal model of MS. Accordingly, in this study we followed the effect of IFN␥ in the demyelination and remyelination process by using an experimental autoimmune encephalomyelitis model of demyelination/remyelination after exposure of mice to the neurotoxic agent cuprizone. We show that demyelination in response to cuprizone is delayed in mice lacking the binding chain of IFN␥ receptor. In addition, IFN␥R ؊/؊ mice exhibited an accelerated remyelination process after cuprizone was removed from the diet. Our results also indicate that the levels of IFN␥ were able to modulate the microglia/macrophage recruitment to the demyelinating areas. Moreover, the accelerated regenerative response showed by the IFN␥R ؊/؊ mice was associated with a more efficient recruitment of oligodendrocyte precursor cells in the demyelinated areas. In conclusion, this study suggests that IFN␥ regulates the development and resolution of the demyelinating syndrome and may be associated with toxic effects on both mature oligodendrocytes and oligodendrocyte precursor cells.

The dynamics in the cuprizone-induced astroglial and TSPO changes, observed by SPECT imaging, were confirmed by immunofluorescence, RT-PCR and autoradiography. The highly specific TSPO radioiodinated ligand CLINDE can be used as an in vivo marker for early detection and monitoring of a variety of neuropathological conditions using noninvasive brain imaging techniques.