Immune response in the human brain accurately measured for the first time ever.

Scientists have long suspected that neuroinflammation caused by a reactive immune system could be tripping off the neurodegeneration seen in certain dementias, multiple sclerosis, and other deadly diseases of the nervous system. Now, a novel molecular imaging technique could be the key to understanding how best to treat these and other devastating diseases, according to a new study from Yale University.

The researchers state at the heart of this maladaptive immune response are microglia, immune cells in the central nervous system that can be activated to trigger neuroinflammation. For the current study, researchers used positron emission tomography (PET) to measure activation of microglia by employing a molecule from E. coli bacteria called lipopolysaccharide (LPS), or endotoxin. LPS stimulates the immune system and is accompanied by a radiotracer called carbon-11 PBR28 (C-11 PBR28). The team explains this form of molecular imaging allows the minimally invasive visualization of neuroinflammation. C-11 PBR28, is injected and binds to translocator proteins expressed on activated microglia. A PET scanner can then detect the radioactive particles emitted from inside the brain, representing areas of increased microglial activation before and after immune stimulation with LPS.  The team presented their findings at the 2015 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging (SNMMI).

The imaging technique could shed light on the immune dysfunction underpinning a broad range of neuroinflammatory diseases, such as Alzheimer’s disease, depression, post-traumatic stress disorder and addiction, states the team.  They go on to add this is the first human study to accurately measures this immune response in the brain and the discoveries made with this technique could contribute to promising new drug treatments.

In the current study PET radiotracer C-11 PBR28 was administered to eight healthy men aged between nineteen and thirty-one years of age, followed by two separate PET scans on the same day for each subject before and after injection with LPS. Adverse symptoms were self-reported and blood samples were taken to assess levels of peripheral inflammation.  The data findings show administering LPS led to a substantial spike in the systemic inflammatory response and levels of reported sickness, and activated microglia in the central nervous system.

The team surmises with further research, eventual drug therapies could potentially cut the activation of neurodegenerative microglia and encourage neuroprotective processes in the brain.

Source:  Yale School of Medicine

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