Microglia priming - a role in ME?

Professor Hugh Perry from University of Southampton gave an absolut wonderful presentation on the INVEST in ME conference in June 2012. I have just seen his prensentation on the conference DVD - twice!!

(I can highly recommend the DVDs from the conference. You need to have a little medical insight to understand them. You can buy them here.)

Professor Hugh Perry is not a ME researcher, but is a professor of experimental neuropathology. He researches in Inflammation in the CNS and its contribution to Neurological Disease.

From his article Contribution of systemic inflammation to chronic neurodegeneration:

"Systemic infection or inflammation gives rise to signals that communicate with the brain and leads to changes in metabolism and behaviour collectively known as sickness behaviour. In healthy young individuals, these changes are normally transient with no long-term consequences. The microglia are involved in the immune to brain signalling pathways. In the aged or diseased brain, the microglia have a primed phenotype as a consequence of changes in their local microenvironment. Systemic inflammation impacts on these primed microglia and switches them from a relatively benign to an aggressive phenotype with the enhanced synthesis of pro-inflammatory mediators. Recent evidence suggests that systemic inflammation contributes to the exacerbation of acute symptoms of chronic neurodegenerative disease and may accelerate disease progression. The normal homeostatic role that microglia play in signalling about systemic infections and inflammation becomes maladaptive in the aged and diseased brain and this offers a route to therapeutic intervention. Prompt treatment of systemic inflammation or blockade of signalling pathways from the periphery to the brain may help to slow neurodegeneration and improve the quality of life for individuals suffering from chronic neurodegenerative disease."

If ME is a neurodegererative disease with microglia priming, it could explain why ME patients are getting worse after an infection.

I looked for more articles about microglia priming:

The conclusion from this study Long-term impact of systemic bacterial infection on the cerebral vasculature and microglia:
"These studies reveal that the innate immune cells in the brain do not become tolerant to systemic infection, but are primed instead. This may lead to prolonged and damaging cytokine production that may have a profound effect on the onset and/or progression of pre-existing neurodegenerative disease."

The abstract from this study Glucocorticoids mediate stress-induced priming of microglial pro-inflammatory responses:
"Acute and chronic stress sensitizes or "primes" the neuroinflammatory response to a subsequent pro-inflammatory challenge. While prior evidence shows that glucocorticoids (GCs) play a pivotal role in stress-induced potentiation of neuroinflammatory responses, it remains unclear whether stress-induced GCs sensitize the response of key CNS immune substrates (i.e. microglia) to pro-inflammatory stimuli. An ex vivo approach was used to address this question. Here, stress-induced GC signaling was manipulated in vivo and hippocampal microglia challenged with the pro-inflammatory stimulus LPS ex vivo. Male Sprague-Dawley rats were either pretreated in vivo with the GC receptor antagonist RU486 or adrenalectomized (ADX). Animals were then exposed to an acute stressor (inescapable tailshock; IS) and 24 h later hippocampal microglia were isolated and challenged with LPS to probe for stress-induced sensitization of pro-inflammatory responses. Prior exposure to IS resulted in a potentiated pro-inflammatory cytokine response (e.g. IL-1β gene expression) to LPS in isolated microglia. Treatment in vivo with RU486 and ADX inhibited or completely blocked this IS-induced sensitization of the microglial pro-inflammatory response. The present results suggest that stress-induced GCs function to sensitize the microglial pro-inflammatory response (IL-1β, IL-6, NFκBIα) to immunologic challenges."

This is also interesting Minocycline attenuates microglia activation and blocks the long-term epileptogenic effects of early-life seizures:
"Inhibition of seizure-induced inflammation by 7 day minocycline post-treatment abrogated both the exaggerated microglia activation and the increased susceptibility to the second seizure later in life. The priming effect of early-life seizures is accompanied by modified and rapidly reactivated microglia. Our results suggest that anti-inflammatory therapy after SE may be useful to block the epileptogenic process and mitigate the long-term damaging effects of early-life seizures."

And this Beta-adrenergic receptor activation primes microglia cytokine production:
"Exaggerated pro-inflammatory cytokine production by primed microglia is thought to mediate pathology during stress, aging, and neurodegeneration. Recently, it was demonstrated that beta-adrenergic receptor (β-AR) antagonism prevents priming of microglia in mice exposed to chronic stress. To determine if β-AR stimulation is sufficient to prime microglia, rats were intra-cerebroventricularly administered isoproterenol (β-AR agonist) or vehicle and 24h later hippocampal microglia were placed in culture with media or LPS. Prior isoproterenol treatment significantly enhanced IL-1β and IL-6, but not TNF-α production following LPS stimulation. These data suggest that central β-AR stimulation is sufficient to prime microglia cytokine responses."