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2016 ; 7
(ä): 74
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Purinergic Signaling to Terminate TLR Responses in Macrophages
#MMPMID26973651
Hamidzadeh K
; Mosser DM
Front Immunol
2016[]; 7
(ä): 74
PMID26973651
show ga
Macrophages undergo profound physiological alterations when they encounter
pathogen-associated molecular patterns (PAMPs). These alterations can result in
the elaboration of cytokines and mediators that promote immune responses and
contribute to the clearance of pathogens. These innate immune responses by
myeloid cells are transient. The termination of these secretory responses is not
due to the dilution of stimuli, but rather to the active downregulation of innate
responses induced by the very PAMPs that initiated them. Here, we describe a
purinergic autoregulatory program whereby TLR-stimulated macrophages control
their activation state. In this program, TLR-stimulated macrophages undergo
metabolic alterations that result in the production of ATP and its release
through membrane pannexin channels. This purine nucleotide is rapidly hydrolyzed
to adenosine by ectoenzymes on the macrophage surface, CD39 and CD73. Adenosine
then signals through the P1 class of seven transmembrane receptors to induce a
regulatory state that is characterized by the downregulation of inflammatory
cytokines and the production of anti-inflammatory cytokines and growth factors.
This purinergic autoregulatory system mitigates the collateral damage that would
be caused by the prolonged activation of macrophages and rather allows the
macrophage to maintain homeostasis. The transient activation of macrophages can
be prolonged by treating macrophages with IFN-?. IFN-?-treated macrophages become
less sensitive to the regulatory effects of adenosine, allowing them to sustain
macrophage activation for the duration of an adaptive immune response.