ATP, a danger signal, activates human eosinophils via P2 purinergic receptors

Background:Eosinophils recognize various stimuli resulting in their accumulation in mucosal tissues and the progression of inflammation. Uric acid (UA) is an important endogenous danger signal released from injured cells by inflammation and infection. Eosinophils are also involved in innate Th2-type immune responses mediated through endogenous danger signals, including IL-33, uric acid (UA), or ATP, in non-sensitized mice exposed to environmental allergens. However, the mechanism involved in eosinophil responses to these danger signals remains insufficiently understood.

Methods: Eosinophils isolated from peripheral blood of normal individuals were incubated in the presence or absence of monosodium urate (MSU) crystals and ATPγS, a non-hydrolysable ATP analogue. To determine the involvement of P2 or P2Y₂ receptors in eosinophil responses to UA and ATP, eosinophils were preincubated with a pan-P2 receptor inhibitor, oxidized ATP (oATP), or anti-P2Y₂antibody before incubation with MSU crystals or ATPγS.

Results: MSU crystals induced adhesion of eosinophils to recombinant human (rh)-ICAM-1 and induced production of superoxide anion. oATP abolished eosinophil responses to MSU crystals, suggesting involvement of endogenous ATP and its receptors. Furthermore, exogenous ATP, as ATPγS, activated eosinophils and induced migration across a model of basement membrane, adhesion to rh-ICAM-1, generation of superoxide anion, and degranulation of eosinophil-derived neurotoxin (EDN). oATP and anti-P2Y₂significantly reduced these eosinophil responses.

Conclusions: UA stimulated eosinophils to release ATP. ATP serves as an essential mediator of functional responses in human eosinophils. Thus, human eosinophils may respond to particulate damage-associated endogenous danger signals. These responses by eosinophils to tissue damage may explain the self-perpetuating nature of airway inflammation in patients with asthma.