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Absence of the P2X7 receptor alters leukocyte function and attenuates an inflammatory response
Jeffrey M Labasi1, Nina Petrushova, Carol Donovan
1Department of Antibacterials, Immunology, and Inflammation, Pfizer Global Research and Development, Pfizer Inc., Groton, CT 06340, USA.
Abstract:
When challenged with extracellular ATP, leukocytes respond and activate processes attributed to the P2X(7) receptor (P2X(7)R), an unusual ligand-gated ion channel. To prove P2X(7)R involvement, blood samples from P2X(7)R-deficient mice were characterized. Monocytes and lymphocytes associated with wild-type blood responded to ATP and underwent volume/shape changes and shed L-selectin. In contrast, leukocytes from P2X(7)R-deficient animals demonstrated no change in physical properties or L-selectin expression following ATP challenge. Blood stimulated with LPS or ATP individually generated minimal quantities of the leaderless polypeptide IL-1 beta, but sequential treatment of wild-type, but not P2X(7)R-deficient, blood with LPS and ATP yielded large amounts of cell-free cytokine. Based on these differences, wild-type and P2X(7)R-deficient animals were compared following induction of monoclonal anti-collagen-induced arthritis. Ab-treated wild-type animals subsequently challenged with LPS developed inflamed, swollen paws; their joint cartilage demonstrated lesions, loss of proteoglycan content, and the presence of collagen degradation products. P2X(7)R-deficient animals subjected to the same challenge were markedly less affected; both the incidence and severity of disease were reduced. These data indicate that ATP does act via the P2X(7)R to affect leukocyte function and that the P2X(7)R can serve as an important component of an in vivo inflammatory response.
Insights
Extracellular ATP activates leukocytes via the P2X(7) receptor (P2X(7)R), a key player in inflammation. P2X(7)R deficiency significantly reduces leukocyte activation and inflammatory responses in arthritis models.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Leukocytes respond to extracellular ATP through the P2X(7) receptor (P2X(7)R).
- P2X(7)R is an ion channel involved in cellular activation and inflammatory mediator release.
- The role of P2X(7)R in vivo inflammatory conditions requires further elucidation.
Purpose of the Study:
- To investigate the functional role of the P2X(7) receptor in leukocyte activation.
- To determine the involvement of P2X(7)R in the inflammatory response during an in vivo arthritis model.
Main Methods:
- Characterization of leukocytes from P2X(7)R-deficient and wild-type mice.
- Assessment of leukocyte responses (volume changes, L-selectin shedding) to ATP stimulation.
- Analysis of IL-1 beta release following LPS and ATP co-stimulation.
- Induction of anti-collagen antibody-induced arthritis in P2X(7)R-deficient and wild-type mice, followed by LPS challenge.
Main Results:
- Wild-type leukocytes responded to ATP with volume changes and L-selectin shedding, unlike P2X(7)R-deficient leukocytes.
- Sequential LPS and ATP stimulation induced significant IL-1 beta release in wild-type blood but not in P2X(7)R-deficient blood.
- P2X(7)R-deficient mice exhibited significantly reduced incidence and severity of arthritis, including less joint inflammation and cartilage damage, compared to wild-type mice.
Conclusions:
- Extracellular ATP acts via the P2X(7) receptor to modulate leukocyte function.
- The P2X(7) receptor is a critical mediator of inflammatory responses in vivo.
- Targeting the P2X(7) receptor may offer a therapeutic strategy for inflammatory diseases like arthritis.