page_title: Purinergic signalling
section_title: Immune system
hierarchical_section_title: Purinergic signalling / Purinergic signalling in humans / Immune system
caption_attribution_description: English: Intracellular pathways in immune cells stimulated by P2X7 receptor activation
context_page_description: Purinergic signalling is a form of extracellular signalling mediated by purine nucleotides and nucleosides such as adenosine and ATP. It involves the activation of purinergic receptors in the cell and/or in nearby cells, thereby regulating cellular functions.
  The purinergic signalling complex of a cell is sometimes referred to as the “purinome”.
context_section_description: Autocrine purinergic signalling is an important checkpoint in the activation of white blood cells. These mechanisms either enhance or inhibit cell activation based on the purinergic receptors involved, allowing cells to adjust their functional responses initiated by extracellular environmental cues.
  Like most immunomodulating agents, ATP can act either as an immunosuppressive or an immunostimulatory factor, depending on the cytokine microenviroment and the type of cell receptor. In white blood cells such as macrophages, dendritic cells, lymphocytes, eosinophils, and mast cells, purinergic signalling plays a pathophysiological role in calcium mobilization, actin polymerization, release of mediators, cell maturation, cytotoxicity, and apoptosis. Large increases in extracellular ATP that are associated with cell death serve as a "danger signal" in the inflammatory processes.
  In neutrophils, tissue adenosine can either activate or inhibit various neutrophil functions, depending on the inflammatory microenvironment, the expression of adenosine receptors on the neutrophil, and the affinity of these receptors for adenosine. Micromolar concentrations of adenosine activate A2A and A2B receptors. This inhibits the release of granules and prevents oxidative burst. On the other hand, nanomolar concentrations of adenosine activate A1 and A3 receptors, resulting in neutrophilic chemotaxis towards inflammatory stimuli. The release of ATP and an autocrine feedback through P2RY2 and A3 receptors are signal amplifiers. Hypoxia-inducible factors also influence adenosine signalling.
caption: As part of the inflammatory response, ATP activates the P2RX7 receptor, triggering a drop in intracellular potassium levels and the formation of inflammasomes
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