P2Y12 antagonism results in altered interactions between platelets and regulatory T cells during sepsis.

Sepsis is a complex clinical condition resulting from a serious bloodstream infection. With mortality rates as high as 50%, improved treatments are needed. Regulatory T cells (Tregs), a subset of T lymphocytes, promote the resolution of inflammation. Septic patients have elevated levels of circulating Tregs. Platelets influence the proliferation and activation of Tregs in vitro. However, modulating platelet-Tregs interaction during sepsis may restraing Treg proliferation, leading to the restoration of immunologic homeostasis. P2Y12 is a purinergic receptor present on platelets and T lymphocytes. Blocking P2Y12 improves the outcome of sepsis. We investigated whether blocking P2Y12 alters platelet-Treg interaction in vivo. We used the murine model of sepsis, cecal ligation, and puncture (CLP) and we blocked P2Y12 using the P2Y12 antagonist, clopidogrel. Twenty-four hours after surgery, we measured Treg population sizes in the spleens of the Sham, CLP, and CLP + clopidogrel groups. We investigated the effect of blocking P2Y12 in vitro using cocultures of human platelets and T cells with or without anti-CD3/CD28. P2Y12 was blocked using AR-C69931MX. Treg population sizes were reduced in the septic mice treated with clopidogrel compared with untreated septic mice. Aggregation of platelets and CD4+ T cells was reduced in treated CLP mice compared with untreated CLP mice. P2Y12 antagonism changes how platelets influence T cells in vitro, depending on T-cell activation. In conclusion, blockade of the P2Y12 signaling pathway restrains Treg proliferation in vivo and in vitro. Targeting platelets to control Treg proliferation and activity may be a promising strategy for treating sepsis.

ADP exerts P2Y12 -dependent and P2Y12 -independent effects on primary human T cell responses to stimulation.

Purinergic signaling plays a complex role in inflammation. Nucleotides released by T lymphocytes, endothelial cells, and platelets during inflammation induce cellular responses by binding to receptors that regulate intracellular signaling pathways. Previous studies have found that purinergic signaling can have both proinflammatory and anti-inflammatory effects, but the roles of specific pathways in specific cell types are poorly understood. We investigated the role of the P2Y12 signaling pathway in the activation of T lymphocytes in vitro. We isolated peripheral blood mononuclear cells (PBMCs) from healthy donors and pretreated them with ADP (a P2Y12 agonist), AR-C69931MX (a P2Y12 antagonist), or both. We then stimulated PBMC using phytohemagglutinin (PHA) or anti-CD3/CD28 antibodies. We found that ADP affects T cell responses in term of cell activity and receptor expression through both P2Y12-dependent and P2Y12-independent pathways and other responses (cytokine secretion) primarily through P2Y12 -independent pathways. The ADP-mediated effect changed over time and was stimulus-specific.