Platelet-Depletion of Whole Blood Reveals That Platelets Potentiate the Release of IL-8 From Leukocytes Into Plasma in a Thrombin-Dependent Manner

• Published in: Frontiers in immunology Vol. 13; p. 865386
• Main Authors: Quach, Huy Quang, Johnson, Christina, Ekholt, Karin, Islam, Rakibul, Mollnes, Tom Eirik, Nilsson, Per H
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media 04.04.2022; Frontiers Media S.A
• Subjects: acute inflammation; Biochemistry; Biokemi; Blood Platelets - metabolism; cytokines; Cytokines - metabolism; human whole blood; Humans; IL-8; Immunology; Interleukin-8 - metabolism; Leukocytes - metabolism; platelets; thrombin; Thrombin - metabolism; Thrombin - pharmacology; acute inflammation; human whole blood; cytokines; thrombin; IL-8; platelets
• ISSN: 1664-3224; 1664-3224
• DOI: 10.3389/fimmu.2022.865386

In a recent study, we found an elevated level of interleukin 8 (IL-8) in response to bacterial incubation in thrombin-sufficient human whole blood anticoagulated by the fibrin polymerization blocking peptide GPRP. Whether thrombin directly activated leukocytes or mediated the release thrombin-dependent activation of platelets remains unresolved. Herein, we addressed the role of thrombin and platelets in IL-8 release. We separated platelets from whole blood using a combination of 0.7% (w/v) citrate and GPRP for attenuating the hemostatic response during the separation of platelets. Cytokine responses were compared in whole blood and platelet-depleted blood upon incubation. Cytokine responses were also profiled with and without reconstitution of either platelets or the supernatant from activated platelets. Platelets were not activated during the separation process but responded to stimuli upon re-calcification. Plasma levels of IL-1β, IL-1Ra, IL-6, IL-8, IP-10, MIP-1α, and MIP-1β were significantly reduced in platelet-depleted blood compared to whole blood, but recovered in the presence of platelets, or with the supernatant of activated platelets. The leukocyte fraction and platelets were each found to contribute to the elevation of IL-8 at around 5 ng/ml; however, if combined, the release of IL-8 increased to 26 ng/ml. This process was dependent on thrombin since the levels of IL-8 remained at 5 ng/ml in whole blood if thrombin was blocked. Intracellular staining revealed that monocytes were the main source for IL-8 expression. Our findings suggest that the release of IL-8 is mediated by the leukocytes, mainly monocytes, but potentiated thrombin-dependent activation of platelets.